Level 3 Thermochemistry

Ionisation energy

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

Atomic radius

Measure of the size of an atom - usually involving the average distance from the nucleus to the outermost 'cloud' of electrons.

Electronegativity

A measure of the tendency of an atom to attract a bonding pair of electrons.

Non polar molecule

A molecule that may contain polar bonds, but because of their arrangement has no overall molecular dipole (polar bonds cancel).

Polar molecule

A molecule with overall charge separation (dipole) due to the existence of polar bonds.

Temporary dipole (induced dipole) attraction

The separation of charge produced in an atom or molecule by a momentary uneven distribution of electrons which results in temporary forces with neighbouring molecules.

Permanent dipole-dipole attraction

An attractive force between permanent dipoles in neighbouring polar molecules.

hydrogen bonding

The intermolecular force in which a hydrogen atom that is bonded to a highly electronegative atom (F, O or N) is attracted to an unshared pair of electrons of an electronegative atom in a nearby molecule. This is the strongest intermolecular force.

Enthalpy of fusion

The amount of energy absorbed to change 1 mole of a substance from a solid to a liquid at it's melting point.

Enthalpy of sublimation

The energy required to convert one mole of a substance from a solid to a gas

Enthalpy of vaporization

The energy required to convert 1 mole of a substance from a liquid to a gas at it's boiling point.

Entropy

A measure of disorder or randomness.

Enthalpy of combustion

The enthalpy change that occurs during the complete combustion of one mole of a substance

Enthalpy of formation

The enthalpy change that occurs when 1 mole of a substance is formed from its pure elements under standard conditions.

Octaherdral

Molecular shape where the central atom has 6 areas of electron density and 6 bonded atoms

Square pyramidal

Molecular shape where the central atom has 6 areas of electron density with 5 bonded atoms and one lone pair of electrons

Square planar

Molecular shape where the central atom has 6 areas of electron density with 4 bonded atoms and two lone pairs of electrons

Trigonal bipyramidal

Molecular shape where the central atom has 5 areas of electron density with 5 bonded atoms

See-saw

Molecular shape where the central atom has 5 areas of electron density with 4 bonded atoms and one lone pair of electrons

T-shaped

Molecular shape where the central atom has 5 areas of electron density with 3 bonded atoms and two lone pairs of electrons

Trend in ionisation energy

Increases as you go across and row. Decreases down a period.

trend of atomic radius

Decreases across a row. Increases down a period.

trend of electronegativity

Increases across a row. Decreases down a period.