WACE Chemistry ATAR key terms

The number of protons in the nucleus of an atom, which uniquely identifies the element and equals the number of electrons in a neutral atom.

The total number of protons and neutrons in the nucleus of one atom, giving the approximate relative atomic mass of that particular atom.

Atoms of the same element with identical proton numbers but different neutron numbers, so they share chemical properties yet differ in mass and sometimes nuclear stability.

The weighted average mass of an element's atoms compared with one-twelfth the mass of a carbon-12 atom, accounting for the natural abundance of each isotope.

The electrons occupying the outermost occupied shell of an atom, which are chiefly responsible for bonding behaviour and determine the element's group chemistry.

The minimum energy needed to remove one mole of electrons from one mole of gaseous atoms or ions, measured in kilojoules per mole.

A measure of how strongly an atom attracts shared bonding electrons within a molecule; values increase across a period and decrease down a group.

The electrostatic attraction holding oppositely charged ions together in a lattice, formed when electrons are transferred from a metal to a non-metal.

A bond formed when two atoms share one or more pairs of electrons, typically between non-metal atoms, producing discrete molecules or network structures.

A covalent bond in which electron density is unevenly shared because the bonded atoms differ in electronegativity, creating partial positive and partial negative charges.

A model predicting molecular shape by assuming electron pairs around a central atom repel each other and arrange themselves as far apart as possible.

The angle between two adjacent covalent bonds at a central atom, determined by electron-pair repulsion and useful for identifying molecular geometry.

A measure of molecular polarity arising from unequal charge distribution; it depends on both bond polarity and the overall geometry of the molecule.

The amount of substance containing 6.022 x 10^23 representative particles, used to convert between particle numbers, masses and gas volumes.

The mass in grams of one mole of a substance, numerically equal to its relative formula mass and used to convert mass to amount.

The reactant that is completely consumed first in a chemical reaction, thereby determining the maximum amount of product that can form.

The actual mass of product obtained expressed as a percentage of the theoretical mass predicted by stoichiometry, indicating reaction efficiency.

The simplest whole-number ratio of atoms of each element present in a compound, derived from percentage composition or combustion data.

A species that donates a proton (hydrogen ion) to another species in a reaction, forming its conjugate base once the proton is released.

Two species related by the transfer of a single proton, such as an acid and the base formed after it loses that proton.

A logarithmic scale defined as the negative logarithm to base ten of hydrogen ion concentration, expressing how acidic or basic a solution is.

An acid that ionises essentially completely in water, producing a high concentration of hydrogen ions and a very low pH.

A solution containing a weak acid and its conjugate base that resists significant pH change when small amounts of acid or base are added.

The loss of electrons by a species, accompanied by an increase in oxidation number; it occurs at the anode in an electrochemical cell.

The gain of electrons by a species, accompanied by a decrease in oxidation number; it occurs at the cathode in an electrochemical cell.

A bookkeeping value assigned to an atom in a compound representing its apparent charge, calculated from electronegativity-based rules and used to identify redox changes.

The voltage of a half-cell measured against the standard hydrogen electrode under standard conditions, used to predict the direction of redox reactions.

An electrochemical cell in which an external power supply drives a non-spontaneous redox reaction, used for processes such as electroplating and metal extraction.

The heat energy exchanged with the surroundings during a reaction at constant pressure, given the symbol delta H and usually measured in kilojoules per mole.

The minimum energy that colliding particles must possess for a reaction to occur, corresponding to the energy barrier between reactants and products.

The average energy required to break one mole of a particular covalent bond in the gaseous state, used to estimate reaction enthalpy changes.

A model stating that particles must collide with sufficient energy and correct orientation for a reaction to occur, explaining how concentration and temperature affect rate.

A substance that increases the rate of a reaction by providing an alternative pathway with lower activation energy, without being consumed overall.

The state in a closed system where forward and reverse reaction rates are equal, so concentrations stay constant although both reactions continue.

A rule stating that when a system at equilibrium is disturbed, the position of equilibrium shifts to partially oppose the change applied.

The ratio of product concentrations to reactant concentrations, each raised to its stoichiometric coefficient, at equilibrium at a stated temperature.

A specific group of atoms within an organic molecule that gives the compound its characteristic chemical properties and reactions.

A family of organic compounds sharing the same functional group and general formula, with successive members differing by one CH2 unit.

Compounds with the same molecular formula but different arrangements of atoms, leading to different physical or chemical properties.

A volumetric procedure in which a solution of known concentration is added from a burette to a measured volume of analyte until the equivalence point is reached.

The point in a titration where the amount of titrant added exactly matches the amount required to react completely with the analyte in the balanced equation.

A solution whose concentration is accurately known, prepared by weighing a pure primary standard or by diluting a stock solution precisely.

A separation technique in which components distribute differently between a mobile phase and a stationary phase, allowing identification and sometimes quantification.