Ionisation Energy

Explain the term first ionisation energy

The energy needed to remove one electron from each atom in one mole of gaseous atoms to form one mole of 1+ gaseous ions.

Write an equation to represent the first ionisation energy of sodium

Na(g) -> Na+(g) + e-

Explain why the first ionisation energy of sodium is an endothermic process

Energy is required to overcome the attraction between the positive nucleus and the negative electron being removed.

State and explain the trend in first ionisation energy down a group

Decreases down a group because atomic radius and electron shielding increase, overriding the increase in nuclear charge and resulting in weaker nuclear attraction for the outer electron.

Explain why the first ionisation energy of Mg is greater than the first ionisation energy of K

Mg has a smaller atomic radius, less electron shielding, and greater nuclear attraction for its outer electron than K.

Explain the term second ionisation energy

The energy required to remove one electron from each 1+ ion in one mole of gaseous 1+ ions to form one mole of 2+ gaseous ions.

Write an equation to represent the fourth ionisation energy of sodium

Na3+(g) -> Na4+(g) + e-

Explain the term successive ionisation energy

The energy required to remove each electron in turn from an atom/ion.

State and explain the general trend in successive ionisation energies as each electron is removed

Ionisation energy increases because as electrons are removed, the proton-to-electron ratio increases, ionic radius decreases, and nuclear attraction on remaining electrons increases.

Explain why the second ionisation energy of calcium is greater than the first ionisation energy of calcium

Ca+ is smaller than Ca, has a higher proton-to-electron ratio, and exerts a stronger nuclear attraction on the outer electron than neutral Ca.

State and explain the trend in first ionisation energy across a period

Increases across a period because nuclear charge increases while atomic radius decreases and shielding remains constant, leading to stronger nuclear attraction on outer electrons.

Explain why the first ionisation energy of C is greater than Li

C has a higher nuclear charge and smaller atomic radius with similar shielding, leading to stronger nuclear attraction on the outer electron.

Explain why the first ionisation energy of Be is greater than B

Be's outer electron is removed from a 2s subshell, whereas B's is in a higher-energy 2p subshell which is easier to remove.

Explain why the first ionisation energy of N is greater than O

N has singly-occupied 2p orbitals, whereas O has a paired electron in a 2p orbital; spin-pair repulsion in O makes its electron easier to remove.

Explain how successive ionisation energies show group number for element X

A large jump between 3rd and 4th ionisation energies indicates the 4th electron is removed from an inner shell closer to the nucleus with less shielding, meaning element X has 3 outer electrons (Group 3).