Atomic Structure, Periodic Trends, Bonding and Matter

Atom

The smallest particle of an element that retains its chemical properties.

Proton

A positively charged particle found in the nucleus.

Neutron

A neutral particle found in the nucleus.

Electron

A negatively charged particle found in electron shells and subshells around the nucleus.

Atomic number

The number of protons in an atom's nucleus.

Mass number

The total number of protons and neutrons in an atom's nucleus.

Isotope

Atoms of the same element with the same number of protons but different numbers of neutrons.

Ion

An atom or group of atoms with an electrical charge due to gaining or losing electrons.

Cation

A positively charged ion formed by losing electrons.

Anion

A negatively charged ion formed by gaining electrons.

Polyatomic ion

A group of covalently bonded atoms carrying an overall charge.

Electron configuration

The arrangement of electrons in an atom's shells and subshells.

Valence electrons

Electrons in the outermost occupied electron shell.

Relative atomic mass (Ar)

The weighted average mass of an element's atoms relative to one-twelfth of a carbon-12 atom.

First ionisation energy

The energy required to remove one electron from each atom in one mole of gaseous atoms.

Electronegativity

The ability of an atom to attract shared electrons in a chemical bond.

Atomic radius

A measure of the size of an atom.

Core charge

The net positive charge experienced by valence electrons due to the nucleus and inner-shell electrons.

Emission spectrum

A pattern of specific wavelengths of light emitted by excited atoms.

Absorption spectrum

A spectrum with specific wavelengths missing because atoms absorb those wavelengths of light.

Atomic absorption spectroscopy (AAS)

A technique that measures light absorbed by atoms to determine the concentration of an element.

Mass spectrometry

A technique that separates ions according to their mass-to-charge ratio to identify isotopes or substances.

Mass-to-charge ratio (m/z)

The mass of an ion divided by its charge.

John Dalton

Proposed that matter consists of atoms and developed an early atomic theory.

J. J. Thomson

Discovered the electron and proposed the plum pudding model.

Ernest Rutherford

The gold foil experiment showed that atoms contain a small, dense, positively charged nucleus.

Niels Bohr

Proposed that electrons occupy specific, quantised energy levels.

James Chadwick

Discovered the neutron.

Pure substance

Matter consisting of only one chemical substance, either an element or a compound.

Element

A pure substance containing only one type of atom.

Compound

A substance containing two or more elements chemically bonded in fixed proportions.

Mixture

Two or more substances physically combined in variable proportions.

Homogeneous mixture

A mixture with a uniform composition throughout.

Heterogeneous mixture

A mixture with a non-uniform composition.

Allotrope

One of two or more structural forms of the same element.

Nanomaterial

A material with structural features on the nanoscale, typically around 1-100 nm.

Percentage composition

The percentage by mass of a particular element in a compound.

Filtration

Separates an insoluble solid from a fluid using a porous barrier.

Evaporation

Removes a solvent by converting it into a gas.

Crystallisation

Forms solid crystals from a solution, often by cooling or evaporating solvent.

Distillation

Separates substances using differences in boiling points and condensation.

Separating funnel

Separates immiscible liquids based on their different densities.

Magnetic separation

Separates magnetic materials from non-magnetic materials.

Diamond

Carbon atoms each bond to four others in a 3D covalent network; very hard, high melting point, and does not conduct electricity.

Graphite

Carbon atoms form layers of hexagonal rings; layers slide easily and delocalised electrons allow electrical conductivity.

Fullerenes

Carbon atoms form hollow cages or tubes; properties depend on their structure.

Chemical bond

An attraction that holds atoms or ions together.

Valency

The combining capacity of an atom, related to the number of bonds it can form.

Ionic bonding

Electrostatic attraction between oppositely charged ions in a lattice.

Covalent bonding

Attraction between nuclei and shared pairs of electrons.

Metallic bonding

Attraction between positive metal ions and delocalised electrons.

Covalent molecular substance

A substance made of discrete molecules with covalent bonds within each molecule.

Covalent network substance

A substance consisting of atoms joined by an extensive covalent network.

Intermolecular forces

Attractions between separate molecules.

Hydrocarbon

A compound containing only carbon and hydrogen.

Alkane

A saturated hydrocarbon containing only carbon-carbon single bonds.

Alkene

An unsaturated hydrocarbon containing at least one carbon-carbon double bond.

Benzene

A six-carbon aromatic ring with delocalised electrons.

Saturated

Contains only carbon-carbon single bonds.

Unsaturated

Contains at least one carbon-carbon double or triple bond.

Structural formula

A representation showing how atoms are arranged and bonded in a molecule.

IUPAC nomenclature

A systematic set of rules used to name chemical compounds.

Combustion

A reaction with oxygen that releases energy.

Complete combustion

Burning with sufficient oxygen to produce carbon dioxide and water from a hydrocarbon.

Incomplete combustion

Burning with insufficient oxygen, potentially producing carbon monoxide and/or carbon alongside water.

Addition reaction

A reaction where atoms add across a carbon-carbon double bond.

Substitution reaction

A reaction where one atom or group is replaced by another.

Stoichiometry

Calculations involving quantitative relationships between reactants and products.

Mole

An amount of substance containing 6.022 × 10²³ specified particles.

Avogadro's constant

6.022 × 10²³ mol⁻¹, the number of specified particles in one mole.

Molar mass

The mass of one mole of a substance, measured in g mol⁻¹.

Mole ratio

The ratio of amounts of substances given by coefficients in a balanced chemical equation.

Limiting reagent

The reactant consumed first, which limits the amount of product formed.

Excess reagent

A reactant remaining after the limiting reagent is completely consumed.

Empirical formula

The simplest whole-number ratio of atoms of each element in a compound.

Molecular formula

The actual number of atoms of each element in one molecule.

Water of crystallisation

Water incorporated into the crystal structure of a substance.

Hydrated salt

A salt containing water of crystallisation.

Law of Conservation of Mass

Matter is conserved during a chemical reaction; atoms are rearranged, not created or destroyed.

Chemical reaction

A process in which reactants become products through rearrangement of atoms and chemical bonds.

Balanced chemical equation

An equation with equal numbers of each type of atom on both sides.

Enthalpy change (ΔH)

The heat energy transferred by a system at constant pressure.

Exothermic reaction

Transfers energy to the surroundings; ΔH is negative.

Endothermic reaction

Absorbs energy from the surroundings; ΔH is positive.

Activation energy

The minimum energy particles must have for a reaction to occur.

Bond breaking

Requires energy.

Bond forming

Releases energy.

Fossil fuel

A fuel formed over geological time from ancient organic matter.

Biofuel

A fuel produced from biological material, such as plants or organic waste.

Catalyst

Increases reaction rate by providing an alternative pathway with lower activation energy and is not consumed overall.

Decomposition reaction

One compound breaks down into simpler substances.

Displacement reaction

One element replaces another element in a compound.

Oxidation

Involves loss of electrons; often involves gain of oxygen.

Reduction

Involves gain of electrons; often involves loss of oxygen.

Rate of reaction

Change in the amount or concentration of a reactant or product per unit time.

Collision theory

Particles must collide with sufficient energy and suitable orientation for a reaction to occur.

Effective collision

A collision that results in a chemical reaction.

Concentration

The amount of solute per volume of solution.

Surface area

The area of a solid exposed to other reactants.

Catalytic converter

A vehicle exhaust device that uses catalysts to reduce harmful emissions.