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142-424: Chlorine is a chemical element ; it has symbol Cl and atomic number 17. The second-lightest of the halogens , it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is a yellow-green gas at room temperature. It is an extremely reactive element and a strong oxidising agent : among the elements, it has the highest electron affinity and

284-738: A pure element . In chemistry, a pure element means a substance whose atoms all (or in practice almost all) have the same atomic number, or number of protons . Nuclear scientists, however, define a pure element as one that consists of only one isotope. For example, a copper wire is 99.99% chemically pure if 99.99% of its atoms are copper, with 29 protons each. However it is not isotopically pure since ordinary copper consists of two stable isotopes, 69% Cu and 31% Cu, with different numbers of neutrons. However, pure gold would be both chemically and isotopically pure, since ordinary gold consists only of one isotope, Au. Atoms of chemically pure elements may bond to each other chemically in more than one way, allowing

426-426: A 1:1 mixture of HCl and H 2 O, the system separates completely into two separate liquid phases. Hydrochloric acid forms an azeotrope with boiling point 108.58 °C at 20.22 g HCl per 100 g solution; thus hydrochloric acid cannot be concentrated beyond this point by distillation. Unlike hydrogen fluoride, anhydrous liquid hydrogen chloride is difficult to work with as a solvent, because its boiling point

568-429: A chlorine derivative of perchloric acid (HOClO 3 ), similar to the thermally unstable chlorine derivatives of other oxoacids: examples include chlorine nitrate (ClONO 2 , vigorously reactive and explosive), and chlorine fluorosulfate (ClOSO 2 F, more stable but still moisture-sensitive and highly reactive). Dichlorine hexoxide is a dark-red liquid that freezes to form a solid which turns yellow at −180 °C: it

710-414: A chlorofluorinating agent, adding chlorine and fluorine across a multiple bond or by oxidation: for example, it will attack carbon monoxide to form carbonyl chlorofluoride, COFCl. It will react analogously with hexafluoroacetone , (CF 3 ) 2 CO, with a potassium fluoride catalyst to produce heptafluoroisopropyl hypochlorite, (CF 3 ) 2 CFOCl; with nitriles RCN to produce RCF 2 NCl 2 ; and with

852-549: A considerable amount of time. (See element naming controversy ). Precursors of such controversies involved the nationalistic namings of elements in the late 19th century. For example, lutetium was named in reference to Paris, France. The Germans were reluctant to relinquish naming rights to the French, often calling it cassiopeium . Similarly, the British discoverer of niobium originally named it columbium , in reference to

994-744: A dangerously powerful and unstable oxidizer. Near the end of the nineteenth century, E. S. Smith patented a method of sodium hypochlorite production involving electrolysis of brine to produce sodium hydroxide and chlorine gas, which then mixed to form sodium hypochlorite. This is known as the chloralkali process , first introduced on an industrial scale in 1892, and now the source of most elemental chlorine and sodium hydroxide. In 1884 Chemischen Fabrik Griesheim of Germany developed another chloralkali process which entered commercial production in 1888. Elemental chlorine solutions dissolved in chemically basic water (sodium and calcium hypochlorite ) were first used as anti- putrefaction agents and disinfectants in

1136-477: A different element in nuclear reactions , which change an atom's atomic number. Historically, the term "chemical element" meant a substance that cannot be broken down into constituent substances by chemical reactions, and for most practical purposes this definition still has validity. There was some controversy in the 1920s over whether isotopes deserved to be recognized as separate elements if they could be separated by chemical means. The term "(chemical) element"

1278-652: A few decay products, to have been differentiated from other elements. Most recently, the synthesis of element 118 (since named oganesson ) was reported in October 2006, and the synthesis of element 117 ( tennessine ) was reported in April 2010. Of these 118 elements, 94 occur naturally on Earth. Six of these occur in extreme trace quantities: technetium , atomic number 43; promethium , number 61; astatine , number 85; francium , number 87; neptunium , number 93; and plutonium , number 94. These 94 elements have been detected in

1420-529: A few elements, such as silver and gold , are found uncombined as relatively pure native element minerals . Nearly all other naturally occurring elements occur in the Earth as compounds or mixtures. Air is mostly a mixture of molecular nitrogen and oxygen , though it does contain compounds including carbon dioxide and water , as well as atomic argon , a noble gas which is chemically inert and therefore does not undergo chemical reactions. The history of

1562-444: A fluoride ion donor or acceptor (Lewis base or acid), although it does not dissociate appreciably into ClF 2 and ClF 4 ions. Chlorine pentafluoride (ClF 5 ) is made on a large scale by direct fluorination of chlorine with excess fluorine gas at 350 °C and 250 atm, and on a small scale by reacting metal chlorides with fluorine gas at 100–300 °C. It melts at −103 °C and boils at −13.1 °C. It

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1704-776: A low-pressure discharge tube. The yellow [Cl 3 ] cation is more stable and may be produced as follows: This reaction is conducted in the oxidising solvent arsenic pentafluoride . The trichloride anion, [Cl 3 ] , has also been characterised; it is analogous to triiodide . The three fluorides of chlorine form a subset of the interhalogen compounds, all of which are diamagnetic . Some cationic and anionic derivatives are known, such as ClF 2 , ClF 4 , ClF 2 , and Cl 2 F. Some pseudohalides of chlorine are also known, such as cyanogen chloride (ClCN, linear), chlorine cyanate (ClNCO), chlorine thiocyanate (ClSCN, unlike its oxygen counterpart), and chlorine azide (ClN 3 ). Chlorine monofluoride (ClF)

1846-431: A lower freezing point than pure water, putting salt or saltwater on ice that is below 0 °C (32 °F) will cause it to melt—this effect is called freezing-point depression . It is common for homeowners in cold climates to spread salt on their sidewalks and driveways after a snow storm to melt the ice. It is not necessary to use so much salt that the ice is completely melted; rather, a small amount of salt will weaken

1988-500: A pressure of 1 bar and a given temperature (typically at 298.15K). However, for phosphorus, the reference state is white phosphorus even though it is not the most stable allotrope, and the reference state for carbon is graphite, because the structure of graphite is more stable than that of the other allotropes. In thermochemistry , an element is defined to have an enthalpy of formation of zero in its reference state. Several kinds of descriptive categorizations can be applied broadly to

2130-483: A pressure of one atmosphere, are commonly used in characterizing the various elements. While known for most elements, either or both of these measurements is still undetermined for some of the radioactive elements available in only tiny quantities. Since helium remains a liquid even at absolute zero at atmospheric pressure, it has only a boiling point, and not a melting point, in conventional presentations. The density at selected standard temperature and pressure (STP)

2272-518: A reduction in oxidation state , which can also be achieved by reducing a higher chloride using hydrogen or a metal as a reducing agent. This may also be achieved by thermal decomposition or disproportionation as follows: Most metal chlorides with the metal in low oxidation states (+1 to +3) are ionic. Nonmetals tend to form covalent molecular chlorides, as do metals in high oxidation states from +3 and above. Both ionic and covalent chlorides are known for metals in oxidation state +3 (e.g. scandium chloride

2414-407: A result of the increasing molecular weight of the halogens down the group, the density and heats of fusion and vaporisation of chlorine are again intermediate between those of bromine and fluorine, although all their heats of vaporisation are fairly low (leading to high volatility) thanks to their diatomic molecular structure. The halogens darken in colour as the group is descended: thus, while fluorine

2556-483: A separate gaseous substance was recognised by the Brabantian chemist and physician Jan Baptist van Helmont . The element was first studied in detail in 1774 by Swedish chemist Carl Wilhelm Scheele , and he is credited with the discovery. Scheele produced chlorine by reacting MnO 2 (as the mineral pyrolusite ) with HCl: Scheele observed several of the properties of chlorine: the bleaching effect on litmus ,

2698-456: A small group, (the metalloids ), having intermediate properties and often behaving as semiconductors . A more refined classification is often shown in colored presentations of the periodic table. This system restricts the terms "metal" and "nonmetal" to only certain of the more broadly defined metals and nonmetals, adding additional terms for certain sets of the more broadly viewed metals and nonmetals. The version of this classification used in

2840-624: A solution of sodium carbonate. The resulting liquid, known as " Eau de Javel " (" Javel water "), was a weak solution of sodium hypochlorite . This process was not very efficient, and alternative production methods were sought. Scottish chemist and industrialist Charles Tennant first produced a solution of calcium hypochlorite ("chlorinated lime"), then solid calcium hypochlorite (bleaching powder). These compounds produced low levels of elemental chlorine and could be more efficiently transported than sodium hypochlorite, which remained as dilute solutions because when purified to eliminate water, it became

2982-474: A whole number. For example, the relative atomic mass of chlorine is 35.453 u, which differs greatly from a whole number as it is an average of about 76% chlorine-35 and 24% chlorine-37. Whenever a relative atomic mass value differs by more than ~1% from a whole number, it is due to this averaging effect, as significant amounts of more than one isotope are naturally present in a sample of that element. Chemists and nuclear scientists have different definitions of

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3124-456: A wide variety of different rock salts for different dishes. Pure salt is avoided as particular colors of salt indicates the presence of different impurities. Many recipes call for particular kinds of rock salt, and imported pure salt often has impurities added to adapt to local tastes. Historically , salt was used as a form of currency in barter systems and was exclusively controlled by authorities and their appointees. In some ancient civilizations

3266-415: Is hydrogen chloride , HCl, a major chemical in industry as well as in the laboratory, both as a gas and dissolved in water as hydrochloric acid . It is often produced by burning hydrogen gas in chlorine gas, or as a byproduct of chlorinating hydrocarbons . Another approach is to treat sodium chloride with concentrated sulfuric acid to produce hydrochloric acid, also known as the "salt-cake" process: In

3408-440: Is sodium chlorate , mostly used to make chlorine dioxide to bleach paper pulp. The decomposition of chlorate to chloride and oxygen is a common way to produce oxygen in the laboratory on a small scale. Chloride and chlorate may comproportionate to form chlorine as follows: Perchlorates and perchloric acid (HOClO 3 ) are the most stable oxo-compounds of chlorine, in keeping with the fact that chlorine compounds are most stable when

3550-404: Is 10 (for tin , element 50). The mass number of an element, A , is the number of nucleons (protons and neutrons) in the atomic nucleus. Different isotopes of a given element are distinguished by their mass number, which is written as a superscript on the left hand side of the chemical symbol (e.g., U). The mass number is always an integer and has units of "nucleons". Thus, magnesium-24 (24

3692-883: Is a chemical substance whose atoms all have the same number of protons . The number of protons is called the atomic number of that element. For example, oxygen has an atomic number of 8, meaning each oxygen atom has 8 protons in its nucleus. Atoms of the same element can have different numbers of neutrons in their nuclei, known as isotopes of the element. Two or more atoms can combine to form molecules . Some elements are formed from molecules of identical atoms , e. g. atoms of hydrogen (H) form diatomic molecules (H 2 ). Chemical compounds are substances made of atoms of different elements; they can have molecular or non-molecular structure. Mixtures are materials containing different chemical substances; that means (in case of molecular substances) that they contain different types of molecules. Atoms of one element can be transformed into atoms of

3834-606: Is a mixture of C (about 98.9%), C (about 1.1%) and about 1 atom per trillion of C. Most (54 of 94) naturally occurring elements have more than one stable isotope. Except for the isotopes of hydrogen (which differ greatly from each other in relative mass—enough to cause chemical effects), the isotopes of a given element are chemically nearly indistinguishable. All elements have radioactive isotopes (radioisotopes); most of these radioisotopes do not occur naturally. Radioisotopes typically decay into other elements via alpha decay , beta decay , or inverse beta decay ; some isotopes of

3976-406: Is a dimensionless number equal to the atomic mass divided by the atomic mass constant , which equals 1 Da. In general, the mass number of a given nuclide differs in value slightly from its relative atomic mass, since the mass of each proton and neutron is not exactly 1 Da; since the electrons contribute a lesser share to the atomic mass as neutron number exceeds proton number; and because of

4118-472: Is a pale yellow gas, chlorine is distinctly yellow-green. This trend occurs because the wavelengths of visible light absorbed by the halogens increase down the group. Specifically, the colour of a halogen, such as chlorine, results from the electron transition between the highest occupied antibonding π g molecular orbital and the lowest vacant antibonding σ u molecular orbital. The colour fades at low temperatures, so that solid chlorine at −195 °C

4260-472: Is a poor solvent, only able to dissolve small molecular compounds such as nitrosyl chloride and phenol , or salts with very low lattice energies such as tetraalkylammonium halides. It readily protonates electrophiles containing lone-pairs or π bonds. Solvolysis , ligand replacement reactions, and oxidations are well-characterised in hydrogen chloride solution: Nearly all elements in the periodic table form binary chlorides. The exceptions are decidedly in

4402-480: Is a very poor conductor of electricity, and indeed its conductivity is so low as to be practically unmeasurable. Chlorine has two stable isotopes, Cl and Cl. These are its only two natural isotopes occurring in quantity, with Cl making up 76% of natural chlorine and Cl making up the remaining 24%. Both are synthesised in stars in the oxygen-burning and silicon-burning processes . Both have nuclear spin 3/2+ and thus may be used for nuclear magnetic resonance , although

Chlorine - Misplaced Pages Continue

4544-429: Is a very strong fluorinating agent, although it is still not as effective as chlorine trifluoride. Only a few specific stoichiometric reactions have been characterised. Arsenic pentafluoride and antimony pentafluoride form ionic adducts of the form [ClF 4 ][MF 6 ] (M = As, Sb) and water reacts vigorously as follows: The product, chloryl fluoride , is one of the five known chlorine oxide fluorides. These range from

4686-441: Is a weak ligand, weaker than water, a few compounds involving coordinated ClO 4 are known. The Table below presents typical oxidation states for chlorine element as given in the secondary schools or colleges. There are more complex chemical compounds, the structure of which can only be explained using modern quantum chemical methods, for example, cluster technetium chloride [(CH 3 ) 4 N] 3 [Tc 6 Cl 14 ], in which 6 of

4828-505: Is almost colourless. Like solid bromine and iodine, solid chlorine crystallises in the orthorhombic crystal system , in a layered lattice of Cl 2 molecules. The Cl–Cl distance is 198 pm (close to the gaseous Cl–Cl distance of 199 pm) and the Cl···Cl distance between molecules is 332 pm within a layer and 382 pm between layers (compare the van der Waals radius of chlorine, 180 pm). This structure means that chlorine

4970-470: Is also produced when photolysing the solid at −78 °C: it is a dark brown solid that explodes below 0 °C. The ClO radical leads to the depletion of atmospheric ozone and is thus environmentally important as follows: Chlorine perchlorate (ClOClO 3 ) is a pale yellow liquid that is less stable than ClO 2 and decomposes at room temperature to form chlorine, oxygen, and dichlorine hexoxide (Cl 2 O 6 ). Chlorine perchlorate may also be considered

5112-812: Is an ongoing area of scientific study. The lightest elements are hydrogen and helium , both created by Big Bang nucleosynthesis in the first 20 minutes of the universe in a ratio of around 3:1 by mass (or 12:1 by number of atoms), along with tiny traces of the next two elements, lithium and beryllium . Almost all other elements found in nature were made by various natural methods of nucleosynthesis . On Earth, small amounts of new atoms are naturally produced in nucleogenic reactions, or in cosmogenic processes, such as cosmic ray spallation . New atoms are also naturally produced on Earth as radiogenic daughter isotopes of ongoing radioactive decay processes such as alpha decay , beta decay , spontaneous fission , cluster decay , and other rarer modes of decay. Of

5254-460: Is based on a Latin or other traditional word, for example adopting "gold" rather than "aurum" as the name for the 79th element (Au). IUPAC prefers the British spellings " aluminium " and "caesium" over the U.S. spellings "aluminum" and "cesium", and the U.S. "sulfur" over British "sulphur". However, elements that are practical to sell in bulk in many countries often still have locally used national names, and countries whose national language does not use

5396-658: Is even more unstable and cannot be isolated or concentrated without decomposition: it is known from the decomposition of aqueous chlorine dioxide. However, sodium chlorite is a stable salt and is useful for bleaching and stripping textiles, as an oxidising agent, and as a source of chlorine dioxide. Chloric acid (HOClO 2 ) is a strong acid that is quite stable in cold water up to 30% concentration, but on warming gives chlorine and chlorine dioxide. Evaporation under reduced pressure allows it to be concentrated further to about 40%, but then it decomposes to perchloric acid, chlorine, oxygen, water, and chlorine dioxide. Its most important salt

5538-894: Is extremely dangerous, and poisonous to most living organisms. As a chemical warfare agent, chlorine was first used in World War ;I as a poison gas weapon. In the form of chloride ions , chlorine is necessary to all known species of life. Other types of chlorine compounds are rare in living organisms, and artificially produced chlorinated organics range from inert to toxic. In the upper atmosphere , chlorine-containing organic molecules such as chlorofluorocarbons have been implicated in ozone depletion . Small quantities of elemental chlorine are generated by oxidation of chloride ions in neutrophils as part of an immune system response against bacteria. The most common compound of chlorine, sodium chloride, has been known since ancient times; archaeologists have found evidence that rock salt

5680-551: Is extremely thermally stable, and is sold commercially in 500-gram steel lecture bottles. It is a colourless gas that melts at −155.6 °C and boils at −100.1 °C. It may be produced by the reaction of its elements at 225 °C, though it must then be separated and purified from chlorine trifluoride and its reactants. Its properties are mostly intermediate between those of chlorine and fluorine. It will react with many metals and nonmetals from room temperature and above, fluorinating them and liberating chlorine. It will also act as

5822-514: Is less reactive than fluorine and more reactive than bromine. It is also a weaker oxidising agent than fluorine, but a stronger one than bromine. Conversely, the chloride ion is a weaker reducing agent than bromide, but a stronger one than fluoride. It is intermediate in atomic radius between fluorine and bromine, and this leads to many of its atomic properties similarly continuing the trend from iodine to bromine upward, such as first ionisation energy , electron affinity , enthalpy of dissociation of

Chlorine - Misplaced Pages Continue

5964-441: Is less than +1.395 V, it would be expected that chlorine should be able to oxidise water to oxygen and hydrochloric acid. However, the kinetics of this reaction are unfavorable, and there is also a bubble overpotential effect to consider, so that electrolysis of aqueous chloride solutions evolves chlorine gas and not oxygen gas, a fact that is very useful for the industrial production of chlorine. The simplest chlorine compound

6106-476: Is low, it has a small liquid range, its dielectric constant is low and it does not dissociate appreciably into H 2 Cl and HCl 2 ions – the latter, in any case, are much less stable than the bifluoride ions ( HF 2 ) due to the very weak hydrogen bonding between hydrogen and chlorine, though its salts with very large and weakly polarising cations such as Cs and NR 4 (R = Me , Et , Bu ) may still be isolated. Anhydrous hydrogen chloride

6248-437: Is made by reacting anhydrous sodium perchlorate or barium perchlorate with concentrated hydrochloric acid, filtering away the chloride precipitated and distilling the filtrate to concentrate it. Anhydrous perchloric acid is a colourless mobile liquid that is sensitive to shock that explodes on contact with most organic compounds, sets hydrogen iodide and thionyl chloride on fire and even oxidises silver and gold. Although it

6390-425: Is mostly ionic, but aluminium chloride is not). Silver chloride is very insoluble in water and is thus often used as a qualitative test for chlorine. Although dichlorine is a strong oxidising agent with a high first ionisation energy, it may be oxidised under extreme conditions to form the [Cl 2 ] cation. This is very unstable and has only been characterised by its electronic band spectrum when produced in

6532-606: Is occasionally used in agriculture. An example of this would be inducing salt stress to suppress the growth of annual meadow grass in turf production. Other examples involve exposing weeds to salt water to dehydrate and kill them preventing them from affecting other plants. Salt is also used as a household cleaning product. Its coarse nature allows for its use in various cleaning scenarios including grease/oil removal, stain removal, dries out and hardens sticky spills for an easier clean. Some cultures, especially in Africa and Brazil, prefer

6674-436: Is often used in characterizing the elements. Density is often expressed in grams per cubic centimetre (g/cm ). Since several elements are gases at commonly encountered temperatures, their densities are usually stated for their gaseous forms; when liquefied or solidified, the gaseous elements have densities similar to those of the other elements. When an element has allotropes with different densities, one representative allotrope

6816-414: Is one of the most reactive elements. Chlorine is a weaker oxidising agent than fluorine but a stronger one than bromine or iodine. This can be seen from the standard electrode potentials of the X 2 /X couples (F, +2.866  V; Cl, +1.395 V; Br, +1.087  V; I, +0.615 V; At , approximately +0.3  V). However, this trend is not shown in the bond energies because fluorine

6958-399: Is present in solid crystalline hydrogen chloride at low temperatures, similar to the hydrogen fluoride structure, before disorder begins to prevail as the temperature is raised. Hydrochloric acid is a strong acid (p K a = −7) because the hydrogen bonds to chlorine are too weak to inhibit dissociation. The HCl/H 2 O system has many hydrates HCl· n H 2 O for n = 1, 2, 3, 4, and 6. Beyond

7100-410: Is produced in the atmosphere by spallation of Ar by interactions with cosmic ray protons . In the top meter of the lithosphere , Cl is generated primarily by thermal neutron activation of Cl and spallation of K and Ca . In the subsurface environment, muon capture by Ca becomes more important as a way to generate Cl. Chlorine is intermediate in reactivity between fluorine and bromine, and

7242-458: Is quite slow at temperatures below 70 °C in spite of the very favourable equilibrium constant of 10. The chlorate ions may themselves disproportionate to form chloride and perchlorate (4 ClO 3 ⇌ Cl + 3 ClO 4 ) but this is still very slow even at 100 °C despite the very favourable equilibrium constant of 10. The rates of reaction for the chlorine oxyanions increases as the oxidation state of chlorine decreases. The strengths of

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7384-509: Is singular due to its small size, low polarisability, and inability to show hypervalence . As another difference, chlorine has a significant chemistry in positive oxidation states while fluorine does not. Chlorination often leads to higher oxidation states than bromination or iodination but lower oxidation states than fluorination. Chlorine tends to react with compounds including M–M, M–H, or M–C bonds to form M–Cl bonds. Given that E°( ⁠ 1 / 2 ⁠ O 2 /H 2 O) = +1.229 V, which

7526-553: Is the anhydride of perchloric acid (HClO 4 ) and can readily be obtained from it by dehydrating it with phosphoric acid at −10 °C and then distilling the product at −35 °C and 1 mmHg. It is a shock-sensitive, colourless oily liquid. It is the least reactive of the chlorine oxides, being the only one to not set organic materials on fire at room temperature. It may be dissolved in water to regenerate perchloric acid or in aqueous alkalis to regenerate perchlorates. However, it thermally decomposes explosively by breaking one of

7668-429: Is the anhydride. It is thus an effective bleach and is mostly used to make hypochlorites . It explodes on heating or sparking or in the presence of ammonia gas. Chlorine dioxide (ClO 2 ) was the first chlorine oxide to be discovered in 1811 by Humphry Davy . It is a yellow paramagnetic gas (deep-red as a solid or liquid), as expected from its having an odd number of electrons: it is stable towards dimerisation due to

7810-426: Is the mass number) is an atom with 24 nucleons (12 protons and 12 neutrons). Whereas the mass number simply counts the total number of neutrons and protons and is thus an integer, the atomic mass of a particular isotope (or "nuclide") of the element is the mass of a single atom of that isotope, and is typically expressed in daltons (symbol: Da), or universal atomic mass units (symbol: u). Its relative atomic mass

7952-532: Is typically selected in summary presentations, while densities for each allotrope can be stated where more detail is provided. For example, the three familiar allotropes of carbon ( amorphous carbon , graphite , and diamond ) have densities of 1.8–2.1, 2.267, and 3.515 g/cm , respectively. The elements studied to date as solid samples have eight kinds of crystal structures : cubic , body-centered cubic , face-centered cubic, hexagonal , monoclinic , orthorhombic , rhombohedral , and tetragonal . For some of

8094-425: Is used extensively in cooking as a flavor enhancer, and to cure a wide variety of foods such as bacon and fish . It is frequently used in food preservation methods across various cultures. Larger pieces can be ground in a salt mill or dusted over food from a shaker as finishing salt. Halite is also often used both residentially and municipally for managing ice. Because brine (a solution of water and salt) has

8236-417: Is used in two different but closely related meanings: it can mean a chemical substance consisting of a single kind of atoms, or it can mean that kind of atoms as a component of various chemical substances. For example, molecules of water (H 2 O) contain atoms of hydrogen (H) and oxygen (O), so water can be said as a compound consisting of the elements hydrogen (H) and oxygen (O) even though it does not contain

8378-469: Is usually made by reaction of chlorine dioxide with oxygen. Despite attempts to rationalise it as the dimer of ClO 3 , it reacts more as though it were chloryl perchlorate, [ClO 2 ][ClO 4 ], which has been confirmed to be the correct structure of the solid. It hydrolyses in water to give a mixture of chloric and perchloric acids: the analogous reaction with anhydrous hydrogen fluoride does not proceed to completion. Dichlorine heptoxide (Cl 2 O 7 )

8520-429: Is very strong; fullerenes , which have nearly spherical shapes; and carbon nanotubes , which are tubes with a hexagonal structure (even these may differ from each other in electrical properties). The ability of an element to exist in one of many structural forms is known as 'allotropy'. The reference state of an element is defined by convention, usually as the thermodynamically most stable allotrope and physical state at

8662-590: Is widely used. For example, the French chemical terminology distinguishes élément chimique (kind of atoms) and corps simple (chemical substance consisting of a single kind of atoms); the Russian chemical terminology distinguishes химический элемент and простое вещество . Almost all baryonic matter in the universe is composed of elements (among rare exceptions are neutron stars ). When different elements undergo chemical reactions, atoms are rearranged into new compounds held together by chemical bonds . Only

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8804-489: The International Union of Pure and Applied Chemistry (IUPAC) had recognized a total of 118 elements. The first 94 occur naturally on Earth , and the remaining 24 are synthetic elements produced in nuclear reactions. Save for unstable radioactive elements (radioelements) which decay quickly, nearly all elements are available industrially in varying amounts. The discovery and synthesis of further new elements

8946-638: The Latin alphabet are likely to use the IUPAC element names. According to IUPAC, element names are not proper nouns; therefore, the full name of an element is not capitalized in English, even if derived from a proper noun , as in californium and einsteinium . Isotope names are also uncapitalized if written out, e.g., carbon-12 or uranium-235 . Chemical element symbols (such as Cf for californium and Es for einsteinium), are always capitalized (see below). In

9088-656: The New World . It was used extensively as such by American publications before the international standardization (in 1950). Before chemistry became a science , alchemists designed arcane symbols for both metals and common compounds. These were however used as abbreviations in diagrams or procedures; there was no concept of atoms combining to form molecules . With his advances in the atomic theory of matter, John Dalton devised his own simpler symbols, based on circles, to depict molecules. Rock salt Halite dominantly occurs within sedimentary rocks where it has formed from

9230-790: The United States , Philippines , and Canada extensive underground beds extend from the Appalachian Basin of western New York through parts of Ontario and under much of the Michigan Basin . Other deposits are in Ohio , Kansas , New Mexico , Nova Scotia and Saskatchewan . The Khewra salt mine is a massive deposit of halite near Islamabad , Pakistan Dasol , Pangasinan . Salt domes are vertical diapirs or pipe-like masses of salt that have been essentially "squeezed up" from underlying salt beds by mobilization due to

9372-423: The kinetic isotope effect is significant). Thus, all carbon isotopes have nearly identical chemical properties because they all have six electrons, even though they may have 6 to 8 neutrons. That is why atomic number, rather than mass number or atomic weight , is considered the identifying characteristic of an element. The symbol for atomic number is Z . Isotopes are atoms of the same element (that is, with

9514-463: The neutron activation of natural chlorine. The most stable chlorine radioisotope is Cl. The primary decay mode of isotopes lighter than Cl is electron capture to isotopes of sulfur ; that of isotopes heavier than Cl is beta decay to isotopes of argon ; and Cl may decay by either mode to stable S or Ar. Cl occurs in trace quantities in nature as a cosmogenic nuclide in a ratio of about (7–10) × 10 to 1 with stable chlorine isotopes: it

9656-483: The noble gases xenon and radon do not escape fluorination. An impermeable fluoride layer is formed by sodium , magnesium , aluminium , zinc , tin , and silver , which may be removed by heating. Nickel , copper, and steel containers are usually used due to their great resistance to attack by chlorine trifluoride, stemming from the formation of an unreactive layer of metal fluoride. Its reaction with hydrazine to form hydrogen fluoride, nitrogen, and chlorine gases

9798-405: The nuclear binding energy and electron binding energy. For example, the atomic mass of chlorine-35 to five significant digits is 34.969 Da and that of chlorine-37 is 36.966 Da. However, the relative atomic mass of each isotope is quite close to its mass number (always within 1%). The only isotope whose atomic mass is exactly a natural number is C, which has a mass of 12 Da; because

9940-411: The 14 chlorine atoms are formally divalent, and oxidation states are fractional. In addition, all the above chemical regularities are valid for "normal" or close to normal conditions, while at ultra-high pressures (for example, in the cores of large planets), chlorine can exhibit an oxidation state of -3, forming a Na3Cl compound with sodium, which does not fit into traditional concepts of chemistry. Like

10082-543: The 1820s, in France, long before the establishment of the germ theory of disease . This practice was pioneered by Antoine-Germain Labarraque , who adapted Berthollet's "Javel water" bleach and other chlorine preparations. Elemental chlorine has since served a continuous function in topical antisepsis (wound irrigation solutions and the like) and public sanitation, particularly in swimming and drinking water. Chlorine gas

10224-638: The 94 naturally occurring elements, those with atomic numbers 1 through 82 each have at least one stable isotope (except for technetium , element 43 and promethium , element 61, which have no stable isotopes). Isotopes considered stable are those for which no radioactive decay has yet been observed. Elements with atomic numbers 83 through 94 are unstable to the point that radioactive decay of all isotopes can be detected. Some of these elements, notably bismuth (atomic number 83), thorium (atomic number 90), and uranium (atomic number 92), have one or more isotopes with half-lives long enough to survive as remnants of

10366-525: The Earth's crust is in the form of ionic chloride compounds, which includes table salt. It is the second-most abundant halogen (after fluorine) and 20th most abundant element in Earth's crust. These crystal deposits are nevertheless dwarfed by the huge reserves of chloride in seawater. Elemental chlorine is commercially produced from brine by electrolysis , predominantly in the chloralkali process . The high oxidising potential of elemental chlorine led to

10508-487: The French, Italians, Greeks, Portuguese and Poles prefer "azote/azot/azoto" (from roots meaning "no life") for "nitrogen". For purposes of international communication and trade, the official names of the chemical elements both ancient and more recently recognized are decided by the International Union of Pure and Applied Chemistry (IUPAC), which has decided on a sort of international English language, drawing on traditional English names even when an element's chemical symbol

10650-539: The German and Dutch names of oxygen : sauerstoff or zuurstof , both translating into English as acid substance ), so a number of chemists, including Claude Berthollet , suggested that Scheele's dephlogisticated muriatic acid air must be a combination of oxygen and the yet undiscovered element, muriaticum . In 1809, Joseph Louis Gay-Lussac and Louis-Jacques Thénard tried to decompose dephlogisticated muriatic acid air by reacting it with charcoal to release

10792-487: The Greek word χλωρος ( chlōros , "green-yellow"), in reference to its colour. The name " halogen ", meaning "salt producer", was originally used for chlorine in 1811 by Johann Salomo Christoph Schweigger . This term was later used as a generic term to describe all the elements in the chlorine family (fluorine, bromine, iodine), after a suggestion by Jöns Jakob Berzelius in 1826. In 1823, Michael Faraday liquefied chlorine for

10934-756: The Quincy native copper mine of Hancock, Michigan . The world's largest underground salt mine is the Sifto Salt Mine. It produces over 7 million tons of rock salt per year using the room and pillar mining method. It is located half a kilometre under Lake Huron in Ontario , Canada. In the United Kingdom there are three mines; the largest of these is at Winsford in Cheshire , producing, on average, one million tonnes of salt per year. Salt

11076-495: The X 2 molecule (X = Cl, Br, I), ionic radius, and X–X bond length. (Fluorine is anomalous due to its small size.) All four stable halogens experience intermolecular van der Waals forces of attraction, and their strength increases together with the number of electrons among all homonuclear diatomic halogen molecules. Thus, the melting and boiling points of chlorine are intermediate between those of fluorine and bromine: chlorine melts at −101.0 °C and boils at −34.0 °C. As

11218-487: The atomic masses of the elements (their atomic weights or atomic masses) do not always increase monotonically with their atomic numbers. The naming of various substances now known as elements precedes the atomic theory of matter, as names were given locally by various cultures to various minerals, metals, compounds, alloys, mixtures, and other materials, though at the time it was not known which chemicals were elements and which compounds. As they were identified as elements,

11360-602: The central Cl–O bonds, producing the radicals ClO 3 and ClO 4 which immediately decompose to the elements through intermediate oxides. Chlorine forms four oxoacids: hypochlorous acid (HOCl), chlorous acid (HOClO), chloric acid (HOClO 2 ), and perchloric acid (HOClO 3 ). As can be seen from the redox potentials given in the adjacent table, chlorine is much more stable towards disproportionation in acidic solutions than in alkaline solutions: The hypochlorite ions also disproportionate further to produce chloride and chlorate (3 ClO ⇌ 2 Cl + ClO 3 ) but this reaction

11502-413: The chemical substances (di)hydrogen (H 2 ) and (di)oxygen (O 2 ), as H 2 O molecules are different from H 2 and O 2 molecules. For the meaning "chemical substance consisting of a single kind of atoms", the terms "elementary substance" and "simple substance" have been suggested, but they have not gained much acceptance in English chemical literature, whereas in some other languages their equivalent

11644-588: The chloride product is stable to hydrolysis; otherwise, the possibilities include high-temperature oxidative chlorination of the element with chlorine or hydrogen chloride, high-temperature chlorination of a metal oxide or other halide by chlorine, a volatile metal chloride, carbon tetrachloride , or an organic chloride. For instance, zirconium dioxide reacts with chlorine at standard conditions to produce zirconium tetrachloride , and uranium trioxide reacts with hexachloropropene when heated under reflux to give uranium tetrachloride . The second example also involves

11786-424: The chlorine atom is in its lowest (−1) or highest (+7) possible oxidation states. Perchloric acid and aqueous perchlorates are vigorous and sometimes violent oxidising agents when heated, in stark contrast to their mostly inactive nature at room temperature due to the high activation energies for these reactions for kinetic reasons. Perchlorates are made by electrolytically oxidising sodium chlorate, and perchloric acid

11928-544: The chlorine oxyacids increase very quickly as the oxidation state of chlorine increases due to the increasing delocalisation of charge over more and more oxygen atoms in their conjugate bases. Most of the chlorine oxoacids may be produced by exploiting these disproportionation reactions. Hypochlorous acid (HOCl) is highly reactive and quite unstable; its salts are mostly used for their bleaching and sterilising abilities. They are very strong oxidising agents, transferring an oxygen atom to most inorganic species. Chlorous acid (HOClO)

12070-408: The dalton is defined as 1/12 of the mass of a free neutral carbon-12 atom in the ground state. The standard atomic weight (commonly called "atomic weight") of an element is the average of the atomic masses of all the chemical element's isotopes as found in a particular environment, weighted by isotopic abundance, relative to the atomic mass unit. This number may be a fraction that is not close to

12212-429: The dark. Crystalline clathrate hydrates ClO 2 · n H 2 O ( n ≈ 6–10) separate out at low temperatures. However, in the presence of light, these solutions rapidly photodecompose to form a mixture of chloric and hydrochloric acids. Photolysis of individual ClO 2 molecules result in the radicals ClO and ClOO, while at room temperature mostly chlorine, oxygen, and some ClO 3 and Cl 2 O 6 are produced. Cl 2 O 3

12354-421: The deadly effect on insects, the yellow-green colour, and the smell similar to aqua regia . He called it " dephlogisticated muriatic acid air " since it is a gas (then called "airs") and it came from hydrochloric acid (then known as "muriatic acid"). He failed to establish chlorine as an element. Common chemical theory at that time held that an acid is a compound that contains oxygen (remnants of this survive in

12496-575: The delocalisation of the unpaired electron. It explodes above −40 °C as a liquid and under pressure as a gas and therefore must be made at low concentrations for wood-pulp bleaching and water treatment. It is usually prepared by reducing a chlorate as follows: Its production is thus intimately linked to the redox reactions of the chlorine oxoacids. It is a strong oxidising agent, reacting with sulfur , phosphorus , phosphorus halides, and potassium borohydride . It dissolves exothermically in water to form dark-green solutions that very slowly decompose in

12638-574: The development of commercial bleaches and disinfectants , and a reagent for many processes in the chemical industry. Chlorine is used in the manufacture of a wide range of consumer products, about two-thirds of them organic chemicals such as polyvinyl chloride (PVC), many intermediates for the production of plastics , and other end products which do not contain the element. As a common disinfectant, elemental chlorine and chlorine-generating compounds are used more directly in swimming pools to keep them sanitary . Elemental chlorine at high concentration

12780-416: The discovery and use of elements began with early human societies that discovered native minerals like carbon , sulfur , copper and gold (though the modern concept of an element was not yet understood). Attempts to classify materials such as these resulted in the concepts of classical elements , alchemy , and similar theories throughout history. Much of the modern understanding of elements developed from

12922-409: The edges of the cubes simply grow faster than the centers. Halite crystals form very quickly in some rapidly evaporating lakes resulting in modern artifacts with a coating or encrustation of halite crystals. Halite flowers are rare stalactites of curling fibers of halite that are found in certain arid caves of Australia 's Nullarbor Plain . Halite stalactites and encrustations are also reported in

13064-406: The elements are available by name, atomic number, density, melting point, boiling point and chemical symbol , as well as ionization energy . The nuclides of stable and radioactive elements are also available as a list of nuclides , sorted by length of half-life for those that are unstable. One of the most convenient, and certainly the most traditional presentation of the elements, is in the form of

13206-470: The elements are often summarized using the periodic table, which powerfully and elegantly organizes the elements by increasing atomic number into rows ( "periods" ) in which the columns ( "groups" ) share recurring ("periodic") physical and chemical properties. The table contains 118 confirmed elements as of 2021. Although earlier precursors to this presentation exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869, who intended

13348-480: The elements can be uniquely sequenced by atomic number, conventionally from lowest to highest (as in a periodic table), sets of elements are sometimes specified by such notation as "through", "beyond", or "from ... through", as in "through iron", "beyond uranium", or "from lanthanum through lutetium". The terms "light" and "heavy" are sometimes also used informally to indicate relative atomic numbers (not densities), as in "lighter than carbon" or "heavier than lead", though

13490-413: The elements without any stable isotopes are technetium (atomic number 43), promethium (atomic number 61), and all observed elements with atomic number greater than 82. Of the 80 elements with at least one stable isotope, 26 have only one stable isotope. The mean number of stable isotopes for the 80 stable elements is 3.1 stable isotopes per element. The largest number of stable isotopes for a single element

13632-474: The elements, including consideration of their general physical and chemical properties, their states of matter under familiar conditions, their melting and boiling points, their densities, their crystal structures as solids, and their origins. Several terms are commonly used to characterize the general physical and chemical properties of the chemical elements. A first distinction is between metals , which readily conduct electricity , nonmetals , which do not, and

13774-519: The evaporation of seawater or salty lake water. Vast beds of sedimentary evaporite minerals, including halite, can result from the drying up of enclosed lakes and restricted seas. Such salt beds may be hundreds of meters thick and underlie broad areas. Halite occurs at the surface today in playas in regions where evaporation exceeds precipitation such as in the salt flats of Badwater Basin in Death Valley National Park . In

13916-492: The existing names for anciently known elements (e.g., gold, mercury, iron) were kept in most countries. National differences emerged over the element names either for convenience, linguistic niceties, or nationalism. For example, German speakers use "Wasserstoff" (water substance) for "hydrogen", "Sauerstoff" (acid substance) for "oxygen" and "Stickstoff" (smothering substance) for "nitrogen"; English and some other languages use "sodium" for "natrium", and "potassium" for "kalium"; and

14058-630: The explosive stellar nucleosynthesis that produced the heavy metals before the formation of our Solar System . At over 1.9 × 10 years, over a billion times longer than the estimated age of the universe, bismuth-209 has the longest known alpha decay half-life of any isotope, and is almost always considered on par with the 80 stable elements. The heaviest elements (those beyond plutonium, element 94) undergo radioactive decay with half-lives so short that they are not found in nature and must be synthesized . There are now 118 known elements. In this context, "known" means observed well enough, even from just

14200-441: The first time, and demonstrated that what was then known as "solid chlorine" had a structure of chlorine hydrate (Cl 2 ·H 2 O). Chlorine gas was first used by French chemist Claude Berthollet to bleach textiles in 1785. Modern bleaches resulted from further work by Berthollet, who first produced sodium hypochlorite in 1789 in his laboratory in the town of Javel (now part of Paris , France), by passing chlorine gas through

14342-479: The first two. Chlorine has the electron configuration [Ne]3s3p, with the seven electrons in the third and outermost shell acting as its valence electrons . Like all halogens, it is thus one electron short of a full octet, and is hence a strong oxidising agent, reacting with many elements in order to complete its outer shell. Corresponding to periodic trends , it is intermediate in electronegativity between fluorine and bromine (F: 3.98, Cl: 3.16, Br: 2.96, I: 2.66), and

14484-529: The formation of Earth, they are certain to have completely decayed, and if present in novae, are in quantities too small to have been noted. Technetium was the first purportedly non-naturally occurring element synthesized, in 1937, though trace amounts of technetium have since been found in nature (and also the element may have been discovered naturally in 1925). This pattern of artificial production and later natural discovery has been repeated with several other radioactive naturally occurring rare elements. List of

14626-541: The free element muriaticum (and carbon dioxide). They did not succeed and published a report in which they considered the possibility that dephlogisticated muriatic acid air is an element, but were not convinced. In 1810, Sir Humphry Davy tried the same experiment again, and concluded that the substance was an element, and not a compound. He announced his results to the Royal Society on 15 November that year. At that time, he named this new element "chlorine", from

14768-608: The gaseous products were discarded, and hydrogen chloride may have been produced many times before it was discovered that it can be put to chemical use. One of the first such uses was the synthesis of mercury(II) chloride (corrosive sublimate), whose production from the heating of mercury either with alum and ammonium chloride or with vitriol and sodium chloride was first described in the De aluminibus et salibus ("On Alums and Salts", an eleventh- or twelfth century Arabic text falsely attributed to Abu Bakr al-Razi and translated into Latin in

14910-431: The half-lives predicted for the observationally stable lead isotopes range from 10 to 10 years. Elements with atomic numbers 43, 61, and 83 through 94 are unstable enough that their radioactive decay can be detected. Three of these elements, bismuth (element 83), thorium (90), and uranium (92) have one or more isotopes with half-lives long enough to survive as remnants of the explosive stellar nucleosynthesis that produced

15052-399: The heaviest elements also undergo spontaneous fission . Isotopes that are not radioactive, are termed "stable" isotopes. All known stable isotopes occur naturally (see primordial nuclide ). The many radioisotopes that are not found in nature have been characterized after being artificially produced. Certain elements have no stable isotopes and are composed only of radioisotopes: specifically

15194-549: The heavy elements before the formation of the Solar System. For example, at over 1.9 × 10 years, over a billion times longer than the estimated age of the universe, bismuth-209 has the longest known alpha decay half-life of any isotope. The last 24 elements (those beyond plutonium, element 94) undergo radioactive decay with short half-lives and cannot be produced as daughters of longer-lived elements, and thus are not known to occur in nature at all. 1 The properties of

15336-503: The high temperature environment of forest fires, and dioxins have been found in the preserved ashes of lightning-ignited fires that predate synthetic dioxins. In addition, a variety of simple chlorinated hydrocarbons including dichloromethane, chloroform, and carbon tetrachloride have been isolated from marine algae. A majority of the chloromethane in the environment is produced naturally by biological decomposition, forest fires, and volcanoes. Chemical element A chemical element

15478-435: The ice so that it can be easily removed by other means. Also, many cities will spread a mixture of sand and salt on roads during and after a snowstorm to improve traction. Using salt brine is more effective than spreading dry salt because moisture is necessary for the freezing-point depression to work and wet salt sticks to the roads better. Otherwise the salt can be wiped away by traffic. In addition to de-icing, rock salt

15620-454: The laboratory, hydrogen chloride gas may be made by drying the acid with concentrated sulfuric acid. Deuterium chloride, DCl, may be produced by reacting benzoyl chloride with heavy water (D 2 O). At room temperature, hydrogen chloride is a colourless gas, like all the hydrogen halides apart from hydrogen fluoride , since hydrogen cannot form strong hydrogen bonds to the larger electronegative chlorine atom; however, weak hydrogen bonding

15762-462: The minority and stem in each case from one of three causes: extreme inertness and reluctance to participate in chemical reactions (the noble gases , with the exception of xenon in the highly unstable XeCl 2 and XeCl 4 ); extreme nuclear instability hampering chemical investigation before decay and transmutation (many of the heaviest elements beyond bismuth ); and having an electronegativity higher than chlorine's ( oxygen and fluorine ) so that

15904-563: The most reactive chemical compounds known, the list of elements it sets on fire is diverse, containing hydrogen , potassium , phosphorus , arsenic , antimony , sulfur , selenium , tellurium , bromine , iodine , and powdered molybdenum , tungsten , rhodium , iridium , and iron . It will also ignite water, along with many substances which in ordinary circumstances would be considered chemically inert such as asbestos , concrete, glass, and sand. When heated, it will even corrode noble metals as palladium , platinum , and gold , and even

16046-789: The multiple bonds on alkenes and alkynes as well, giving di- or tetrachloro compounds. However, due to the expense and reactivity of chlorine, organochlorine compounds are more commonly produced by using hydrogen chloride, or with chlorinating agents such as phosphorus pentachloride (PCl 5 ) or thionyl chloride (SOCl 2 ). The last is very convenient in the laboratory because all side products are gaseous and do not have to be distilled out. Many organochlorine compounds have been isolated from natural sources ranging from bacteria to humans. Chlorinated organic compounds are found in nearly every class of biomolecules including alkaloids , terpenes , amino acids , flavonoids , steroids , and fatty acids . Organochlorides, including dioxins , are produced in

16188-567: The nature of free chlorine gas as a separate substance was only recognised around 1630 by Jan Baptist van Helmont . Carl Wilhelm Scheele wrote a description of chlorine gas in 1774, supposing it to be an oxide of a new element. In 1809, chemists suggested that the gas might be a pure element, and this was confirmed by Sir Humphry Davy in 1810, who named it after the Ancient Greek χλωρός ( khlōrós , "pale green") because of its colour. Because of its great reactivity, all chlorine in

16330-458: The other carbon–halogen bonds, the C–Cl bond is a common functional group that forms part of core organic chemistry . Formally, compounds with this functional group may be considered organic derivatives of the chloride anion. Due to the difference of electronegativity between chlorine (3.16) and carbon (2.55), the carbon in a C–Cl bond is electron-deficient and thus electrophilic . Chlorination modifies

16472-418: The periodic table, which groups together elements with similar chemical properties (and usually also similar electronic structures). The atomic number of an element is equal to the number of protons in each atom, and defines the element. For example, all carbon atoms contain 6 protons in their atomic nucleus ; so the atomic number of carbon is 6. Carbon atoms may have different numbers of neutrons; atoms of

16614-426: The periodic tables presented here includes: actinides , alkali metals , alkaline earth metals , halogens , lanthanides , transition metals , post-transition metals , metalloids , reactive nonmetals , and noble gases . In this system, the alkali metals, alkaline earth metals, and transition metals, as well as the lanthanides and the actinides, are special groups of the metals viewed in a broader sense. Similarly,

16756-417: The physical properties of hydrocarbons in several ways: chlorocarbons are typically denser than water due to the higher atomic weight of chlorine versus hydrogen, and aliphatic organochlorides are alkylating agents because chloride is a leaving group . Alkanes and aryl alkanes may be chlorinated under free-radical conditions, with UV light. However, the extent of chlorination is difficult to control:

16898-508: The practice of salting the earth was done to make conquered land of an enemy infertile and inhospitable as an act of domination or spite. One biblical reference to this practice is in Judges 9:45 : "he killed the people in it, pulled the wall down and sowed the site with salt." Polyhalite , a mineral fertilizer, is not an NaCl-polymer, but hydrated K 2 Ca 2 Mg- sulfate . Shotgun shells containing rock salt (instead of metal pellets) are

17040-412: The pure element to exist in multiple chemical structures ( spatial arrangements of atoms ), known as allotropes , which differ in their properties. For example, carbon can be found as diamond , which has a tetrahedral structure around each carbon atom; graphite , which has layers of carbon atoms with a hexagonal structure stacked on top of each other; graphene , which is a single layer of graphite that

17182-535: The reaction is not regioselective and often results in a mixture of various isomers with different degrees of chlorination, though this may be permissible if the products are easily separated. Aryl chlorides may be prepared by the Friedel-Crafts halogenation , using chlorine and a Lewis acid catalyst. The haloform reaction , using chlorine and sodium hydroxide , is also able to generate alkyl halides from methyl ketones, and related compounds. Chlorine adds to

17324-772: The reactive nonmetals and the noble gases are nonmetals viewed in the broader sense. In some presentations, the halogens are not distinguished, with astatine identified as a metalloid and the others identified as nonmetals. Another commonly used basic distinction among the elements is their state of matter (phase), whether solid , liquid , or gas , at standard temperature and pressure (STP). Most elements are solids at STP, while several are gases. Only bromine and mercury are liquid at 0 degrees Celsius (32 degrees Fahrenheit) and 1 atmosphere pressure; caesium and gallium are solid at that temperature, but melt at 28.4°C (83.2°F) and 29.8°C (85.6°F), respectively. Melting and boiling points , typically expressed in degrees Celsius at

17466-919: The remaining 11 elements have half lives too short for them to have been present at the beginning of the Solar System, and are therefore considered transient elements. Of these 11 transient elements, five ( polonium , radon , radium , actinium , and protactinium ) are relatively common decay products of thorium and uranium . The remaining six transient elements (technetium, promethium, astatine, francium , neptunium , and plutonium ) occur only rarely, as products of rare decay modes or nuclear reaction processes involving uranium or other heavy elements. Elements with atomic numbers 1 through 82, except 43 (technetium) and 61 (promethium), each have at least one isotope for which no radioactive decay has been observed. Observationally stable isotopes of some elements (such as tungsten and lead ), however, are predicted to be slightly radioactive with very long half-lives: for example,

17608-773: The resultant binary compounds are formally not chlorides but rather oxides or fluorides of chlorine. Even though nitrogen in NCl 3 is bearing a negative charge, the compound is usually called nitrogen trichloride . Chlorination of metals with Cl 2 usually leads to a higher oxidation state than bromination with Br 2 when multiple oxidation states are available, such as in MoCl 5 and MoBr 3 . Chlorides can be made by reaction of an element or its oxide, hydroxide, or carbonate with hydrochloric acid, and then dehydrated by mildly high temperatures combined with either low pressure or anhydrous hydrogen chloride gas. These methods work best when

17750-495: The same element having different numbers of neutrons are known as isotopes of the element. The number of protons in the nucleus also determines its electric charge , which in turn determines the number of electrons of the atom in its non-ionized state. The electrons are placed into atomic orbitals that determine the atom's chemical properties . The number of neutrons in a nucleus usually has very little effect on an element's chemical properties; except for hydrogen (for which

17892-404: The same number of protons in their nucleus), but having different numbers of neutrons . Thus, for example, there are three main isotopes of carbon. All carbon atoms have 6 protons, but they can have either 6, 7, or 8 neutrons. Since the mass numbers of these are 12, 13 and 14 respectively, said three isotopes are known as carbon-12 , carbon-13 , and carbon-14 ( C, C, and C). Natural carbon

18034-457: The second half of the 20th century, physics laboratories became able to produce elements with half-lives too short for an appreciable amount of them to exist at any time. These are also named by IUPAC, which generally adopts the name chosen by the discoverer. This practice can lead to the controversial question of which research group actually discovered an element, a question that delayed the naming of elements with atomic number of 104 and higher for

18176-613: The second half of the twelfth century by Gerard of Cremona , 1144–1187). Another important development was the discovery by pseudo-Geber (in the De inventione veritatis , "On the Discovery of Truth", after c. 1300) that by adding ammonium chloride to nitric acid , a strong solvent capable of dissolving gold (i.e., aqua regia ) could be produced. Although aqua regia is an unstable mixture that continually gives off fumes containing free chlorine gas, this chlorine gas appears to have been ignored until c. 1630, when its nature as

18318-478: The spin magnitude being greater than 1/2 results in non-spherical nuclear charge distribution and thus resonance broadening as a result of a nonzero nuclear quadrupole moment and resultant quadrupolar relaxation. The other chlorine isotopes are all radioactive, with half-lives too short to occur in nature primordially . Of these, the most commonly used in the laboratory are Cl ( t 1/2 = 3.0×10 y) and Cl ( t 1/2 = 37.2 min), which may be produced from

18460-436: The sulfur oxides SO 2 and SO 3 to produce ClSO 2 F and ClOSO 2 F respectively. It will also react exothermically with compounds containing –OH and –NH groups, such as water: Chlorine trifluoride (ClF 3 ) is a volatile colourless molecular liquid which melts at −76.3 °C and boils at 11.8  °C. It may be formed by directly fluorinating gaseous chlorine or chlorine monofluoride at 200–300 °C. One of

18602-474: The surface at high elevation and flows downhill. In these cases, halite is said to be behaving like a rheid . Unusual, purple, fibrous vein-filling halite is found in France and a few other localities. Halite crystals termed hopper crystals appear to be "skeletons" of the typical cubes, with the edges present and stairstep depressions on, or rather in, each crystal face. In a rapidly crystallizing environment,

18744-496: The synthetically produced transuranic elements, available samples have been too small to determine crystal structures. Chemical elements may also be categorized by their origin on Earth, with the first 94 considered naturally occurring, while those with atomic numbers beyond 94 have only been produced artificially via human-made nuclear reactions. Of the 94 naturally occurring elements, 83 are considered primordial and either stable or weakly radioactive. The longest-lived isotopes of

18886-955: The table to illustrate recurring trends in the properties of the elements. The layout of the table has been refined and extended over time as new elements have been discovered and new theoretical models have been developed to explain chemical behavior. Use of the periodic table is now ubiquitous in chemistry, providing an extremely useful framework to classify, systematize and compare all the many different forms of chemical behavior. The table has also found wide application in physics , geology , biology , materials science , engineering , agriculture , medicine , nutrition , environmental health , and astronomy . Its principles are especially important in chemical engineering . The various chemical elements are formally identified by their unique atomic numbers, their accepted names, and their chemical symbols . The known elements have atomic numbers from 1 to 118, conventionally presented as Arabic numerals . Since

19028-585: The thermally unstable FClO to the chemically unreactive perchloryl fluoride (FClO 3 ), the other three being FClO 2 , F 3 ClO, and F 3 ClO 2 . All five behave similarly to the chlorine fluorides, both structurally and chemically, and may act as Lewis acids or bases by gaining or losing fluoride ions respectively or as very strong oxidising and fluorinating agents. The chlorine oxides are well-studied in spite of their instability (all of them are endothermic compounds). They are important because they are produced when chlorofluorocarbons undergo photolysis in

19170-497: The third-highest electronegativity on the revised Pauling scale , behind only oxygen and fluorine. Chlorine played an important role in the experiments conducted by medieval alchemists , which commonly involved the heating of chloride salts like ammonium chloride ( sal ammoniac ) and sodium chloride ( common salt ), producing various chemical substances containing chlorine such as hydrogen chloride , mercury(II) chloride (corrosive sublimate), and aqua regia . However,

19312-621: The universe at large, in the spectra of stars and also supernovae, where short-lived radioactive elements are newly being made. The first 94 elements have been detected directly on Earth as primordial nuclides present from the formation of the Solar System , or as naturally occurring fission or transmutation products of uranium and thorium. The remaining 24 heavier elements, not found today either on Earth or in astronomical spectra, have been produced artificially: all are radioactive, with short half-lives; if any of these elements were present at

19454-405: The upper atmosphere and cause the destruction of the ozone layer. None of them can be made from directly reacting the elements. Dichlorine monoxide (Cl 2 O) is a brownish-yellow gas (red-brown when solid or liquid) which may be obtained by reacting chlorine gas with yellow mercury(II) oxide . It is very soluble in water, in which it is in equilibrium with hypochlorous acid (HOCl), of which it

19596-524: The weight of the overlying rock. Salt domes contain anhydrite , gypsum , and native sulfur , in addition to halite and sylvite . They are common along the Gulf coasts of Texas and Louisiana and are often associated with petroleum deposits. Germany , Spain , the Netherlands , Denmark , Romania and Iran also have salt domes. Salt glaciers exist in arid Iran where the salt has broken through

19738-528: The work of Dmitri Mendeleev , a Russian chemist who published the first recognizable periodic table in 1869. This table organizes the elements by increasing atomic number into rows (" periods ") in which the columns (" groups ") share recurring ("periodic") physical and chemical properties . The periodic table summarizes various properties of the elements, allowing chemists to derive relationships between them and to make predictions about elements not yet discovered, and potential new compounds. By November 2016,

19880-565: Was first used as a weapon on April 22, 1915, at the Second Battle of Ypres by the German Army . The effect on the allies was devastating because the existing gas masks were difficult to deploy and had not been broadly distributed. Chlorine is the second halogen , being a nonmetal in group 17 of the periodic table. Its properties are thus similar to fluorine , bromine , and iodine , and are largely intermediate between those of

20022-626: Was used as early as 3000 BC and brine as early as 6000 BC. Around 900, the authors of the Arabic writings attributed to Jabir ibn Hayyan (Latin: Geber) and the Persian physician and alchemist Abu Bakr al-Razi ( c. 865–925, Latin: Rhazes) were experimenting with sal ammoniac ( ammonium chloride ), which when it was distilled together with vitriol (hydrated sulfates of various metals) produced hydrogen chloride . However, it appears that in these early experiments with chloride salts ,

20164-433: Was used in experimental rocket engine, but has problems largely stemming from its extreme hypergolicity resulting in ignition without any measurable delay. Today, it is mostly used in nuclear fuel processing, to oxidise uranium to uranium hexafluoride for its enriching and to separate it from plutonium , as well as in the semiconductor industry, where it is used to clean chemical vapor deposition chambers. It can act as

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