What factors affect the value of lattice enthalpy?

The factors affecting lattice enthalpy values are:

  1. Ionic charge.
  2. Ionic radius.


Lattice enthalpy becomes more negative as ionic charge increases and ionic radius decreases.

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What is the link between ionic bond strength and lattice enthalpy?

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

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Define enthalpy change of atomisation (ΔH⦵at).

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).

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What is the equation that represents the enthalpy change of atomisation of chlorine?

12\frac{1}{2}Cl2(g) ➔ Cl(g)

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Define first electron affinity (ΔH⦵ea1).

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).

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What is the equation for the first electron affinity of sulfur?

S(g) + e- ➔ S-(g)

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Why are first ionisation energies endothermic?

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

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What factors affect electron affinity values?

The factors affecting electron affinity values are:

  1. Nuclear charge.
  2. Atomic radius.
  3. Electron shielding.

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State and explain the general trend in first electron affinity as we move down groups 16 and 17.

First electron affinity generally becomes less negative (less exothermic) as you move down groups 16 and 17.


This is due to the combined effects of increasing atomic radius and increasing shielding of the nucleus by the inner electron shells. These effects outweigh the increase in nuclear charge, resulting in a weaker attraction between the nucleus and the incoming electron as you move down the groups.

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Explain why fluorine is an exception to the general trend of decreasing first electron affinitity as you move down group 17.


Unlike the other elements in the group, fluorine has a less exothermic (less negative) first electron affinity than chlorine.


This is due to fluorine's small atomic radius, which causes increased electron-electron repulsion between the added electron and the existing outer shell electrons due to their proximity. As a result, less energy is released when an electron is added to fluorine compared to chlorine, leading to its less exothermic first electron affinity.

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Define lattice energy (ΔH⦵latt).

Lattice energy 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 energy of NaCl is:

Na+(g) + Cl-(g) ➔ NaCl(s)

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Explain whether lattice enthalpies have positive or negative values.

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

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