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90-492: In chemistry , there are three definitions in common use of the word " base ": Arrhenius bases , Brønsted bases , and Lewis bases . All definitions agree that bases are substances that react with acids , as originally proposed by G.-F. Rouelle in the mid-18th century. In 1884, Svante Arrhenius proposed that a base is a substance which dissociates in aqueous solution to form hydroxide ions OH. These ions can react with hydrogen ions (H according to Arrhenius) from

180-777: A boiling point of −100.3 °C and a critical temperature of −12.3 °C, so that it can be stored as a refrigerated liquid only between those temperatures. Storage or transport vessels should be designed to withstand internal pressure, since a refrigeration system failure could cause pressures to rise to the critical pressure of 49.85 bar (4.985 MPa). Boron trifluoride is corrosive. Suitable metals for equipment handling boron trifluoride include stainless steel , monel , and hastelloy . In presence of moisture it corrodes steel, including stainless steel. It reacts with polyamides . Polytetrafluoroethylene , polychlorotrifluoroethylene , polyvinylidene fluoride , and polypropylene show satisfactory resistance. The grease used in

270-440: A chemical equation . While in a non-nuclear chemical reaction the number and kind of atoms on both sides of the equation are equal, for a nuclear reaction this holds true only for the nuclear particles viz. protons and neutrons. The sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its mechanism . A chemical reaction can be envisioned to take place in

360-505: A base is also called the acidity of the base. On the basis of acidity bases can be classified into three types: monoacidic, diacidic and triacidic. When one molecule of a base via complete ionization produces one hydroxide ion, the base is said to be a monoacidic or monoprotic base. Examples of monoacidic bases are: Sodium hydroxide , potassium hydroxide , silver hydroxide , ammonium hydroxide , etc. When one molecule of base via complete ionization produces two hydroxide ions,

450-598: A bond with a proton due to the unshared pair of electrons that the bases possess. In the Lewis theory , a base is an electron pair donor which can share a pair of electrons with an electron acceptor which is described as a Lewis acid. The Lewis theory is more general than the Brønsted model because the Lewis acid is not necessarily a proton, but can be another molecule (or ion) with a vacant low-lying orbital which can accept

540-467: A chemical reaction is said to have occurred. A chemical reaction is therefore a concept related to the "reaction" of a substance when it comes in close contact with another, whether as a mixture or a solution ; exposure to some form of energy, or both. It results in some energy exchange between the constituents of the reaction as well as with the system environment, which may be designed vessels—often laboratory glassware . Chemical reactions can result in

630-470: A chemical transformation is the rearrangement of electrons in the chemical bonds between atoms. It can be symbolically depicted through a chemical equation , which usually involves atoms as subjects. The number of atoms on the left and the right in the equation for a chemical transformation is equal. (When the number of atoms on either side is unequal, the transformation is referred to as a nuclear reaction or radioactive decay .) The type of chemical reactions

720-498: A conjugate base by absorbing an electrically neutral acid, basic strength of the surface is determined. The "number of basic sites per unit surface area of the solid" is used to express how much basic strength is found on a solid base catalyst. Scientists have developed two methods to measure the amount of basic sites: one, titration with benzoic acid using indicators and gaseous acid adsorption. A solid with enough basic strength will absorb an electrically neutral acidic indicator and cause

810-412: A dense core called the atomic nucleus surrounded by a space occupied by an electron cloud . The nucleus is made up of positively charged protons and uncharged neutrons (together called nucleons ), while the electron cloud consists of negatively charged electrons which orbit the nucleus. In a neutral atom, the negatively charged electrons balance out the positive charge of the protons. The nucleus

900-535: A directed beam in a vacuum in a mass spectrometer . Charged polyatomic collections residing in solids (for example, common sulfate or nitrate ions) are generally not considered "molecules" in chemistry. Some molecules contain one or more unpaired electrons, creating radicals . Most radicals are comparatively reactive, but some, such as nitric oxide (NO) can be stable. The "inert" or noble gas elements ( helium , neon , argon , krypton , xenon and radon ) are composed of lone atoms as their smallest discrete unit, but

990-801: A fundamental level. For example, chemistry explains aspects of plant growth ( botany ), the formation of igneous rocks ( geology ), how atmospheric ozone is formed and how environmental pollutants are degraded ( ecology ), the properties of the soil on the Moon ( cosmochemistry ), how medications work ( pharmacology ), and how to collect DNA evidence at a crime scene ( forensics ). Chemistry has existed under various names since ancient times. It has evolved, and now chemistry encompasses various areas of specialisation, or subdisciplines, that continue to increase in number and interrelate to create further interdisciplinary fields of study. The applications of various fields of chemistry are used frequently for economic purposes in

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1080-418: A hydroxide ion but nevertheless react with water, resulting in an increase in the concentration of hydroxide ion. Also, some non-aqueous solvents contain Brønsted bases which react with solvated protons. For example, in liquid ammonia , NH 2 is the basic ion species which accepts protons from NH 4 , the acidic species in this solvent. G. N. Lewis realized that water, ammonia, and other bases can form

1170-411: A number of steps, each of which may have a different speed. Many reaction intermediates with variable stability can thus be envisaged during the course of a reaction. Reaction mechanisms are proposed to explain the kinetics and the relative product mix of a reaction. Many physical chemists specialize in exploring and proposing the mechanisms of various chemical reactions. Several empirical rules, like

1260-448: A p K a of more than about 13 are considered very weak, and their conjugate bases are strong bases. Group 1 salts of carbanions , amide ions , and hydrides tend to be even stronger bases due to the extreme weakness of their conjugate acids, which are stable hydrocarbons, amines, and dihydrogen. Usually, these bases are created by adding pure alkali metals such as sodium into the conjugate acid. They are called superbases , and it

1350-905: A pair of electrons. One notable example is boron trifluoride (BF 3 ). Some other definitions of both bases and acids have been proposed in the past, but are not commonly used today. General properties of bases include: The following reaction represents the general reaction between a base (B) and water to produce a conjugate acid (BH) and a conjugate base (OH): B ( aq ) + H 2 O ( l ) ↽ − − ⇀ BH + ( aq ) + OH − ( aq ) {\displaystyle {\ce {{B}_{(aq)}+ {H2O}_{(l)}<=> {BH+}_{(aq)}+ {OH- }_{(aq)}}}} The equilibrium constant, K b , for this reaction can be found using

1440-424: A particular substance per volume of solution , and is commonly reported in mol/ dm . In addition to the specific chemical properties that distinguish different chemical classifications, chemicals can exist in several phases. For the most part, the chemical classifications are independent of these bulk phase classifications; however, some more exotic phases are incompatible with certain chemical properties. A phase

1530-413: A positive hydrogen ion to another substance in a chemical reaction; by extension, a base is the substance which receives that hydrogen ion. Boron trifluoride The geometry of a molecule of BF 3 is trigonal planar . Its D 3h symmetry conforms with the prediction of VSEPR theory . The molecule has no dipole moment by virtue of its high symmetry. The molecule is isoelectronic with

1620-405: A pure chemical substance that has its unique set of chemical properties, that is, its potential to undergo a certain set of chemical reactions with other substances. However, this definition only works well for substances that are composed of molecules, which is not true of many substances (see below). Molecules are typically a set of atoms bound together by covalent bonds , such that the structure

1710-609: A substance may undergo and the energy changes that may accompany it are constrained by certain basic rules, known as chemical laws . Energy and entropy considerations are invariably important in almost all chemical studies. Chemical substances are classified in terms of their structure , phase, as well as their chemical compositions . They can be analyzed using the tools of chemical analysis , e.g. spectroscopy and chromatography . Scientists engaged in chemical research are known as chemists . Most chemists specialize in one or more sub-disciplines. Several concepts are essential for

1800-462: A violent exothermic reaction, and the base itself can cause just as much damage as the original acid spill. Bases are generally compounds that can neutralize an amount of acid. Both sodium carbonate and ammonia are bases, although neither of these substances contains OH groups. Both compounds accept H when dissolved in protic solvents such as water: From this, a pH , or acidity, can be calculated for aqueous solutions of bases. A base

1890-583: A water solution due to the acidity of water. Resonance stabilization, however, enables weaker bases such as carboxylates; for example, sodium acetate is a weak base . A strong base is a basic chemical compound that can remove a proton (H) from (or deprotonate ) a molecule of even a very weak acid (such as water) in an acid–base reaction. Common examples of strong bases include hydroxides of alkali metals and alkaline earth metals, like NaOH and Ca(OH) 2 , respectively. Due to their low solubility, some bases, such as alkaline earth hydroxides, can be used when

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1980-420: Is a conveniently handled liquid and consequently is widely encountered as a laboratory source of BF 3 . Another common adduct is the adduct with dimethyl sulfide ( BF 3 ·S(CH 3 ) 2 ), which can be handled as a neat liquid. All three lighter boron trihalides, BX 3 (X = F, Cl, Br) form stable adducts with common Lewis bases. Their relative Lewis acidities can be evaluated in terms of

2070-460: Is a list of several strong bases: The cations of these strong bases appear in the first and second groups of the periodic table (alkali and earth alkali metals). Tetraalkylated ammonium hydroxides are also strong bases since they dissociate completely in water. Guanidine is a special case of a species that is exceptionally stable when protonated, analogously to the reason that makes perchloric acid and sulfuric acid very strong acids. Acids with

2160-414: Is a pure substance which is composed of a single type of atom, characterized by its particular number of protons in the nuclei of its atoms, known as the atomic number and represented by the symbol Z . The mass number is the sum of the number of protons and neutrons in a nucleus. Although all the nuclei of all atoms belonging to one element will have the same atomic number, they may not necessarily have

2250-409: Is a set of states of a chemical system that have similar bulk structural properties, over a range of conditions, such as pressure or temperature . Physical properties, such as density and refractive index tend to fall within values characteristic of the phase. The phase of matter is defined by the phase transition , which is when energy put into or taken out of the system goes into rearranging

2340-586: Is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics . A reaction is feasible only if the total change in the Gibbs free energy is negative, Δ G ≤ 0 {\displaystyle \Delta G\leq 0\,} ; if it is equal to zero the chemical reaction is said to be at equilibrium . There exist only limited possible states of energy for electrons, atoms and molecules. These are determined by

2430-663: Is also defined as a molecule that has the ability to accept an electron pair bond by entering another atom's valence shell through its possession of one electron pair. There are a limited number of elements that have atoms with the ability to provide a molecule with basic properties. Carbon can act as a base as well as nitrogen and oxygen . Fluorine and sometimes rare gases possess this ability as well. This occurs typically in compounds such as butyl lithium , alkoxides , and metal amides such as sodium amide . Bases of carbon, nitrogen and oxygen without resonance stabilization are usually very strong, or superbases , which cannot exist in

2520-422: Is also possible to define analogs in two-dimensional systems, which has received attention for its relevance to systems in biology . Atoms sticking together in molecules or crystals are said to be bonded with one another. A chemical bond may be visualized as the multipole balance between the positive charges in the nuclei and the negative charges oscillating about them. More than simple attraction and repulsion,

2610-439: Is also used to identify the composition of remote objects – like stars and distant galaxies – by analyzing their radiation spectra. The term chemical energy is often used to indicate the potential of a chemical substance to undergo a transformation through a chemical reaction or to transform other chemical substances. When a chemical substance is transformed as a result of its interaction with another substance or with energy,

2700-464: Is called a mixture. Examples of mixtures are air and alloys . The mole is a unit of measurement that denotes an amount of substance (also called chemical amount). One mole is defined to contain exactly 6.022 140 76 × 10 particles ( atoms , molecules , ions , or electrons ), where the number of particles per mole is known as the Avogadro constant . Molar concentration is the amount of

2790-523: Is composed of gaseous matter that has been completely ionized, usually through high temperature. A substance can often be classified as an acid or a base . There are several different theories which explain acid–base behavior. The simplest is Arrhenius theory , which states that acid is a substance that produces hydronium ions when it is dissolved in water, and a base is one that produces hydroxide ions when dissolved in water. According to Brønsted–Lowry acid–base theory , acids are substances that donate

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2880-472: Is dense; the mass of a nucleon is approximately 1,836 times that of an electron, yet the radius of an atom is about 10,000 times that of its nucleus. The atom is also the smallest entity that can be envisaged to retain the chemical properties of the element, such as electronegativity , ionization potential , preferred oxidation state (s), coordination number , and preferred types of bonds to form (e.g., metallic , ionic , covalent ). A chemical element

2970-464: Is electrically neutral and all valence electrons are paired with other electrons either in bonds or in lone pairs . Thus, molecules exist as electrically neutral units, unlike ions. When this rule is broken, giving the "molecule" a charge, the result is sometimes named a molecular ion or a polyatomic ion. However, the discrete and separate nature of the molecular concept usually requires that molecular ions be present only in well-separated form, such as

3060-447: Is impossible to keep them in aqueous solutions because they are stronger bases than the hydroxide ion (See the leveling effect .) For example, the ethoxide ion (conjugate base of ethanol) undergoes this reaction quantitatively in presence of water. Examples of common superbases are: Strongest superbases are synthesised in only gas phase: A weak base is one which does not fully ionize in an aqueous solution , or in which protonation

3150-712: Is incomplete. For example, ammonia transfers a proton to water according to the equation The equilibrium constant for this reaction at 25 °C is 1.8 x 10, such that the extent of reaction or degree of ionization is quite small. A Lewis base or electron-pair donor is a molecule with one or more high-energy lone pairs of electrons which can be shared with a low-energy vacant orbital in an acceptor molecule to form an adduct . In addition to H, possible electron-pair acceptors (Lewis acids) include neutral molecules such as BF 3 and high oxidation state metal ions such as Ag, Fe and Mn. Adducts involving metal ions are usually described as coordination complexes . According to

3240-537: Is more easily transferred between substances relative to light or other forms of electronic energy. For example, ultraviolet electromagnetic radiation is not transferred with as much efficacy from one substance to another as thermal or electrical energy. The existence of characteristic energy levels for different chemical substances is useful for their identification by the analysis of spectral lines . Different kinds of spectra are often used in chemical spectroscopy , e.g. IR , microwave , NMR , ESR , etc. Spectroscopy

3330-464: Is that the F atom is small compared to the larger Cl and Br atoms. As a consequence, the bond length between boron and the halogen increases while going from fluorine to iodine hence spatial overlap between the orbitals becomes more difficult. The lone pair electron in p z of F is readily and easily donated and overlapped to empty p z orbital of boron. As a result, the pi donation of F is greater than that of Cl or Br. In an alternative explanation,

3420-468: Is the crystal structure , or arrangement, of the atoms. Another phase commonly encountered in the study of chemistry is the aqueous phase, which is the state of substances dissolved in aqueous solution (that is, in water). Less familiar phases include plasmas , Bose–Einstein condensates and fermionic condensates and the paramagnetic and ferromagnetic phases of magnetic materials. While most familiar phases deal with three-dimensional systems, it

3510-458: Is the quantum mechanical model . Traditional chemistry starts with the study of elementary particles , atoms , molecules , substances , metals , crystals and other aggregates of matter . Matter can be studied in solid, liquid, gas and plasma states , in isolation or in combination. The interactions, reactions and transformations that are studied in chemistry are usually the result of interactions between atoms, leading to rearrangements of

3600-507: Is the probability of a molecule to have energy greater than or equal to E at the given temperature T. This exponential dependence of a reaction rate on temperature is known as the Arrhenius equation . The activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound . A related concept free energy , which also incorporates entropy considerations,

3690-526: Is useful in identifying periodic trends . A compound is a pure chemical substance composed of more than one element. The properties of a compound bear little similarity to those of its elements. The standard nomenclature of compounds is set by the International Union of Pure and Applied Chemistry (IUPAC). Organic compounds are named according to the organic nomenclature system. The names for inorganic compounds are created according to

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3780-422: Is usually produced in situ using boron trifluoride etherate , which is a commercially available liquid. Laboratory routes to the solvent-free materials are numerous. A well documented route involves the thermal decomposition of diazonium salts of [BF 4 ] : Alternatively it arises from the reaction of sodium tetrafluoroborate , boron trioxide , and sulfuric acid : Anhydrous boron trifluoride has

3870-509: The Woodward–Hoffmann rules often come in handy while proposing a mechanism for a chemical reaction. According to the IUPAC gold book, a chemical reaction is "a process that results in the interconversion of chemical species." Accordingly, a chemical reaction may be an elementary reaction or a stepwise reaction . An additional caveat is made, in that this definition includes cases where

3960-455: The chemical bonds which hold atoms together. Such behaviors are studied in a chemistry laboratory . The chemistry laboratory stereotypically uses various forms of laboratory glassware . However glassware is not central to chemistry, and a great deal of experimental (as well as applied/industrial) chemistry is done without it. A chemical reaction is a transformation of some substances into one or more different substances. The basis of such

4050-493: The chemical industry . The word chemistry comes from a modification during the Renaissance of the word alchemy , which referred to an earlier set of practices that encompassed elements of chemistry, metallurgy , philosophy , astrology , astronomy , mysticism , and medicine . Alchemy is often associated with the quest to turn lead or other base metals into gold, though alchemists were also interested in many of

4140-469: The duet rule , and in this way they are reaching the electron configuration of the noble gas helium , which has two electrons in its outer shell. Similarly, theories from classical physics can be used to predict many ionic structures. With more complicated compounds, such as metal complexes , valence bond theory is less applicable and alternative approaches, such as the molecular orbital theory, are generally used. See diagram on electronic orbitals. In

4230-510: The inorganic nomenclature system. When a compound has more than one component, then they are divided into two classes, the electropositive and the electronegative components. In addition the Chemical Abstracts Service has devised a method to index chemical substances. In this scheme each chemical substance is identifiable by a number known as its CAS registry number . A molecule is the smallest indivisible portion of

4320-500: The interconversion of conformers is experimentally observable. Such detectable chemical reactions normally involve sets of molecular entities as indicated by this definition, but it is often conceptually convenient to use the term also for changes involving single molecular entities (i.e. 'microscopic chemical events'). An ion is a charged species, an atom or a molecule, that has lost or gained one or more electrons. When an atom loses an electron and thus has more protons than electrons,

4410-529: The intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water (H 2 O); a liquid at room temperature because its molecules are bound by hydrogen bonds . Whereas hydrogen sulfide (H 2 S) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole–dipole interactions . The transfer of energy from one chemical substance to another depends on

4500-438: The size of energy quanta emitted from one substance. However, heat energy is often transferred more easily from almost any substance to another because the phonons responsible for vibrational and rotational energy levels in a substance have much less energy than photons invoked for the electronic energy transfer. Thus, because vibrational and rotational energy levels are more closely spaced than electronic energy levels, heat

4590-564: The French chemist, Guillaume-François Rouelle . ... In 1754 Rouelle explicitly defined a neutral salt as the product formed by the union of an acid with any substance, be it a water-soluble alkali, a volatile alkali, an absorbent earth, a metal, or an oil, capable of serving as "a base" for the salt "by giving it a concrete or solid form." Most acids known in the 18th century were volatile liquids or "spirits" capable of distillation, whereas salts, by their very nature, were crystalline solids. Hence it

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4680-420: The French chemist, Louis Lémery , as a synonym for the older Paracelsian term "matrix." In keeping with 16th-century animism , Paracelsus had postulated that naturally occurring salts grew within the earth as a result of a universal acid or seminal principle having impregnated an earthy matrix or womb. ... Its modern meaning and general introduction into the chemical vocabulary, however, is usually attributed to

4770-515: The Valence Shell Electron Pair Repulsion model ( VSEPR ), and the concept of oxidation number can be used to explain molecular structure and composition. An ionic bond is formed when a metal loses one or more of its electrons, becoming a positively charged cation, and the electrons are then gained by the non-metal atom, becoming a negatively charged anion. The two oppositely charged ions attract one another, and

4860-633: The acidic indicator's color to change to the color of its conjugate base. When performing the gaseous acid adsorption method, nitric oxide is used. The basic sites are then determined by calculating the amount of carbon dioxide that is absorbed. Basic substances can be used as insoluble heterogeneous catalysts for chemical reactions . Some examples are metal oxides such as magnesium oxide , calcium oxide , and barium oxide as well as potassium fluoride on alumina and some zeolites . Many transition metals make good catalysts, many of which form basic substances. Basic catalysts are used for hydrogenation ,

4950-494: The atom is a positively charged ion or cation . When an atom gains an electron and thus has more electrons than protons, the atom is a negatively charged ion or anion . Cations and anions can form a crystalline lattice of neutral salts , such as the Na and Cl ions forming sodium chloride , or NaCl. Examples of polyatomic ions that do not split up during acid–base reactions are hydroxide (OH ) and phosphate (PO 4 ). Plasma

5040-632: The base is said to be diacidic or diprotic . Examples of diacidic bases are: Barium hydroxide , magnesium hydroxide , calcium hydroxide , zinc hydroxide , iron(II) hydroxide , tin(II) hydroxide , lead(II) hydroxide , copper(II) hydroxide , etc. When one molecule of base via complete ionization produces three hydroxide ions, the base is said to be triacidic or triprotic . Examples of triacidic bases are: Aluminium hydroxide , ferrous hydroxide , Gold Trihydroxide , The concept of base stems from an older alchemical notion of "the matrix": The term "base" appears to have been first used in 1717 by

5130-472: The carbonate anion, CO 2− 3 . BF 3 is commonly referred to as " electron deficient ," a description that is reinforced by its exothermic reactivity toward Lewis bases . In the boron trihalides, BX 3 , the length of the B–X bonds (1.30 Å) is shorter than would be expected for single bonds, and this shortness may indicate stronger B–X π-bonding in the fluoride. A facile explanation invokes

5220-411: The changes they undergo during reactions with other substances . Chemistry also addresses the nature of chemical bonds in chemical compounds . In the scope of its subject, chemistry occupies an intermediate position between physics and biology . It is sometimes called the central science because it provides a foundation for understanding both basic and applied scientific disciplines at

5310-412: The context of chemistry, energy is an attribute of a substance as a consequence of its atomic , molecular or aggregate structure . Since a chemical transformation is accompanied by a change in one or more of these kinds of structures, it is invariably accompanied by an increase or decrease of energy of the substances involved. Some energy is transferred between the surroundings and the reactants of

5400-452: The dissociation of acids to form water in an acid–base reaction . A base was therefore a metal hydroxide such as NaOH or Ca(OH) 2 . Such aqueous hydroxide solutions were also described by certain characteristic properties. They are slippery to the touch, can taste bitter and change the color of pH indicators (e.g., turn red litmus paper blue). In water, by altering the autoionization equilibrium , bases yield solutions in which

5490-424: The effect of an acid is to increase the hydronium (H 3 O) concentration in water, whereas bases reduce this concentration. A reaction between aqueous solutions of an acid and a base is called neutralization , producing a solution of water and a salt in which the salt separates into its component ions. If the aqueous solution is saturated with a given salt solute , any additional such salt precipitates out of

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5580-429: The energies and distributions characterize the availability of an electron to bond to another atom. The chemical bond can be a covalent bond , an ionic bond , a hydrogen bond or just because of Van der Waals force . Each of these kinds of bonds is ascribed to some potential. These potentials create the interactions which hold atoms together in molecules or crystals . In many simple compounds, valence bond theory ,

5670-695: The equipment should be fluorocarbon based, as boron trifluoride reacts with the hydrocarbon-based ones. Unlike the aluminium and gallium trihalides, the boron trihalides are all monomeric . They undergo rapid halide exchange reactions: Because of the facility of this exchange process, the mixed halides cannot be obtained in pure form. Boron trifluoride is a versatile Lewis acid that forms adducts with such Lewis bases as fluoride and ethers : Tetrafluoroborate salts are commonly employed as non-coordinating anions . The adduct with diethyl ether , boron trifluoride diethyl etherate, or just boron trifluoride etherate , ( BF 3 ·O(CH 2 CH 3 ) 2 )

5760-423: The following general equation: In this equation, the base (B) and the extremely strong base (the conjugate base OH) compete for the proton. As a result, bases that react with water have relatively small equilibrium constant values. The base is weaker when it has a lower equilibrium constant value. Bases react with acids to neutralize each other at a fast rate both in water and in alcohol. When dissolved in water,

5850-444: The formation or dissociation of molecules, that is, molecules breaking apart to form two or more molecules or rearrangement of atoms within or across molecules. Chemical reactions usually involve the making or breaking of chemical bonds. Oxidation, reduction , dissociation , acid–base neutralization and molecular rearrangement are some examples of common chemical reactions. A chemical reaction can be symbolically depicted through

5940-402: The high acidity of fluoroboric acid, the fluoroborate ion can be used to isolate particularly electrophilic cations, such as diazonium ions, that are otherwise difficult to isolate as solids. Boron trifluoride is most importantly used as a reagent in organic synthesis , typically as a Lewis acid . Examples include: Other, less common uses for boron trifluoride include: Boron trifluoride

6030-399: The hydrogen ion activity is lower than it is in pure water, i.e., the water has a pH higher than 7.0 at standard conditions. A soluble base is called an alkali if it contains and releases OH ions quantitatively . Metal oxides , hydroxides , and especially alkoxides are basic, and conjugate bases of weak acids are weak bases. Bases and acids are seen as chemical opposites because

6120-445: The ionic bond is the electrostatic force of attraction between them. For example, sodium (Na), a metal, loses one electron to become an Na cation while chlorine (Cl), a non-metal, gains this electron to become Cl . The ions are held together due to electrostatic attraction, and that compound sodium chloride (NaCl), or common table salt, is formed. In a covalent bond, one or more pairs of valence electrons are shared by two atoms:

6210-436: The low Lewis acidity for BF 3 is attributed to the relative weakness of the bond in the adducts F 3 B−L . Yet another explanation might be found in the fact that the p z orbitals in each higher period have an extra nodal plane and opposite signs of the wave function on each side of that plane. This results in bonding and antibonding regions within the same bond, diminishing the effective overlap and so lowering

6300-473: The main characteristics of a molecule is its geometry often called its structure . While the structure of diatomic, triatomic or tetra-atomic molecules may be trivial, (linear, angular pyramidal etc.) the structure of polyatomic molecules, that are constituted of more than six atoms (of several elements) can be crucial for its chemical nature. A chemical substance is a kind of matter with a definite composition and set of properties . A collection of substances

6390-616: The migration of double bonds , in the Meerwein-Ponndorf-Verley reduction , the Michael reaction , and many others. Both CaO and BaO can be highly active catalysts if they are heated to high temperatures. Bases with only one ionizable hydroxide (OH) ion per formula unit are called monoprotic since they can accept one proton (H). Bases with more than one OH- per formula unit are polyprotic . The number of ionizable hydroxide (OH) ions present in one formula unit of

6480-420: The original formulation of Lewis , when a neutral base forms a bond with a neutral acid, a condition of electric stress occurs. The acid and the base share the electron pair that formerly belonged to the base. As a result, a high dipole moment is created, which can only be decreased to zero by rearranging the molecules. Examples of solid bases include: Depending on a solid surface's ability to successfully form

6570-419: The other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. Identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals . However, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up

6660-631: The questions of modern chemistry. The modern word alchemy in turn is derived from the Arabic word al-kīmīā ( الكیمیاء ). This may have Egyptian origins since al-kīmīā is derived from the Ancient Greek χημία , which is in turn derived from the word Kemet , which is the ancient name of Egypt in the Egyptian language. Alternately, al-kīmīā may derive from χημεία 'cast together'. The current model of atomic structure

6750-478: The reaction absorbs heat from the surroundings. Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy . The speed of a chemical reaction (at given temperature T) is related to the activation energy E, by the Boltzmann's population factor e − E / k T {\displaystyle e^{-E/kT}} – that

6840-433: The reaction in the form of heat or light ; thus the products of a reaction may have more or less energy than the reactants. A reaction is said to be exergonic if the final state is lower on the energy scale than the initial state; in the case of endergonic reactions the situation is the reverse. A reaction is said to be exothermic if the reaction releases heat to the surroundings; in the case of endothermic reactions ,

6930-484: The relative exothermicities of the adduct-forming reaction. Such measurements have revealed the following sequence for the Lewis acidity: This trend is commonly attributed to the degree of π-bonding in the planar boron trihalide that would be lost upon pyramidalization of the BX 3 molecule. which follows this trend: The criteria for evaluating the relative strength of π-bonding are not clear, however. One suggestion

7020-544: The resulting electrically neutral group of bonded atoms is termed a molecule . Atoms will share valence electrons in such a way as to create a noble gas electron configuration (eight electrons in their outermost shell) for each atom. Atoms that tend to combine in such a way that they each have eight electrons in their valence shell are said to follow the octet rule . However, some elements like hydrogen and lithium need only two electrons in their outermost shell to attain this stable configuration; these atoms are said to follow

7110-403: The rules of quantum mechanics , which require quantization of energy of a bound system. The atoms/molecules in a higher energy state are said to be excited. The molecules/atoms of substance in an excited energy state are often much more reactive; that is, more amenable to chemical reactions. The phase of a substance is invariably determined by its energy and the energy of its surroundings. When

7200-418: The salts dissolve, the stomach acid reacts with the hydroxide produced by the suspensions. Strong bases hydrolyze in water almost completely, resulting in the leveling effect ." In this process, the water molecule combines with a strong base, due to the water's amphoteric ability; and, a hydroxide ion is released. Very strong bases can even deprotonate very weakly acidic C–H groups in the absence of water. Here

7290-474: The same mass number; atoms of an element which have different mass numbers are known as isotopes . For example, all atoms with 6 protons in their nuclei are atoms of the chemical element carbon , but atoms of carbon may have mass numbers of 12 or 13. The standard presentation of the chemical elements is in the periodic table , which orders elements by atomic number. The periodic table is arranged in groups , or columns, and periods , or rows. The periodic table

7380-645: The solid crust, mantle, and core of the Earth are chemical compounds without molecules. These other types of substances, such as ionic compounds and network solids , are organized in such a way as to lack the existence of identifiable molecules per se . Instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. Examples of such substances are mineral salts (such as table salt ), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. One of

7470-414: The solubility factor is not taken into account. One advantage of this low solubility is that "many antacids were suspensions of metal hydroxides such as aluminium hydroxide and magnesium hydroxide"; compounds with low solubility and the ability to stop an increase in the concentration of the hydroxide ion, preventing the harm of the tissues in the mouth, oesophagus, and stomach. As the reaction continues and

7560-487: The solution. In the more general Brønsted–Lowry acid–base theory (1923), a base is a substance that can accept hydrogen cations (H)—otherwise known as protons . This does include aqueous hydroxides since OH does react with H to form water, so that Arrhenius bases are a subset of Brønsted bases. However, there are also other Brønsted bases which accept protons, such as aqueous solutions of ammonia (NH 3 ) or its organic derivatives ( amines ). These bases do not contain

7650-635: The strong base sodium hydroxide ionizes into hydroxide and sodium ions: and similarly, in water the acid hydrogen chloride forms hydronium and chloride ions: When the two solutions are mixed, the H 3 O and OH ions combine to form water molecules: If equal quantities of NaOH and HCl are dissolved, the base and the acid neutralize exactly, leaving only NaCl, effectively table salt , in solution. Weak bases, such as baking soda or egg white, should be used to neutralize any acid spills. Neutralizing acid spills with strong bases, such as sodium hydroxide or potassium hydroxide , can cause

7740-695: The structure of the system, instead of changing the bulk conditions. Sometimes the distinction between phases can be continuous instead of having a discrete boundary' in this case the matter is considered to be in a supercritical state. When three states meet based on the conditions, it is known as a triple point and since this is invariant, it is a convenient way to define a set of conditions. The most familiar examples of phases are solids , liquids , and gases . Many substances exhibit multiple solid phases. For example, there are three phases of solid iron (alpha, gamma, and delta) that vary based on temperature and pressure. A principal difference between solid phases

7830-421: The study of chemistry; some of them are: In chemistry, matter is defined as anything that has rest mass and volume (it takes up space) and is made up of particles . The particles that make up matter have rest mass as well – not all particles have rest mass, such as the photon . Matter can be a pure chemical substance or a mixture of substances. The atom is the basic unit of chemistry. It consists of

7920-633: The symmetry-allowed overlap of a p orbital on the boron atom with the in-phase combination of the three similarly oriented p orbitals on fluorine atoms. Others point to the ionic nature of the bonds in BF 3 . [REDACTED] BF 3 is manufactured by the reaction of boron oxides with hydrogen fluoride : Typically the HF is produced in situ from sulfuric acid and fluorite ( CaF 2 ). Approximately 2300-4500 tonnes of boron trifluoride are produced every year. For laboratory scale reactions, BF 3

8010-456: The π-donating blockage of the acidity. Boron trifluoride reacts with water to give boric acid and fluoroboric acid . The reaction commences with the formation of the aquo adduct, H 2 O−BF 3 , which then loses HF that gives fluoroboric acid with boron trifluoride. The heavier trihalides do not undergo analogous reactions, possibly due to the lower stability of the tetrahedral ions [BCl 4 ] and [BBr 4 ] . Because of

8100-532: Was the substance that neutralized the acid which supposedly destroyed the volatility or spirit of the acid and which imparted the property of solidity (i.e., gave a concrete base) to the resulting salt. Chemistry Chemistry is the scientific study of the properties and behavior of matter . It is a physical science within the natural sciences that studies the chemical elements that make up matter and compounds made of atoms , molecules and ions : their composition, structure, properties, behavior and

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