AS Chemistry definitions

Molecular ion

Two or more atoms covalently bonded with an overall charge

Avogardo’s constant

The number of atoms in 12.000g of carbon-12

A Mole

The amount of a substance that contains the Avogardo constant of atoms, molecules or groups of ions

Molar mass

The mass of one mole of a substance

Anhydrous salt

A salt that contains no water of crystallisation

Hydrated salt

A salt that contains water of crystallisation

Water of crystallisation

Water chemically bonded within a crystal structure

Atomic number

The number of protons in the nucleus of an atom

Mass number

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

Relative Atomic Mass

The average weighed mean mass of an atom of an element relative to one-twelfth of the mass of an atom of carbon-12

Relative Isotopic Mass 

The mass of an atom of an isotope of an element relative to one-twelfth of the mass of an atom of carbon-12

Relative Formula Mass

The average weighted mean mass of a formula unit relative to one-twelfth of the mass of an atom of carbon-12

Relative Molecular Mass

The average weighted mean mass of a molecule relative to one-twelfth of the mass of an atom of carbon-12

Isotopes

Atoms which have the same atomic number but a different mass number

Orbital

a region of space within a shell which can hold up to two electrons with opposite spins

S block subshell

An S block element has its outer electron in the s subshell

First ionisation energy

The energy required to convert one mole of gaseous atoms into gaseous ions with a single positive charge

Second ionisation energy

The energy required to convert one mole of gaseous ions with a single positive charge into gaseous ions with a double positive charge

Third ionisation energy

The energy required to convert one mole of gaseous ions with a double positive charge into gaseous ions with a triple positive charge

Ionic bonding

Ionic bonds form between metal and non-metal ions

Covalent bond

The electrostatic attraction between a shared pair of electrons and the nuclei of bonded atoms

Octet rule

When reacting, an atom tends to gain, lose or share electrons to achieve eight in its outer shell

Coordinate bond

A shared pair of electrons between two atoms. One atom provides both electrons

Electronegativity

The extent to which an atom attracts the bonding electrons in a covalent bond 

Polar bond 

A covalent bond in which there is unequal sharing of the bonding electrons

Intermolecular

Between neighbouring molecules

Hydride

An element bonded to hydrogen