Lattice enthalpies of formation always have negative values because the process is exothermic, as new bonds are formed between the oppositely charged ions.

The more negative the lattice enthalpy value, the stronger the ionic bonding.

Enthalpy change of atomisation is the enthalpy change when one mole of gaseous atoms is formed from the element in its standard state under standard conditions.

For example, the equation for the enthalpy change of atomisation of Na is: Na_(s) ➔ Na_(g).

$\frac{1}{2}$Cl_2(g) ➔ Cl_(g)

Bond enthalpy is the enthalpy change when one mole of a particular covalent bond in the gaseous state is broken.

First electron affinity is the enthalpy change when one mole of gaseous atoms gains one electron to form one mole of gaseous ions with a charge of -1.

For example, the equation for the first electron affinity of F is: F_(g) + e^- ➔ F^-_(g).

S_(g) + e^- ➔ S^-_(g)

First ionisation energies are endothermic because energy must be supplied to overcome the electrostatic attraction between the nucleus and the electron being removed.

MgO_(s) ➔ Mg²⁺_(g) + O^2-_(g)

Lattice enthalpy of formation is the enthalpy change that occurs when one mole of an ionic compound is formed from its gaseous ions under standard conditions.

For example, the equation for the lattice enthalpy of formation of NaCl is:

Na⁺_(g) + Cl^-_(g) ➔ NaCl_(s)