2 - Atoms, elements and compounds

Element

A pure substance made up of atoms that cannot be broken down any further.

Compound

Two or more elements chemically combined together.

Mixture

Two or more substances that are not chemically combined together.

Ion

A charged particle formed by atoms losing or gaining electrons.

Molecule

A group of atoms bonded together; the smallest unit of a chemical compound that can take part in a chemical reaction.

Atom

The smallest unit of an element that retains its chemical properties, comprised of neutrons, protons, and electrons.

Proton/atomic number

The number of protons in the nucleus of an atom.

Mass/Nucleon number/atomic mass

The number of protons and neutrons in the nucleus of an atom.

Stable atom

An atom where the number of protons equals the number of electrons.

Isotope

Atoms of the same element that differ in the number of neutrons.

Relative atomic mass (Ar)

The mass of an isotope of an element compared to 1/12th of the mass of a Carbon-12 atom.

Relative molecular mass (Mr)

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

Ionic bonding

The formation of a chemical bond between oppositely charged ions, often between metals and non-metals.

Ionic lattice

A regular arrangement of alternating positive and negative ions in an ionic compound.

Covalent bonding

The interatomic linkage that results from the sharing of an electron pair between two atoms.

Allotrope

One or more forms of a chemical element that can exist in the same physical state.

Graphite

An allotrope of carbon where each carbon is bonded to 3 other carbons, allowing for conductivity.

Diamond

An allotrope of carbon in which each carbon is bonded to 4 others, resulting in hardness and no electrical conductivity.

Intramolecular forces

Forces within a molecule that keep the molecule together.

Intermolecular forces

Attractions between molecules that determine the physical properties of a substance.