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136-398: 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 the changes they undergo during reactions with other substances . Chemistry also addresses

272-439: 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

408-538: A homogeneous system of linear equations , which are readily solved using mathematical methods. Such system always has the all-zeros trivial solution , which we are not interested in, but if there are any additional solutions, there will be infinite number of them. Any non-trivial solution will balance the chemical equation. A "preferred" solution is one with whole-number , mostly positive stoichiometric coefficients s j with greatest common divisor equal to one. Let us assign variables to stoichiometric coefficients of

544-412: A nucleus of protons and neutrons , and a surrounding "cloud" of orbiting electrons which "take up space". However, this is only somewhat correct because subatomic particles and their properties are governed by their quantum nature , which means they do not act as everyday objects appear to act – they can act like waves as well as particles , and they do not have well-defined sizes or positions. In

680-491: A quantity of matter . As such, there is no single universally agreed scientific meaning of the word "matter". Scientifically, the term "mass" is well-defined, but "matter" can be defined in several ways. Sometimes in the field of physics "matter" is simply equated with particles that exhibit rest mass (i.e., that cannot travel at the speed of light), such as quarks and leptons. However, in both physics and chemistry , matter exhibits both wave -like and particle -like properties,

816-476: A system of linear equations . Balanced equations are usually written with smallest natural-number coefficients. Yet sometimes it may be advantageous to accept a fractional coefficient, if it simplifies the other coefficients. The introductory example can thus be rewritten as In some circumstances the fractional coefficients are even inevitable. For example, the reaction corresponding to the standard enthalpy of formation must be written such that one molecule of

952-430: A baryon, is given a baryon number of 1/3. So the net amount of matter, as measured by the number of quarks (minus the number of antiquarks, which each have a baryon number of −1/3), which is proportional to baryon number, and number of leptons (minus antileptons), which is called the lepton number, is practically impossible to change in any process. Even in a nuclear bomb, none of the baryons (protons and neutrons of which

1088-635: A charge of −1  e . They also carry colour charge , which is the equivalent of the electric charge for the strong interaction . Quarks also undergo radioactive decay , meaning that they are subject to the weak interaction . Baryons are strongly interacting fermions, and so are subject to Fermi–Dirac statistics. Amongst the baryons are the protons and neutrons, which occur in atomic nuclei, but many other unstable baryons exist as well. The term baryon usually refers to triquarks—particles made of three quarks. Also, "exotic" baryons made of four quarks and one antiquark are known as pentaquarks , but their existence

1224-467: 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

1360-470: 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

1496-412: 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

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1632-623: A desired degree, the resulting substance is said to be chemically pure . Chemical substances can exist in several different physical states or phases (e.g. solids , liquids , gases , or plasma ) without changing their chemical composition. Substances transition between these phases of matter in response to changes in temperature or pressure . Some chemical substances can be combined or converted into new substances by means of chemical reactions . Chemicals that do not possess this ability are said to be inert . A definition of "matter" based on its physical and chemical structure is: matter

1768-535: 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

1904-441: A distance from other particles under everyday conditions; this creates the property of matter which appears to us as matter taking up space. For much of the history of the natural sciences , people have contemplated the exact nature of matter. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter , appeared in both ancient Greece and ancient India . Early philosophers who proposed

2040-443: A few of its theoretical properties. There is considerable speculation both in science and science fiction as to why the observable universe is apparently almost entirely matter (in the sense of quarks and leptons but not antiquarks or antileptons), and whether other places are almost entirely antimatter (antiquarks and antileptons) instead. In the early universe, it is thought that matter and antimatter were equally represented, and

2176-401: A list of reactants (the starting substances) on the left-hand side, an arrow symbol , and a list of products (substances formed in the chemical reaction) on the right-hand side. Each substance is specified by its chemical formula , optionally preceded by a number called stoichiometric coefficient . The coefficient specifies how many entities (e.g. molecules ) of that substance are involved in

2312-411: 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

2448-422: 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

2584-1155: A positive hydrogen ion to another substance in a chemical reaction; by extension, a base is the substance which receives that hydrogen ion. Matter In classical physics and general chemistry , matter is any substance that has mass and takes up space by having volume . All everyday objects that can be touched are ultimately composed of atoms , which are made up of interacting subatomic particles , and in everyday as well as scientific usage, matter generally includes atoms and anything made up of them, and any particles (or combination of particles ) that act as if they have both rest mass and volume . However it does not include massless particles such as photons , or other energy phenomena or waves such as light or heat . Matter exists in various states (also known as phases ). These include classical everyday phases such as solid , liquid , and gas – for example water exists as ice , liquid water, and gaseous steam – but other states are possible, including plasma , Bose–Einstein condensates , fermionic condensates , and quark–gluon plasma . Usually atoms can be imagined as

2720-405: 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

2856-516: A sea of degenerate electrons. At a microscopic level, the constituent "particles" of matter such as protons, neutrons, and electrons obey the laws of quantum mechanics and exhibit wave–particle duality. At an even deeper level, protons and neutrons are made up of quarks and the force fields ( gluons ) that bind them together, leading to the next definition. As seen in the above discussion, many early definitions of what can be called "ordinary matter" were based upon its structure or "building blocks". On

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2992-478: A single product is formed. This will often require that some reactant coefficients be fractional, as is the case with the formation of lithium fluoride : The method of inspection can be outlined as setting the most complex substance's stoichiometric coefficient to 1 and assigning values to other coefficients step by step such that both sides of the equation end up with the same number of atoms for each element. If any fractional coefficients arise during this process,

3128-447: A solid, (l) for a liquid, (g) for a gas, and (aq) for an aqueous solution . This is especially done when one wishes to emphasize the states or changes thereof. For example, the reaction of aqueous hydrochloric acid with solid (metallic) sodium to form aqueous sodium chloride and hydrogen gas would be written like this: That reaction would have different thermodynamic and kinetic properties if gaseous hydrogen chloride were to replace

3264-426: A subclass of matter. A common or traditional definition of matter is "anything that has mass and volume (occupies space )". For example, a car would be said to be made of matter, as it has mass and volume (occupies space). The observation that matter occupies space goes back to antiquity. However, an explanation for why matter occupies space is recent, and is argued to be a result of the phenomenon described in

3400-608: 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

3536-476: A temperature near absolute zero. The Pauli exclusion principle requires that only two fermions can occupy a quantum state, one spin-up and the other spin-down. Hence, at zero temperature, the fermions fill up sufficient levels to accommodate all the available fermions—and in the case of many fermions, the maximum kinetic energy (called the Fermi energy ) and the pressure of the gas becomes very large, and depends on

3672-414: 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

3808-409: 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

3944-586: 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

4080-421: 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,

4216-439: 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,

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4352-405: Is approximately 12.5  MeV/ c , which is low compared to the mass of a nucleon (approximately 938  MeV/ c ). The bottom line is that most of the mass of everyday objects comes from the interaction energy of its elementary components. The Standard Model groups matter particles into three generations, where each generation consists of two quarks and two leptons. The first generation

4488-461: 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

4624-523: 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

4760-470: 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

4896-464: 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

5032-631: Is expected to be color superconducting . Strange matter is hypothesized to occur in the core of neutron stars , or, more speculatively, as isolated droplets that may vary in size from femtometers ( strangelets ) to kilometers ( quark stars ). In particle physics and astrophysics , the term is used in two ways, one broader and the other more specific. Leptons are particles of spin- 1 ⁄ 2 , meaning that they are fermions . They carry an electric charge of −1  e (charged leptons) or 0  e (neutrinos). Unlike quarks, leptons do not carry colour charge , meaning that they do not experience

5168-464: 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,

5304-400: Is made up of atoms . Such atomic matter is also sometimes termed ordinary matter . As an example, deoxyribonucleic acid molecules (DNA) are matter under this definition because they are made of atoms. This definition can be extended to include charged atoms and molecules, so as to include plasmas (gases of ions) and electrolytes (ionic solutions), which are not obviously included in

5440-455: Is made up of neutron stars and white dwarfs. Strange matter is a particular form of quark matter , usually thought of as a liquid of up , down , and strange quarks. It is contrasted with nuclear matter , which is a liquid of neutrons and protons (which themselves are built out of up and down quarks), and with non-strange quark matter, which is a quark liquid that contains only up and down quarks. At high enough density, strange matter

5576-537: 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

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5712-485: Is more subtle than it first appears. All the particles that make up ordinary matter (leptons and quarks) are elementary fermions, while all the force carriers are elementary bosons. The W and Z bosons that mediate the weak force are not made of quarks or leptons, and so are not ordinary matter, even if they have mass. In other words, mass is not something that is exclusive to ordinary matter. The quark–lepton definition of ordinary matter, however, identifies not only

5848-436: Is natural to phrase the definition as: "ordinary matter is anything that is made of the same things that atoms and molecules are made of". (However, notice that one also can make from these building blocks matter that is not atoms or molecules.) Then, because electrons are leptons, and protons and neutrons are made of quarks, this definition in turn leads to the definition of matter as being "quarks and leptons", which are two of

5984-429: Is no such thing as "anti-mass" or negative mass , so far as is known, although scientists do discuss the concept. Antimatter has the same (i.e. positive) mass property as its normal matter counterpart. Different fields of science use the term matter in different, and sometimes incompatible, ways. Some of these ways are based on loose historical meanings from a time when there was no reason to distinguish mass from simply

6120-480: Is not a substance but rather a quantitative property of matter and other substances or systems; various types of mass are defined within physics – including but not limited to rest mass , inertial mass , relativistic mass , mass–energy . While there are different views on what should be considered matter, the mass of a substance has exact scientific definitions. Another difference is that matter has an "opposite" called antimatter , but mass has no opposite—there

6256-429: Is not generally accepted. Baryonic matter is the part of the universe that is made of baryons (including all atoms). This part of the universe does not include dark energy , dark matter , black holes or various forms of degenerate matter, such as those that compose white dwarf stars and neutron stars . Microwave light seen by Wilkinson Microwave Anisotropy Probe (WMAP) suggests that only about 4.6% of that part of

6392-403: Is the up and down quarks, the electron and the electron neutrino ; the second includes the charm and strange quarks, the muon and the muon neutrino ; the third generation consists of the top and bottom quarks and the tau and tau neutrino . The most natural explanation for this would be that quarks and leptons of higher generations are excited states of

6528-468: 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

6664-456: 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

6800-480: Is the full ionic equation from which the spectator ions have been removed. The net ionic equation of the proceeding reactions is: or, in reduced balanced form, In a neutralization or acid / base reaction, the net ionic equation will usually be: There are a few acid/base reactions that produce a precipitate in addition to the water molecule shown above. An example is the reaction of barium hydroxide with phosphoric acid , which produces not only water but also

6936-506: 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,

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7072-523: 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

7208-477: The Pauli exclusion principle , which applies to fermions . Two particular examples where the exclusion principle clearly relates matter to the occupation of space are white dwarf stars and neutron stars, discussed further below. Thus, matter can be defined as everything composed of elementary fermions. Although we do not encounter them in everyday life, antiquarks (such as the antiproton ) and antileptons (such as

7344-499: The Standard Model of particle physics , matter is not a fundamental concept because the elementary constituents of atoms are quantum entities which do not have an inherent "size" or " volume " in any everyday sense of the word. Due to the exclusion principle and other fundamental interactions , some " point particles " known as fermions ( quarks , leptons ), and many composites and atoms, are effectively forced to keep

7480-543: 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 the interconversion of conformers

7616-454: 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

7752-493: 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

7888-469: 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

8024-570: The energy–momentum tensor that quantifies the amount of matter. This tensor gives the rest mass for the entire system. Matter, therefore, is sometimes considered as anything that contributes to the energy–momentum of a system, that is, anything that is not purely gravity. This view is commonly held in fields that deal with general relativity such as cosmology . In this view, light and other massless particles and fields are all part of matter. In particle physics, fermions are particles that obey Fermi–Dirac statistics . Fermions can be elementary, like

8160-509: 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

8296-528: 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

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8432-645: The laws of nature . They coupled their ideas of soul, or lack thereof, into their theory of matter. The strongest developers and defenders of this theory were the Nyaya - Vaisheshika school, with the ideas of the Indian philosopher Kanada being the most followed. Buddhist philosophers also developed these ideas in late 1st-millennium CE, ideas that were similar to the Vaisheshika school, but ones that did not include any soul or conscience. Jain philosophers included

8568-556: The positron ) are the antiparticles of the quark and the lepton, are elementary fermions as well, and have essentially the same properties as quarks and leptons, including the applicability of the Pauli exclusion principle which can be said to prevent two particles from being in the same place at the same time (in the same state), i.e. makes each particle "take up space". This particular definition leads to matter being defined to include anything made of these antimatter particles as well as

8704-438: 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

8840-570: The soul ( jiva ), adding qualities such as taste, smell, touch, and color to each atom. They extended the ideas found in early literature of the Hindus and Buddhists by adding that atoms are either humid or dry, and this quality cements matter. They also proposed the possibility that atoms combine because of the attraction of opposites, and the soul attaches to these atoms, transforms with karma residue, and transmigrates with each rebirth . In ancient Greece , pre-Socratic philosophers speculated

8976-551: The strong interaction . Leptons also undergo radioactive decay, meaning that they are subject to the weak interaction . Leptons are massive particles, therefore are subject to gravity. In bulk , matter can exist in several different forms, or states of aggregation, known as phases , depending on ambient pressure , temperature and volume . A phase is a form of matter that has a relatively uniform chemical composition and physical properties (such as density , specific heat , refractive index , and so forth). These phases include

9112-515: 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

9248-410: The annihilation. In short, matter, as defined in physics, refers to baryons and leptons. The amount of matter is defined in terms of baryon and lepton number. Baryons and leptons can be created, but their creation is accompanied by antibaryons or antileptons; and they can be destroyed by annihilating them with antibaryons or antileptons. Since antibaryons/antileptons have negative baryon/lepton numbers,

9384-478: The antiparticle partners of one another. In October 2017, scientists reported further evidence that matter and antimatter , equally produced at the Big Bang , are identical, should completely annihilate each other and, as a result, the universe should not exist. This implies that there must be something, as yet unknown to scientists, that either stopped the complete mutual destruction of matter and antimatter in

9520-419: The arrow. Both extensions are used in the example illustration of a mechanism. Use of negative stoichiometric coefficients at either side of the equation (like in the example below) is not widely adopted and is often discouraged. Because no nuclear reactions take place in a chemical reaction, the chemical elements pass through the reaction unchanged. Thus, each side of the chemical equation must represent

9656-410: The arrow. If no specific acid or base is required, another way of denoting the use of an acidic or basic medium is to write H or OH (or even "acid" or "base") on top of the arrow. Specific conditions of the temperature and pressure, as well as the presence of catalysts, may be indicated in the same way. The standard notation for chemical equations only permits all reactants on one side, all products on

9792-490: 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

9928-455: The atomic nuclei are composed) are destroyed—there are as many baryons after as before the reaction, so none of these matter particles are actually destroyed and none are even converted to non-matter particles (like photons of light or radiation). Instead, nuclear (and perhaps chromodynamic) binding energy is released, as these baryons become bound into mid-size nuclei having less energy (and, equivalently , less mass) per nucleon compared to

10064-650: The atoms definition. Alternatively, one can adopt the protons, neutrons, and electrons definition. A definition of "matter" more fine-scale than the atoms and molecules definition is: matter is made up of what atoms and molecules are made of , meaning anything made of positively charged protons , neutral neutrons , and negatively charged electrons . This definition goes beyond atoms and molecules, however, to include substances made from these building blocks that are not simply atoms or molecules, for example electron beams in an old cathode ray tube television, or white dwarf matter—typically, carbon and oxygen nuclei in

10200-521: The basic element is fire, though perhaps he means that all is change. Empedocles (c. 490–430 BCE) spoke of four elements of which everything was made: earth, water, air, and fire. Meanwhile, Parmenides argued that change does not exist, and Democritus argued that everything is composed of minuscule, inert bodies of all shapes called atoms, a philosophy called atomism . All of these notions had deep philosophical problems. Chemical equation A chemical equation (see an example below) consists of

10336-638: The chemical equation from the previous section and write the corresponding linear equations: C: s 1 = s 3 H: 4 s 1 = 2 s 4 O: 2 s 2 = 2 s 3 + s 4 {\displaystyle \quad \;\;\;{\begin{aligned}{\text{C:}}&&s_{1}&=s_{3}\\{\text{H:}}&&4s_{1}&=2s_{4}\\{\text{O:}}&&2s_{2}&=2s_{3}+s_{4}\end{aligned}}} All solutions to this system of linear equations are of

10472-435: The chemical formulas are read using IUPAC nomenclature , which could verbalise this equation as "two hydrochloric acid molecules and two sodium atoms react to form two formula units of sodium chloride and a hydrogen gas molecule." Different variants of the arrow symbol are used to denote the type of a reaction: To indicate physical state of a chemical, a symbol in parentheses may be appended to its formula: (s) for

10608-412: 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

10744-414: The difference between the rest mass of the products of the annihilation and the rest mass of the original particle–antiparticle pair, which is often quite large. Depending on which definition of "matter" is adopted, antimatter can be said to be a particular subclass of matter, or the opposite of matter. Antimatter is not found naturally on Earth, except very briefly and in vanishingly small quantities (as

10880-691: The disappearance of antimatter requires an asymmetry in physical laws called CP (charge–parity) symmetry violation , which can be obtained from the Standard Model, but at this time the apparent asymmetry of matter and antimatter in the visible universe is one of the great unsolved problems in physics . Possible processes by which it came about are explored in more detail under baryogenesis . Formally, antimatter particles can be defined by their negative baryon number or lepton number , while "normal" (non-antimatter) matter particles have positive baryon or lepton number. These two classes of particles are

11016-399: The early forming universe, or that gave rise to an imbalance between the two forms. Two quantities that can define an amount of matter in the quark–lepton sense (and antimatter in an antiquark–antilepton sense), baryon number and lepton number , are conserved in the Standard Model. A baryon such as the proton or neutron has a baryon number of one, and a quark, because there are three in

11152-414: The early phase of the universe and still floating about. In cosmology , dark energy is the name given to the source of the repelling influence that is accelerating the rate of expansion of the universe . Its precise nature is currently a mystery, although its effects can reasonably be modeled by assigning matter-like properties such as energy density and pressure to the vacuum itself. Fully 70% of

11288-448: The early universe and the Big Bang theory require that this matter have energy and mass, but not be composed of ordinary baryons (protons and neutrons). The commonly accepted view is that most of the dark matter is non-baryonic in nature . As such, it is composed of particles as yet unobserved in the laboratory. Perhaps they are supersymmetric particles , which are not Standard Model particles but relics formed at very high energies in

11424-428: The electron—or composite, like the proton and neutron. In the Standard Model , there are two types of elementary fermions: quarks and leptons, which are discussed next. Quarks are massive particles of spin- 1 ⁄ 2 , implying that they are fermions . They carry an electric charge of − 1 ⁄ 3   e (down-type quarks) or + 2 ⁄ 3   e (up-type quarks). For comparison, an electron has

11560-438: The elementary building blocks of matter, but also includes composites made from the constituents (atoms and molecules, for example). Such composites contain an interaction energy that holds the constituents together, and may constitute the bulk of the mass of the composite. As an example, to a great extent, the mass of an atom is simply the sum of the masses of its constituent protons, neutrons and electrons. However, digging deeper,

11696-429: 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 ,

11832-518: The field of thermodynamics . In nanomaterials, the vastly increased ratio of surface area to volume results in matter that can exhibit properties entirely different from those of bulk material, and not well described by any bulk phase (see nanomaterials for more details). Phases are sometimes called states of matter , but this term can lead to confusion with thermodynamic states . For example, two gases maintained at different pressures are in different thermodynamic states (different pressures), but in

11968-447: The first generations. If this turns out to be the case, it would imply that quarks and leptons are composite particles , rather than elementary particles . This quark–lepton definition of matter also leads to what can be described as "conservation of (net) matter" laws—discussed later below. Alternatively, one could return to the mass–volume–space concept of matter, leading to the next definition, in which antimatter becomes included as

12104-450: The following form, where r is any real number : The choice of r = 1 yields the preferred solution, which corresponds to the balanced chemical equation: The system of linear equations introduced in the previous section can also be written using an efficient matrix formalism. First, to unify the reactant and product stoichiometric coefficients s j , let us introduce the quantity called stoichiometric number , which simplifies

12240-399: The following form, where r is any real number: The choice of r = 1 and a sign -flip of the first two rows yields the preferred solution to the balancing problem: An ionic equation is a chemical equation in which electrolytes are written as dissociated ions . Ionic equations are used for single and double displacement reactions that occur in aqueous solutions . For example, in

12376-516: The following precipitation reaction: the full ionic equation is: or, with all physical states included: In this reaction, the Ca and the NO 3 ions remain in solution and are not part of the reaction. That is, these ions are identical on both the reactant and product side of the chemical equation. Because such ions do not participate in the reaction, they are called spectator ions . A net ionic equation

12512-710: 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

12648-444: 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

12784-470: The four types of elementary fermions (the other two being antiquarks and antileptons, which can be considered antimatter as described later). Carithers and Grannis state: "Ordinary matter is composed entirely of first-generation particles, namely the [up] and [down] quarks, plus the electron and its neutrino." (Higher generations particles quickly decay into first-generation particles, and thus are not commonly encountered. ) This definition of ordinary matter

12920-408: The fractions of energy in the universe contributed by different sources. Ordinary matter is divided into luminous matter (the stars and luminous gases and 0.005% radiation) and nonluminous matter (intergalactic gas and about 0.1% neutrinos and 0.04% supermassive black holes). Ordinary matter is uncommon. Modeled after Ostriker and Steinhardt. For more information, see NASA . Ordinary matter, in

13056-408: The hydrochloric acid as a reactant: Alternately, an arrow without parentheses is used in some cases to indicate formation of a gas ↑ or precipitate ↓. This is especially useful if only one such species is formed. Here is an example indicating that hydrogen gas is formed: If the reaction requires energy, it is indicated above the arrow. A capital Greek letter delta (Δ) or a triangle (△) is put on

13192-443: 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:

13328-452: The linear equations to where J is the total number of reactant and product substances (formulas) in the chemical equation. Placement of the values a ij at row i and column j of the composition matrix and arrangement of the stoichiometric numbers into the stoichiometric vector allows the system of equations to be expressed as a single matrix equation : Like previously, any nonzero stoichiometric vector ν , which solves

13464-472: 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

13600-414: The mass–energy density of the universe. Hadronic matter can refer to 'ordinary' baryonic matter, made from hadrons (baryons and mesons ), or quark matter (a generalisation of atomic nuclei), i.e. the 'low' temperature QCD matter . It includes degenerate matter and the result of high energy heavy nuclei collisions. In physics, degenerate matter refers to the ground state of a gas of fermions at

13736-403: The matrix equation, will balance the chemical equation. The set of solutions to the matrix equation is a linear space called the kernel of the matrix A . For this space to contain nonzero vectors ν , i.e. to have a positive dimension J N , the columns of the composition matrix A must not be linearly independent . The problem of balancing a chemical equation then becomes

13872-545: The matter density in the universe appears to be in the form of dark energy. Twenty-six percent is dark matter. Only 4% is ordinary matter. So less than 1 part in 20 is made out of matter we have observed experimentally or described in the standard model of particle physics. Of the other 96%, apart from the properties just mentioned, we know absolutely nothing. Exotic matter is a concept of particle physics , which may include dark matter and dark energy but goes further to include any hypothetical material that violates one or more of

14008-401: 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 a fundamental level. For example, chemistry explains aspects of plant growth ( botany ),

14144-412: The number of fermions rather than the temperature, unlike normal states of matter. Degenerate matter is thought to occur during the evolution of heavy stars. The demonstration by Subrahmanyan Chandrasekhar that white dwarf stars have a maximum allowed mass because of the exclusion principle caused a revolution in the theory of star evolution. Degenerate matter includes the part of the universe that

14280-414: The ordinary quark and lepton, and thus also anything made of mesons , which are unstable particles made up of a quark and an antiquark. In the context of relativity , mass is not an additive quantity, in the sense that one cannot add the rest masses of particles in a system to get the total rest mass of the system. In relativity, usually a more general view is that it is not the sum of rest masses , but

14416-401: The original small (hydrogen) and large (plutonium etc.) nuclei. Even in electron–positron annihilation , there is no net matter being destroyed, because there was zero net matter (zero total lepton number and baryon number) to begin with before the annihilation—one lepton minus one antilepton equals zero net lepton number—and this net amount matter does not change as it simply remains zero after

14552-419: 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

14688-477: The other, and all stoichiometric coefficients positive. For example, the usual form of the equation for dehydration of methanol to dimethylether is: Sometimes an extension is used, where some substances with their stoichiometric coefficients are moved above or below the arrow, preceded by a plus sign or nothing for a reactant, and by a minus sign for a product. Then the same equation can look like this: Such notation serves to hide less important substances from

14824-447: The overall baryon/lepton numbers are not changed, so matter is conserved. However, baryons/leptons and antibaryons/antileptons all have positive mass, so the total amount of mass is not conserved. Further, outside of natural or artificial nuclear reactions, there is almost no antimatter generally available in the universe (see baryon asymmetry and leptogenesis ), so particle annihilation is rare in normal circumstances. Pie chart showing

14960-408: The particulate theory of matter include the ancient Indian philosopher Kanada (c. 6th–century BCE or after), pre-Socratic Greek philosopher Leucippus (~490 BCE), and pre-Socratic Greek philosopher Democritus (~470–380 BCE). Matter should not be confused with mass, as the two are not the same in modern physics. Matter is a general term describing any 'physical substance'. By contrast, mass

15096-414: The presence of fractions may be eliminated (at any time) by multiplying all coefficients by their lowest common denominator . Balancing of the chemical equation for the complete combustion of methane is achieved as follows: For each chemical element (or nuclide or unchanged moiety or charge) i , its conservation requirement can be expressed by the mathematical equation where This results in

15232-400: The problem of determining the J N -dimensional kernel of the composition matrix. It is important to note that only for J N  = 1 will there be a unique preferred solution to the balancing problem. For J N  > 1 there will be an infinite number of preferred solutions with J N of them linearly independent. If J N  = 0, there will be only

15368-472: The properties of known forms of matter. Some such materials might possess hypothetical properties like negative mass . In ancient India , the Buddhist , Hindu , and Jain philosophical traditions each posited that matter was made of atoms ( paramanu , pudgala ) that were "eternal, indestructible, without parts, and innumerable" and which associated or dissociated to form more complex matter according to

15504-399: The protons and neutrons are made up of quarks bound together by gluon fields (see dynamics of quantum chromodynamics ) and these gluon fields contribute significantly to the mass of hadrons. In other words, most of what composes the "mass" of ordinary matter is due to the binding energy of quarks within protons and neutrons. For example, the sum of the mass of the three quarks in a nucleon

15640-503: The quarks and leptons definition, constitutes about 4% of the energy of the observable universe . The remaining energy is theorized to be due to exotic forms, of which 23% is dark matter and 73% is dark energy . In astrophysics and cosmology , dark matter is matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter. Observational evidence of

15776-627: 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

15912-478: 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

16048-427: The reaction arrow to show that energy in the form of heat is added to the reaction. The expression hν is used as a symbol for the addition of energy in the form of light. Other symbols are used for other specific types of energy or radiation. Similarly, if a reaction requires a certain medium with certain specific characteristics, then the name of the acid or base that is used as a medium may be placed on top of

16184-433: 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 ,

16320-491: The reaction on a molecular basis. If not written explicitly, the coefficient is equal to 1. Multiple substances on any side of the equation are separated from each other by a plus sign . As an example, the equation for the reaction of hydrochloric acid with sodium can be denoted: Given the formulas are fairly simple, this equation could be read as "two H-C-L plus two N-A yields two N-A-C-L and H two." Alternately, and in general for equations involving complex chemicals,

16456-408: The result of radioactive decay , lightning or cosmic rays ). This is because antimatter that came to exist on Earth outside the confines of a suitable physics laboratory would almost instantly meet the ordinary matter that Earth is made of, and be annihilated. Antiparticles and some stable antimatter (such as antihydrogen ) can be made in tiny amounts, but not in enough quantity to do more than test

16592-544: 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

16728-403: 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

16864-555: The same phase (both are gases). Antimatter is matter that is composed of the antiparticles of those that constitute ordinary matter. If a particle and its antiparticle come into contact with each other, the two annihilate ; that is, they may both be converted into other particles with equal energy in accordance with Albert Einstein 's equation E = mc . These new particles may be high-energy photons ( gamma rays ) or other particle–antiparticle pairs. The resulting particles are endowed with an amount of kinetic energy equal to

17000-473: 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

17136-486: The same number of atoms of any particular element (or nuclide , if different isotopes are taken into account). The same holds for the total electric charge , as stated by the charge conservation law. An equation adhering to these requirements is said to be balanced . A chemical equation is balanced by assigning suitable values to the stoichiometric coefficients. Simple equations can be balanced by inspection, that is, by trial and error. Another technique involves solving

17272-574: The scale of elementary particles, a definition that follows this tradition can be stated as: "ordinary matter is everything that is composed of quarks and leptons ", or "ordinary matter is everything that is composed of any elementary fermions except antiquarks and antileptons". The connection between these formulations follows. Leptons (the most famous being the electron ), and quarks (of which baryons , such as protons and neutrons , are made) combine to form atoms , which in turn form molecules . Because atoms and molecules are said to be matter, it

17408-458: The sides of the equation, to make the type of reaction at hand more obvious, and to facilitate chaining of chemical equations. This is very useful in illustrating multi-step reaction mechanisms . Note that the substances above or below the arrows are not catalysts in this case, because they are consumed or produced in the reaction like ordinary reactants or products. Another extension used in reaction mechanisms moves some substances to branches of

17544-421: The so-called wave–particle duality . A chemical substance is a unique form of matter with constant chemical composition and characteristic properties . Chemical substances may take the form of a single element or chemical compounds . If two or more chemical substances can be combined without reacting , they may form a chemical mixture . If a mixture is separated to isolate one chemical substance to

17680-645: 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

17816-695: 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

17952-419: 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

18088-445: The three familiar ones ( solids , liquids , and gases ), as well as more exotic states of matter (such as plasmas , superfluids , supersolids , Bose–Einstein condensates , ...). A fluid may be a liquid, gas or plasma. There are also paramagnetic and ferromagnetic phases of magnetic materials . As conditions change, matter may change from one phase into another. These phenomena are called phase transitions and are studied in

18224-472: The underlying nature of the visible world. Thales (c. 624 BCE–c. 546 BCE) regarded water as the fundamental material of the world. Anaximander (c. 610 BCE–c. 546 BCE) posited that the basic material was wholly characterless or limitless: the Infinite ( apeiron ). Anaximenes (flourished 585 BCE, d. 528 BCE) posited that the basic stuff was pneuma or air. Heraclitus (c. 535 BCE–c. 475 BCE) seems to say

18360-411: The universe within range of the best telescopes (that is, matter that may be visible because light could reach us from it) is made of baryonic matter. About 26.8% is dark matter, and about 68.3% is dark energy. The great majority of ordinary matter in the universe is unseen, since visible stars and gas inside galaxies and clusters account for less than 10 per cent of the ordinary matter contribution to

18496-422: The unusable trivial solution, the zero vector. Techniques have been developed to quickly calculate a set of J N independent solutions to the balancing problem, which are superior to the inspection and algebraic method in that they are determinative and yield all solutions to the balancing problem. Using the same chemical equation again, write the corresponding matrix equation: Its solutions are of

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