OCR A A-Level Chemistry Definitions Module 2 - Foundations in Chemistry

Relative Atomic Mass

The average mass of an atom relative to the mass of one twelfth of a Carbon-12 atom.

Relative Molecular Mass

The mads of a molecule relative to the mass of one twelfth of a Carbon-12 atom.

Relative Formula Mass

The mass of a formula of the compound relative to the mass of one twelfth of a Carbon-12 atom.

Relative Isotopic Mass

The mass of one atom of a particular isotope relative to the mass of one one twelfth of a Carbon-12 atom.

The Mole

One mole of a substance is the mass that has the same number of particles as there are in exactly 12g of Carbon-12.

Avagadro's Constant

The number of atoms or molecules in one mole of a substance (6.01 * 10^23)

Molar Mass

The mass of one mole of a substance

Empirical Formula

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

Molecular Formula

Shoes the total number of atoms of each element present in a molecule of the compound.

Isotopes

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

First Ionisation Energy

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

Ionic Bonding

The electrostatic attraction between two oppositely charged ions.

A Covalent Bond

The bond formed when two atoms share a pair of electrons.

A Dative Covalent Bond

A covalent bond where both electrons come from the same atom.

Metallic Bond

The electrostatic attraction between the positive metal ions and the negative 'sea' of mobile electrons.

Electronegativity

The ability of an atom to attract the bonding pair of electrons in a covalent bond.

Oxidation

The loss of electrons from an atom or an ion.

Reduction

The gain of electrons by an atom or an ion.

Disproportionation

Where a species is simultaneously oxidised and reduced in the same reaction.

Acid

A species that is a proton donor.

Alkali

A species that is a proton acceptor.

Salt

A compound formed from an acid when a H+ ion from the acid has been replaced by a metal ion or another positive ion such as the ammonium ion NH4+.