abbreviated electron configuration

An electron configuration that uses one of the noble gases to represent the core of electrons up to that element.

absolute zero

The minimum possible temperature, labelled 0 K (zero kelvins).


An ionic compound of the H+ cation dissolved in water.

activity series

A list of elements that will replace elements below them in single-replacement reactions.

actual yield

The amount that is actually produced in a chemical reaction.

angular momentum quantum number (ℓ)

An index that affects the energy and the spatial distribution of an electron in an atom.


A species with an overall negative charge.

atmosphere (atm)

A unit of pressure equal to the average atmospheric pressure at sea level; defined as exactly 760 mmHg.


The smallest piece of an element that maintains the identity of that element.

atomic mass

The weighted average of the masses of the isotopes that compose an element.

atomic mass unit

One-twelfth of the mass of a carbon-12 atom.

atomic number

The number of protons in an atom.

atomic radius

An indication of the size of an atom.

atomic symbol

A one- or two-letter representation of the name of an element.

atomic theory

The concept that atoms play a fundamental role in chemistry.

aufbau principle

The way that electrons fill the lowest energy orbitals first. From the German for "building up."

Avogadro’s law

A gas law that relates number of particles to volume.

balanced chemical equation

A condition when the reactants and products of a chemical equation have the same number of atoms of all elements present.


A compound that increases the amount of OH− ions in an aqueous solution.

Boyle’s law

A gas law that relates pressure and volume at constant temperature and amount.


A unit of energy measurement originally defined in terms of warming up a given quantity of water. 1 cal = 4.184 J


A container used to measure the heat of a chemical reaction.


The process of measuring enthalpy changes in chemical reactions.


A species with an overall positive charge.

Charles’s law

A gas law that relates volume and temperature at constant pressure and amount.

chemical change

The process of demonstrating a chemical property.

chemical equation

A concise way of representing a chemical reaction.

chemical property

A characteristic that describes how matter changes form in the presence of other matter.


The study of the interactions of matter with other matter and with energy.


The raised number to the right of a 10 indicating the number of factors of 10 in the original number.

combined gas law

A gas law that combines pressure, volume, and temperature.

complete ionic equation

A chemical equation in which the dissolved ionic compounds are written as separated ions.

composition reaction

A chemical reaction in which a single substance is produced from multiple reactants.


A combination of more than one element.

compressibility factor

A measure of the extent of deviation from ideal gas behaviour.

continuous spectrum

An image that contains all colours of light.

conversion factor

A fraction that can be used to convert a quantity from one unit to another.

covalent bond

A chemical bond formed by two atoms sharing electrons.

d block

The columns of the periodic table in which d subshells are being occupied.

Dalton’s law of partial pressures

The total pressure of a gas mixture, P_tot, is equal to the sum of the partial pressures of the components, P_i.

decomposition reaction

A chemical reaction in which a single substance becomes more than one substance.


The unit of temperature scales.

derived unit

A unit that is a product or a quotient of a fundamental unit.


The movement of gas molecules through one or more additional types of gas via random molecular motion.

double-replacement reaction

A chemical reaction in which parts of two ionic compounds are exchanged.

effective nuclear charge

The net nuclear charge felt by valence electrons. Denoted as Z_eff ("zed-effective").


The movement of gas molecules from one container to another via a tiny hole.

electromagnetic spectrum

The full span of the possible wavelengths, frequencies, and energies of light.


A tiny subatomic particle with a negative charge.

electron affinity (EA)

The energy change when a gas-phase atom accepts an electron.

electron configuration

A listing of the shell and subshell labels.

electron shell

A term used to describe electrons with the same principal quantum number.


A substance that cannot be broken down into simpler chemical substances by ordinary chemical means.


A chemical reaction that has a positive change in enthalpy.


The ability to do work.

enthalpy change

The heat of a process at constant pressure. Denoted as ΔH.

enthalpy of formation

The enthalpy change for a formation reaction; denoted as ΔHf.

exact number

A number from a defined relationship that technically has an infinite number of significant figures.


A chemical reaction that has a negative change in enthalpy.


A test of the natural universe to see if a guess (hypothesis) is correct.


The raised number to the right of a 10 indicating the number of factors of 10 in the original number.

f block

The columns of the periodic table in which f subshells are being occupied.

formation reaction

A chemical reaction that forms one mole of a substance from its constituent elements in their standard states.


The number of cycles of light that pass a given point in one second.

fundamental units

One of the seven basic units of SI used in science.

gas law

A simple mathematical formula that allows one to model, or predict, the behaviour of a gas.

Gay-Lussac’s law

A gas law that relates pressure with absolute temperature.

Graham’s law of effusion

A law that relates the rate of effusion of a gas to the inverse of the square root of its molar mass.


The transfer of energy from one body to another due to a difference in temperature.

Hess’s law

When chemical equations are combined algebraically, their enthalpies can be combined in exactly the same way.

heterogeneous mixture

A non-uniform combination of more than one substance.

homogeneous mixture

A uniform mixture of more than one substance that behaves as a single substance.

Hund’s rule

One electron is placed in each degenerate orbital before pairing electrons in the same orbital.

hydronium ion

The actual chemical species that represents a hydrogen ion in aqueous solution.


An educated guess about how the natural universe works.

ideal gas

A gas that conforms exactly to the tenets of the kinetic molecular theory.

ideal gas law

A gas law that relates all four independent physical properties of a gas under any conditions.


A species with an overall electric charge.

ionic bond

The attraction between oppositely charged ions.

ionic compound

A compound formed from positive and negative ions.

ionization energy (IE)

The amount of energy required to remove an electron from an atom in the gas phase.

isolated system

A system that does not allow a transfer of energy or matter into or out of itself.


Atoms of the same element that have different numbers of neutrons.


The SI unit of energy.


The fundamental unit of temperature in SI.

kinetic energy

Energy due to motion.

kinetic molecular theory of gases

A model that helps us understand gases and their physical properties at the molecular level.

lattice energy

The measured strength of ionic bonding.

law of conservation of energy

Law of physics that states that the total energy of an isolated system does not increase or decrease.

Lewis diagram

A representation of the valence electrons of an atom that uses dots around the symbol of the element.

limiting reagent

The reactant that runs out first for a given chemical reaction.

magnetic quantum number (mℓ)

The index that determines the orientation of the electron’s spatial distribution.

mass number

The sum of the number of protons and neutrons in a nucleus.

mass-mass calculation

A calculation in which you start with a given mass of a substance and calculate the mass of another substance involved in the chemical equation.


Anything that has mass and takes up space.

mean free path

The average distance travelled by a molecule between collisions.


An element that conducts electricity and heat well and is shiny, silvery, solid, ductile, and malleable.

millimetre of mercury (mmHg)

The amount of pressure exerted by a column of mercury exactly 1 mm high. Approximately 1 mmHg is equal to 1 torr.


A physical combination of more than one substance.

molar mass

The mass of 1 mol of a substance in grams.

molar volume

The volume of exactly 1 mol of a gas; equal to 22.4 L at STP.


The number of things equal to the number of atoms in exactly 12 g of carbon-12; equals 6.022 × 10 to the power of 23 things.

mole fraction

The ratio of the number of moles of a component to the total number of moles in a system.

mole-mass calculation

A calculation in which you start with a given number of moles of a substance and calculate the mass of another substance involved in the chemical equation, or vice versa.

mole-mole calculation

A stoichiometry calculation in which one starts with moles of one substance and converts to moles of another substance using the balanced chemical equation.

molecular mass

The sum of the masses of the atoms in a molecule.

net ionic equation

A chemical equation with the spectator ions removed.

neutralization reaction

The reaction of an acid with a base to produce water and a salt.


A subatomic particle with no charge.


An element that exists in various colors and phases, is brittle, and does not conduct electricity or heat well.

nuclear model

The model of an atom that has the protons and neutrons in a central nucleus with the electrons in orbit about the nucleus.


The centre of an atom that contains protons and neutrons.

numerical prefix

A prefix used with a unit that refers to a multiple or fraction of a fundamental unit to make a more conveniently sized unit for a specific quantity.

octet rule

The trend that atoms like to have eight electrons in their valence shell.


The specific set of principal, angular momentum, and magnetic quantum numbers for an electron.


The loss of one or more electrons by an atom; an increase in oxidation number.

oxidation number

A number assigned to an atom that helps keep track of the number of electrons on the atom.

oxidation-reduction (redox) reactions

A chemical reaction that involves the transfer of electrons.

p block

The columns of the periodic table in which p subshells are being occupied.

partial pressure

The pressure that an individual gas in a mixture has.

Pauli exclusion principle

No two electrons in an atom can have the same set of four quantum numbers.

percent yield

Actual yield divided by theoretical yield times 100%, which gives a percentage between 0% and 100%.

periodic table

A chart of all the elements.

periodic trends

The variation of properties versus position on the periodic table.


An important physical property that defines whether matter is a solid, liquid, gas or supercritical fluid. Also known as a state.


The name of a discrete unit of light acting as a particle.

physical change

A change that occurs when a sample of matter changes one or more of its physical properties.

physical property

A characteristic that describes matter as it exists.

Planck’s constant

The proportionality constant between the frequency and the energy of light: 6.626 × 10 to the power of −34 J·s.


A solid that falls out of solution in a precipitation reaction.

precipitation reaction

A chemical reaction in which two ionic compounds are dissolved in water and form a new ionic compound that does not dissolve.


Force per unit area.

principal quantum number (n)

The index that largely determines the energy of an electron in an atom.


A final substance in a chemical equation.


A subatomic particle with a positive charge.


A description of the quality of an object.


A description of a specific amount of something.


When a quantity is restricted to having only certain values.

quantum mechanics

The theory of electrons that treats them as a wave.

quantum number

An index that corresponds to a property of an electron, like its energy.


An initial substance in a chemical equation.

real gas

A gas that deviates from ideal behaviour.


The gain of one or more electrons by an atom; a decrease in oxidation number.

root-mean-square (rms) speed

The speed of molecules having exactly the same kinetic energy as the average kinetic energy of the sample.

s block

The columns of the periodic table in which s subshells are being occupied.


The process of knowing about the natural universe through observation and experiment.

scientific notation

An expression of a number using powers of 10.


An element that has properties of both metals and nonmetals.

significant figures

The limit of the number of places a measurement can be properly expressed with.

single-replacement reaction

A chemical reaction in which one element is substituted for another element in a compound.

solubility rules

General statements that predict which ionic compounds dissolve and which do not.

specific heat capacity

The proportionality constant between heat, mass, and temperature change; also called specific heat.

spectator ion

An ion that does nothing in the overall course of a chemical reaction.

spin quantum number

The index that indicates one of two spin states for an electron.

standard notation

A straightforward expression of a number.

standard temperature and pressure (STP)

A set of benchmark conditions used to compare other properties of gases: 100 kPa for pressure and 273 K for temperature.


The relating of one chemical substance to another using a balanced chemical reaction.


A term used to describe electrons in a shell that have the same angular momentum quantum number.


Matter that has the same physical and chemical properties throughout.


The part of the universe that is under study.


A measure of the average amount of kinetic energy a system contains.

theoretical yield

An amount that is theoretically produced as calculated using the balanced chemical reaction.


A general statement that explains a large number of observations.

thermochemical equation

A chemical equation that includes an enthalpy change.

valence electron

An electron in the highest-numbered shell or in the last unfilled subshell. Valence electrons are those that are most likely to be involved in chemical reactions.

valence shell

The highest-numbered shell in an atom that contains electrons.

van der Waals equation

An equation that compensates for deviations from ideal gas behaviour, correcting for intermolecular forces and the volume of gas molecules.

vapour pressure

The partial pressure exerted by evaporation of a liquid.


The distance between corresponding points in two adjacent light cycles.