# Glossary of chemistry terms

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This glossary of chemistry terms is a list of terms and definitions relevant to chemistry, including chemical laws, diagrams and formulae, laboratory tools, glassware, and equipment. Chemistry is a physical science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions; it has an extensive vocabulary and a significant amount of jargon.

Note: All periodic table references refer to the IUPAC Style of the Periodic Table.

## A

absolute zero
A theoretical condition concerning a system at zero kelvin, where a system does not emit or absorb energy (all atoms are at rest).
absorbance
abundance
accuracy
How close a measured value is to the actual or true value. Compare precision.
acid
A compound that, when dissolved in water, gives a pH of less than 7.0 or a compound that donates a hydrogen ion.
acid anhydride
a compound with two acyl groups bound to a single oxygen atom
acid dissociation constant
A quantitative measure of the strength of an acid in solution expressed as an equilibrium constant for a chemical dissociation reaction in the context of acid-base reactions. It is generally denoted by the symbol Ka. Also called acid ionization constant or acidity constant.
actinides
The periodic series of metallic elements with atomic numbers 89 to 103, from actinium through lawrencium. Also called actinoids.
activated complex
A structure that forms because of a collision between molecules while new bonds are formed.
activation energy
The minimum energy which must be available to a chemical system with potential reactants in order to result in a chemical reaction.
activity series
actual yield
acyclic
Containing only linear structures of atoms (particularly in hydrocarbons).
In organic chemistry, when two or more molecules combine to make a larger one.
The tendency of dissimilar particles or surfaces to cling to one another as a result of intermolecular forces. Compare cohesion.
aeration
The mixing of air into a liquid or a solid.
alcohol
Any organic compound consisting of a hydroxyl functional group attached to a saturated carbon atom.
aldehyde
Any organic compound consisting of a carbonyl group attached to a hydrogen atom and any other R-group.
alkali metal
Any of the metallic elements belonging to Group 1 of the periodic table: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr).
alkaline earth metal
Any of the metallic elements belonging to Group 2 of the periodic table: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
alkane
Any saturated acyclic hydrocarbon.
alkene
An unsaturated hydrocarbon containing at least one pair of double-bonded carbons.
alkyl group
A functional group consisting of an alkane missing a hydrogen atom.
alkyne
An unsaturated hydrocarbon containing at least one pair of triple-bonded carbons.
allomer
A substance that differs in chemical composition but has the same crystalline structure as another substance.
allotrope
Elements that can have different structures (and therefore different forms), such as carbon (diamonds, graphite, and fullerene).
alloy
A mixture of metals or of a metal and another element which in combination exhibit a metallic bonding character. Common examples include bronze, brass, and pewter.
amalgam
amplitude
The maximum distance that the particles of the medium carrying the wave move away from their rest position.
anion
A negatively charged ion.
anode
1) An electrode through which the conventional electric current (the flow of positive charges) enters into a polarized electrical circuit; 2) the wire or plate of an electrochemical cell having an excess positive charge. Negatively charged anions always move toward the anode. Compare cathode.
aqueous solution
A solution in which the solvent is water. It is denoted in chemical equations by appending (aq) to a chemical formula.
aromaticity
A chemical property of conjugated rings of atoms, such as benzene, which results in unusually high stability.
atom
A chemical element in its smallest form, made up of protons and neutrons within the nucleus and electrons circling the nucleus.
An atom with protons, neutrons, and electrons labelled
atomic mass
The mass of an atom, typically expressed in unified atomic mass units and nearly equivalent to the mass number.
atomic mass unit
See unified atomic mass unit.
atomic number
The number of protons found in the nucleus of an atom of a given chemical element. It is identical to the charge number of the nucleus and is used in the periodic table to uniquely identify each chemical element. Also called the proton number.
atomic orbital
the region where the electron of the atom may be found
atomic weight
average atomic mass
The number of particles in one mole of a substance (6.02×1023).
azeotrope
A mixture of liquids whose composition is unchanged by distillation.

## B

barometer
A device used to measure atmospheric pressure.
base
A substance that accepts a proton and has a high pH; a common example is sodium hydroxide (NaOH).
base anhydride
Oxides of group I and II metal elements.
beaker
Beer–Lambert law
biochemistry
The study of the chemistry of biological systems and organisms.
Bohr model
boiling
See vaporization.
boiling point
The temperature at which a liquid substance starts to boil.
boiling-point elevation
the process where the boiling point is elevated by adding a substance
bond
The attraction and repulsion between atoms and molecules that is a cornerstone of chemistry.
Boyle's law
for a given mass of gas at constant temperature, the volume varies inversely with the pressure
Bragg's law
Brønsted–Lowry acid
Any chemical species that readily donates a proton.
Brønsted–Lowry acid–base reaction
Brønsted–Lowry base
Any chemical species that readily accepts a proton.
buckminsterfullerene
buffered solution
An aqueous solution consisting of a weak acid and its conjugate base or a weak base and its conjugate acid that resists changes in pH when strong acids or bases are added.
bumping
bung
burette
Glassware used to dispense specific amounts of liquid when precision is necessary (e.g. titration and resource-dependent reactions). Also called a buret.

## C

calorimeter
A device used to measure heat.
catalyst
Any element or compound that facilitates an increase in the speed of a chemical reaction but which is not consumed or destroyed during the reaction. It is considered both a reactant and a product of the reaction.
cathode
An electrode from which the conventional electric current (the flow of positive charges) exits a polarized electrical circuit. Positively charged cations always move toward the cathode, though the cathode's polarity can be positive or negative depending on the type of electrical device and how it is being operated. Compare anode.
cation
A positively charged ion.
centrifugation
centrifuge
equipment used to separate substances based on density by rotating the tubes around a centred axis
cell potential
the force in a galvanic cell that pulls electron through reducing agent to oxidizing agent
chain reaction
charge number
A quantized value of electric charge calculated as the electric charge in coulombs divided by the elementary-charge constant, or z = q/e. Charge numbers for ions are denoted in superscript (e.g. Na+ indicates a sodium ion with a charge number of positive one). Atomic numbers are charge numbers of atomic nuclei.
Charles's law
When the pressure on a sample of a dry gas is held constant, the Kelvin temperature is directly proportional to its volume.
chelation
A type of bonding involving the formation of two separate coordinate covalent bonds between a polydentate ligand and a single central metal ion. The ligand is usually an organic compound called a chelant or chelating agent.
chemical composition
The identity and relative number of the elements that make up a chemical compound, which can often be expressed with a chemical formula.
chemical formula
Any of various means of concisely displaying information about the chemical composition of a compound or molecule using letters, numbers, and/or typographical symbols. Chemical formulas, such as empirical and molecular formulas, can only indicate the identities and numerical proportions of the atoms in a compound and are therefore more limited in descriptive power than chemical names and structural formulas.
chemical law
A law of nature relevant to chemistry, such as the law of conservation of mass.
chemical nomenclature
chemical process
chemical reaction
The change of one or more substances into another or multiple substances.
chemical species
chemical substance
A form of matter that has constant chemical composition and characteristic properties and which cannot be separated into simpler components by purely physical methods (i.e. without breaking chemical bonds). It is often called a pure substance to distinguish it from a mixture.
chemistry
The scientific discipline that studies chemical substances, compounds, and molecules composed of atoms of various chemical elements, as well as their composition, structure, properties, behavior, and the changes they undergo during reactions with other substances.
chirality
cis–trans isomerism
closed system
cohesion
The tendency of similar particles or surfaces to cling to one another as a result of intermolecular forces. Compare adhesion.
colligative property
A property of solutions that depends upon the ratio of the number of solute particles to the number of solvent particles in the solution, and not on the nature of the chemical species present.
colloid
A mixture of evenly dispersed substances, such as many milks.
combustion
An exothermic reaction between an oxidant and a fuel that produces large amounts of heat and often light.
An example of combustion
Commission on Isotopic Abundances and Atomic Weights (CIAAW)
compression
An area in a longitudinal wave where the particles are closer and pushed in.
compound
A substance that is made up of two or more chemically bonded elements.
concentration
condensation
The phase transition of a substance from a gas to a liquid.
condosity
A comparative measurement of the electrical conductivity of a solution, defined as the molar concentration of a sodium chloride (NaCl) solution that has the same specific electrical conductance as the solution under test and expressed in units of moles per unit volume.
conductor
Any object or material that allows the flow of an electric current in one or more directions. Compare insulator.
conformation
The spatial arrangement of atoms affording distinction between stereoisomers which can be interconverted by rotations about formally single bonds.
conjugate acid
conjugate base
conjugated system
cooling curve
coordinate chemistry
coordinate covalent bond
coordination complex
corrosion
An irreversible interfacial chemical reaction of a material with its environment which results in consumption of the material or dissolution into the material of an external component of the environment.
coulomb
The SI unit of electric charge (symbol: C), defined as the charge transported by a constant current of one ampere in one second.
covalent bond
A chemical bond that involves the sharing of electron pairs between atoms. The stable balance of attractive and repulsive forces that occurs between atoms when they share electrons is known as covalent bonding. A covalent bond is also called a molecular bond.
The diatomic hydrogen molecule, H2 (right), is formed by a covalent bond when two single hydrogen atoms share two electrons
crest
The highest point in a wave.
critical mass
critical point
crystal
A solid whose constituent particles (such as atoms, ions, or molecules) are arranged in an orderly periodic microscopic structure, forming a lattice that extends in all directions.
crystallography
cuvette
A type of glassware used in spectroscopic experiments. It is usually made of plastic, glass or quartz and should be as clean and clear as possible.
cyclotron

## D

d-block
Dalton's law of partial pressures
deionization
The removal of ions, and in water's case, mineral ions such as sodium, iron and calcium.
deliquescence
Substances that absorb water from the atmosphere to form liquid solutions.
delocalized electron
density
An intensive property of a substance defined as mass per unit volume or d = m/V.
denticity
The number of donor groups in a single ligand that bind to a central atom in a coordination complex.
dependent variable
deposition
The settling of particles within a solution or mixture.
diatomic
Composed of two atoms.
diatomic molecule
Any molecule composed of only two atoms, of the same or different elements.
diffusion
dimer
dipolar bond
dipole
The electric or magnetic separation of charge.
dipole moment
The polarity of a polar covalent bond.
dispersion
dissociation
dissolution
The interaction of a solvent with the molecules or ions of a solute, involving bond formation, hydrogen bonding, and van der Waals forces. Also called solvation.
A sodium ion (Na+) forms a solvation complex with water molecules when dissolved in an aqueous solution
distillation
double bond
A chemical bond involving the covalent sharing of two pairs of electrons.
double-replacement reaction
ductility
A measure of a material's ability to undergo significant plastic deformation before rupturing, typically expressed as percent elongation or percent area reduction from a tensile test and popularly characterized by the material's ability to be stretched into a wire. Also called malleability.

## E

earth metal
See alkaline earth metal.
electrolyte
A solution that conducts a certain amount of electric current and can be split categorically into weak and strong electrolytes.
electrochemical cell
Using a chemical reaction's current, electromotive force is made.
A type of wave that can go through vacuums as well as material and is classified as a self-propagating wave.
electromagnetic spectrum
electromagnetism
Fields with an electric charge and electrical properties that change the way that particles move and interact.
electromotive force
A device that gains energy as electric charges pass through it.
electron
A subatomic particle with a net charge that is negative.
electron configuration
electron pair
Two electrons which occupy the same molecular orbital but have opposite spins. Electron pairs form chemical bonds or occur as lone pairs of valence electrons; it is also possible for electrons to occur as unpaired electrons.
electron shell
An orbital around an atom's nucleus containing a fixed number of electrons (usually two or eight).
electronegativity
electric charge
A measured property (coulombs) that determines electromagnetic interaction.
element
A species of atoms having the same number of protons in their atomic nuclei and hence the same atomic number. Chemical elements constitute all of the ordinary matter in the universe; 118 elements have been identified and are organized by their various chemical properties in the periodic table of the elements.
enantiomer
enantiomorph
endothermic process
energy
A system's ability to do work.
enthalpy
A measure of the total energy of a thermodynamic system. Usually symbolized as H.
enthalpy of fusion
entropy
The amount of energy not available for work in a closed thermodynamic system. Usually symbolized as S.
environmental chemistry
enzyme
A protein catalyst that speeds up a chemical reaction.
empirical formula
Also called the simplest formula, gives the simplest whole-number ratio of atoms of each element present in a compound.
equilibrium
Universally, it is the condition of a system in which all competing influences are balanced. Chemical equilibrium is the state in which the concentrations of the reactants and products have stopped changing in time.
Eppendorf tube
A generalized and trademarked name used for a microcentrifuge tube.
exothermic process
extensive property
extraction
extrinsic property

## F

f-block
freezing
The phase transition of a substance from a liquid to a solid.
A unit of electric charge widely used in electrochemistry and equal to ~ 96,500 coulombs. It represents 1 mol of electrons, or the Avogadro number of electrons: 6.022 × 1023 electrons. F = 96 485.339 9(24) C/mol.
A two-part law that Michael Faraday published about electrolysis. The mass of a substance altered at an electrode during electrolysis is directly proportional to the quantity of electricity transferred at that electrode; the mass of an elemental material altered at an electrode is directly proportional to the element's equivalent weight.
Fick's laws of diffusion
filtrate
first-order reaction
formal charge
fractional distillation
freezing-point depression
frequency
A measurement of the number of cycles of a given process per unit of time. The SI unit for measuring frequency is the hertz (Hz), with 1 Hz = 1 cycle per second.
functional group

## G

galvanic cell
A type of battery made up of electrochemicals with two different metals connected by a salt bridge.
gas
One of the four fundamental states of matter, characterized by high-energy particles which fill their container but have no definite shape or volume.
gas chromatography
Gay-Lussac's law
A chemical law used for each of the two relationships derived by French chemist Joseph Louis Gay-Lussac and which concern the properties of gases, though the name is more usually applied to his law of combining volumes.
geochemistry
The study of the chemistry and chemical composition of the Earth and geological processes.
Gibbs energy
A value that indicates the spontaneity of a reaction. Usually symbolized as G.
glass
gram-atom
One gram-atom of an element is defined as a collection of 6.023X10^23 atoms.
Grignard reaction
ground glass joint
An apparatus designed to quickly and easily fit two pieces of leak-tight glassware together, featuring ground glass surfaces and typically a custom-made conical taper.
group
A column of the periodic table of the elements and the elements that share it. Also called a family. Compare period.

## H

halogen
Any of the five non-metallic elements of Group 17 of the periodic table: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
A subatomic particle of a type including the baryons and mesons that can take part in the strong interaction.
heat
Energy transferred from one system to another by thermal interaction.
heat of fusion
See enthalpy of fusion.
Henry's law
Hess's law
Hund's rules
hydrate
hydration reaction
hydrogen
hydrogen bond
A form of electrostatic interaction between an electronegative atom and a hydrogen atom bound to a second electronegative atom. Hydrogen bonding is unique because the small size of the hydrogen atoms permits proximity of the interacting electrical charges, and may occur as an intermolecular or intramolecular force.
hydrogenation
hydrolysis
The cleavage of a chemical bond by the addition of water.

## I

ideal gas
ideal gas constant
The proportionality constant in the ideal gas law, defined as 0.08206 L·atm/(K·mol). Also called the universal gas constant.
ideal gas law
the volume of a gas is proportional to the amount of gas and its Kelvin temperature and inversely proportional to its pressure
independent variable
indicator
A special compound added to a solution that changes color depending on the acidity of the solution; different indicators have different colors and effective pH ranges.
radioactivity caused by bombarding a stable isotope with elemental particles, forming a radioactive isotope
inorganic compound
Any chemical compound that does not contain carbon, though there are exceptions.
inorganic chemistry
A branch of chemistry concerning the chemical properties and reactions of inorganic compounds.
insulator
Any material that resists the flow of electric current. Compare conductor.
intensive property
intermediate
intermolecular force
International System of Units (SI)
International Union of Pure and Applied Chemistry (IUPAC)
An international federation of chemists that is recognized as the world authority in developing standards for chemical nomenclature and other methodologies in chemistry.
intramolecular force
intrinsic property
ion
A molecule that has gained or lost one or more electrons from its neutral state and therefore possesses a negative or positive electric charge.
ionic bond
An electrostatic attraction between oppositely charged ions.
An ionic bond between a sodium atom (Na) and a fluorine atom (F). The sodium atom loses its sole valence electron (leaving the atom with a positive electrical charge), and the fluorine atom gains this same electron via an exothermic process (giving the atom a negative electrical charge). The oppositely charged ions are then attracted to each other to form a new compound called sodium fluoride.
ionization
The breaking up of a chemical compound into separate ions.
isoelectronic
isomer
isomerization
isotope
A variant of a particular chemical element which differs in the number of neutrons present in the nucleus. All isotopes of a given element have the same number of protons in each atom.

## J

joule
The SI unit of energy (symbol: J); 1 joule = 1 Newton-meter.

## K

kelvin
The SI base unit of temperature (symbol: K). The Kelvin scale is an absolute thermodynamic temperature scale that uses absolute zero as its null point.
ketone
An organic compound with a carbonyl group between two carbon atoms.
kinetics
A subfield of chemistry specializing in reaction rates.
kinetic energy
The energy of an object due to its motion.

## L

lanthanides
The periodic series of metallic elements with atomic numbers 57 through 71, from lanthanum through lutetium. Also called lanthanoids.
lattice
The unique arrangement of atoms or molecules in a crystalline liquid or solid.
lattice energy
law of conservation of energy
law of conservation of mass
law of multiple proportions
laws of thermodynamics
leveling effect
Lewis acid
Lewis base
Lewis structure
ligand
light
The portion of the electromagnetic spectrum which is visible to the unaided human eye. Also referred to as visible light.
liquefaction
liquid
One of the four fundamental states of matter, characterized by nearly incompressible fluid particles that retain a definite volume but no fixed shape.
London dispersion forces
A type of weak intermolecular force.
Newton's laws of motion
An object in motion stays in motion; an object at rest stays at rest unless an unbalanced force acts upon it.

## M

magnetic quantum number
malleability
See ductility.
manometer
An instrument used to measure pressure invented by Evangelista Torricelli in 1643.
mass
A property of physical matter that is a measure of its resistance to acceleration when a net force is applied. The SI base unit for mass is the kilogram (kg).
mass concentration
mass fraction
mass number
mass spectrometry
matter
Any substance that has mass and takes up space by having volume.
metal
Any chemical element which is a good conductor of both electricity and heat and which readily forms cations and ionic bonds with non-metals.
melting
The phase transition of a substance from a solid to a liquid.
melting point
metalloid
A chemical element or substance possessing properties of both metals and non-metals.
methylene blue
A heterocyclic aromatic compound with the molecular formula C16H18N3SCl.
microcentrifuge tube
A small plastic container that is used to store small amounts of liquid.
mineral
miscibility
mixture
A material made up of two or more different substances which are mixed physically but are not combined chemically (i.e. a chemical reaction has not taken place which has changed the molecules of the substances into new substances).
moiety
molality
molar attenuation coefficient
molar mass
molarity
mole
A measurement of an amount of substance in terms of the absolute number of units or entities composing the substance; a single mole contains approximately 6.022×1023 units or entities. Abbreviated mol.
molecular formula
molecular orbital
The region where an electron can be found in a molecule (as opposed to an atom).
molecular orbital diagram
molecule
A number of atoms that are chemically bonded together and collectively electrically neutral.

## N

natural abundance
neat
conditions with a liquid reagent or gas performed with no added solvent or cosolvent
neutron
A neutral unit or subatomic particle that has no net charge.
neutrino
a particle that can travel at speeds close to the speed of light and are created as a result of radioactive decay
nitrogen
nucleus
The centre of an atom, made up of neutrons and protons and possessing a net positive electric charge.
noble gas
Any of the six non-metallic elements of Group 18 of the periodic table: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). All of the noble gases have outer electron shells that are completely filled in their naturally occurring states, giving them very low chemical reactivity.
non-metal
Any element which is not a metal.
nuclear
Of or pertaining to the atomic nucleus.
nuclear chemistry
The branch of chemistry that studies the various processes and properties relevant to atomic nuclei, including radioactivity.
nuclear magnetic resonance spectroscopy
A technique that exploits the magnetic properties of certain nuclei, useful for identifying unknown compounds. Nuclear magnetic resonance is often abbreviated NMR.
nuclear transmutation
nuclide
A species of atom characterized by its mass number, atomic number, and nuclear energy state, provided that the mean life in that state is long enough to be observable.
number density
A measure of the concentration of countable objects (atoms, molecules, etc.) in space, expressed as the number per unit volume.

## O

octet rule
A classical rule for describing the electron configuration of atoms in certain molecules: the maximum number of electron pairs that can be accommodated in the valence shell of an element in the first row of the periodic table is four (or eight total electrons). For elements in the second and subsequent rows, there are many exceptions to this rule. Also called the Lewis octet rule.
optical activity
orbital
may refer to either an atomic orbital or a molecular orbital
orbital hybridisation
order of reaction
organic acid
organic compound
Any chemical compound that contains carbon. Compare inorganic compound.
organic chemistry
A branch of chemistry concerned with the chemical properties and reactions of organic compounds. Compare inorganic chemistry.
organic redox reaction
osmotic pressure
other metal
metallic elements in the p-block, characterized by having a combination of relatively low melting points (all less than 950 K) and relatively high electronegativity values (all more than 1.6, revised Pauling).
oxidation
oxidation state
1) The degree of oxidation (loss of electrons) of an individual atom in a chemical compound; 2) the hypothetical electric charge (positive, negative, or zero) that the atom would have if all bonds to atoms of different elements were 100% ionic, with no covalent component. Also called oxidation number.
oxidizing agent
oxoacid
1) Any acid having oxygen in the acidic group; 2) any compound which contains oxygen, at least one other element, and at least one hydrogen atom bound to oxygen, and which produces a conjugate base by loss of positive hydrogen ions. Also called an oxyacid or oxacid.
oxygen

## P

p-block
pH
A measure of acidity or basicity of a solution.
pascal
passivation
phase
phase transition
1) A transformation between solid, liquid, and gaseous states of matter and, in rare cases, plasma; 2) the measurable values of the external conditions at which such a transformation occurs.
This diagram shows the nomenclature used for each of the different phase transitions
phi bond
physical chemistry
pi bond
pipette
plasma
One of the four fundamental states of matter, in which very high-energy particles are partially or fully ionized to the point that they display unique properties and behaviors unlike those of the other three states. Plasma does not exist freely on the Earth's surface under natural conditions.
period
One of the horizontal rows of the periodic table and the elements it contains.
periodic table of the elements
A tabular arrangement of the chemical elements organized by their atomic number, electron configuration, and other chemical properties, whose adopted structure shows periodic trends and is used by chemists to derive relationships between various elements as well as predict the properties and behaviors of undiscovered or newly synthesized elements. The first periodic table of the elements was published by Russian chemist Dmitri Mendeleev in 1869. Also simply called the periodic table.
The modern periodic table of the elements. The rows are called periods and the columns are called groups or families.
polarity
potential energy
The stored energy in a body or in a system due to its position in a force field or due to its configuration.
precipitate
The formation of a solid in a solution or inside another solid during a chemical reaction or by diffusion in a solid.
precision
How close the results of multiple experimental trials are. Compare accuracy.
photon
A carrier of electromagnetic radiation of all wavelengths (such as gamma rays and radio waves).
polyatomic ion
A molecule composed of two or more covalently bonded atoms which collectively bear a net electric charge and therefore act as an ion.
proton
A subatomic particle with a positive electric charge that is found in the nucleus of an atom. Often denoted with the symbol H+.
protonation
The addition of a proton (H+) to an atom, molecule, or ion.
pyrolysis
The thermal decomposition of materials at elevated temperatures in an inert atmosphere such as a vacuum gas.

## Q

quantum mechanics
The study of how atoms, molecules, subatomic particles, etc. behave and are structured.
quark
An elementary particle and a fundamental constituent of matter.
quantum
The minimum amount of bundle of energy. Plural quanta.

## R

racemate
An equimolar mixture of a pair of enantiomers which does not exhibit optical activity. The chemical name or formula of a racemate is distinguished from those of the enantiomers by the prefix (±)- or by the symbols RS and SR.
Energy released in the form of waves or subatomic particles when there is a change from high-energy to low-energy states.
The process of an unstable atomic nucleus losing energy by emitting radiation.
Raoult's law
rare-earth metal
rate equation
rate law
reactant
A substance that is consumed in the course of a chemical reaction. Also called a reagent.
reaction mechanism
reaction rate
The speed at which reactants are converted into products in a chemical reaction.
reaction rate constant
reactive intermediate
reactivity series
reagent
A test substance that is added to a system in order to bring about a chemical reaction or to see whether a reaction occurs. Also another name for a reactant.
redox
reducing agent
reduction potential
resonance
retort
rust

## S

s-block
The collective name for the elements in Groups 1 and 2 of the periodic table (the alkali and alkaline metals), as well as hydrogen and helium.
salt
Any ionic compound composed of one or more anions and one or more cations.
salt bridge
A device used to connect reduction with oxidation half-cells in an electrochemical cell.
saline solution
A common term for a solution of sodium chloride (NaCl) dissolved in water (H2O).
Schrödinger equation
A quantum state equation which represents the behaviour of an election around an atom.
scientific theory
second-order reaction
semiconductor
An electrically conductive solid whose degree of conductivity lies somewhere between that of a conductor and that of an insulator.
serial dilution
side chain
single bond
A chemical bond that involves the sharing of one pair of electrons.
sol
A suspension of solid particles in liquid. Artificial examples include sol-gels.
solid
One of the four fundamental states of matter, characterized by relatively low-energy particles packed closely together in rigid structures with definite shape and volume. See Young's modulus.
solubility
The property of a solid, liquid, or gaseous solute to dissolve in a solid, liquid, or gaseous solvent. It is typically expressed as the proportion of solute dissolved in the solvent in a saturated solution.
solute
The part of a solution that is dissolved into the solvent (for example, sodium chloride (NaCl) is the solute in a solution of saline water).
solution
A homogeneous mixture made up of multiple substances generally referred to as solutes and solvents.
solvation shell
solvent
The part of a solution that dissolves the solute (for example, H2O is the solvent in a solution of saline water).
spectrochemistry
spectroscopy
The study of radiation and matter, such as X-ray absorption and emission spectroscopy.
speed of light
A physical constant defined as the speed of anything that has zero rest mass (Energyrest = mc², where m is the mass and c is the speed of light).
standard conditions of temperature and pressure
A standardisation of ambient temperature and pressure used in order to easily compare experimental results. Standard temperature is 25 degrees Celsius (°C) and standard pressure is 100.000 kilopascals (kPa). Standard conditions are often denoted with the abbreviation STP or STAP.
state of matter
matter having a homogeneous, macroscopic phase; gas, plasma, liquid, and solid are the most well-known (in increasing concentration).
stereochemistry
stereoisomer
An isomer which possesses an identical chemical composition but which differs in the spatial arrangement of its atoms.
stoichiometry
structural formula
structural isomer
sublimation
The phase transition of a substance from a solid to a limewater fuel or gas without an apparent transition to a liquid in the process.
subatomic particle
Any particle that is smaller than an atom. Examples include protons, neutrons and electrons.
substance
A material with a definite chemical composition.
substituent

## T

talc
A mineral representing the one on the Mohs Scale and composed of hydrated magnesium silicate with the chemical formula H2Mg3(SiO3)4 or Mg3Si4O10(OH)2.
tarnish
temperature
A proportional measure of the average kinetic energy of the random motions of the constituent microscopic particles of a system. The SI base unit for temperature is the kelvin.
theoretical yield
See yield.
theory
An experimentally testable model describing the nature of a phenomenon.
thermal conductivity
The property of a material that allows it to conduct thermal energy or heat (a quantity often denoted by ${\displaystyle k}$).
thermochemistry
The study of the absorption or release of heat during a chemical reaction.
thermodynamics
The study of the effects of changing temperature, volume or pressure (or work, heat, and energy) on a macroscopic scale.
thermodynamic stability
The condition of a system being in its lowest energy state with its environment (equilibrium).
thermometer
An instrument used to measure temperature.
titration
The process of titrating one solution with another. Also called volumetric analysis.
torr
A unit for measuring pressure (1 torr is equivalent to 133.322 Pa or 1.3158×10−3 atm).
transition metal
An element whose atoms naturally occur with incompletely filled "d" sub-shells. These elements are grouped as the d-block elements in the periodic table.
transuranic element
Any element with an atomic number greater than 92. None of the transuranic elements are stable in natural conditions.
triple bond
A chemical bond that involves the covalent sharing of three pairs of electrons (for example, the diatomic nitrogen molecule, N2, is composed of two nitrogen atoms linked by a triple bond).
triple point
The place where temperature and pressure of three phases are the same (water has a special phase diagram).
A phase diagram showing the triple point and critical point of a substance
Tyndall effect
The effect of light scattering by colloidal (mixture where one substance is dispersed evenly through another) or suspended particles.

## U

UN number
A four-digit code used to note hazardous and flammable substances.
uncertainty
The notion that any measurement that involves estimation of any amount cannot be exactly reproducible.
uncertainty principle
knowing the location of a particle makes the momentum uncertain, while knowing the momentum of a particle makes the location uncertain.
unified atomic mass unit
A unit of mass approximately equal to the mass of one proton or neutron and denoted with the symbol u; also called a Dalton and denoted with the symbol Da. Sometimes equated with the technically distinct and obsolete atomic mass unit and abbreviated amu.
unit cell
The smallest repeating unit of a lattice.
unit factor
statements used in converting between units.
unpaired electron

## V

An insulating storage vessel that can greatly lengthen the time over which its contents remain warmer or cooler than the vessel's ambient environment. Also called a Dewar flask or thermos.
valence electron
Any of the outermost electrons of an atom, which are located in electron shells.
valence bond theory
A theory explaining the chemical bonding within molecules by discussing valencies, the number of chemical bonds formed by an atom.
valency
The combining capacity of an element.
van der Waals force
One of the forces (attraction/repulsion) between molecules.
van 't Hoff factor
The ratio of moles of particles in solution to moles of solute dissolved.
vapor
When a substance is below the critical temperature while in the gas phase.
vapor pressure
The pressure of vapor over a liquid at equilibrium.
vaporization
The phase transition of a substance from a liquid to a gas. Also called boiling.
viscosity
A measure of the resistance of a liquid to flow.
volt
A unit that measures the electrical potential transferred. One volt (V) is defined as and equivalent to one Joule of work per coulomb.
voltmeter
An instrument that measures electrical cell potential.
volume
The quantity of three-dimensional space enclosed by a closed surface, or the space that a substance (solid, liquid, gas, or plasma) or shape occupies or contains. The SI unit for volume is the cubic metre (m3).
volumetric analysis
See titration.

## W

watch glass
water
A polar inorganic compound with the chemical formula H2O that is a tasteless, odorless, and generally colorless liquid at standard temperature and pressure, though it also occurs naturally as a solid and a gas at the Earth's surface. It is the most abundant substance on Earth and therefore an integral component of virtually all chemical and biological systems. Water is often described as the "universal solvent" for its inherent ability to dissolve many substances.
wave function
a function describing the electron's position in a three-dimensional space.
work
the amount of force over distance and is in terms of joules (energy).

## X

X-ray
A form of ionizing, electromagnetic radiation between gamma and UV rays in the electromagnetic spectrum.
X-ray diffraction
a method for establishing structures of crystalline solids using single wavelength X-rays and looking at diffraction pattern.
X-ray photoelectron spectroscopy
A spectroscopic technique used to measure the composition of a material.

## Y

yield
The quantifiable amount of product produced during a chemical reaction.

## Z

zone melting
A way to remove impurities from an element by melting it and slowly travel down an ingot (cast).
zwitterion
A chemical compound whose net charge is zero and hence is electrically neutral. But there are some positive and negative charges in it, due to the formal charge, owing to the partial charges of its constituent atoms.
zinc
A metallic chemical element with atomic number 30 and symbol Zn.