Ionisation Energy

Ionisation energy

Te energy required to remove a mole of electrons from a mole of atoms in the gaseous state

Second ionisation energy

The energy required to remove the second electron

First ionisation energy equation for sodium

Na+ (g) —> Na+ (g) + e-

Second ionisation energy equation for sodium

Na+ (g) —> Na2+ (g) + e-

Third ionisation energy equation for sodium

Na2+ (g) —> Na3+ (g) + e-

Three factors that affect ionisation energy

Distance from nucleus, nuclear charge, shielding and spin pair repulsion

Distance from nucleus

Smaller atoms have a higher attraction between positive nucleus and negative electrons so a higher ionisation energy

Nuclear charge

Higher positive nucleus charge = stronger attraction to electrons so ionisation energy increases

Shielding

Repulsion by electrons in inner shells between the nucleus and outer shell decreases ionisation energy

Spin pair repulsion

A pair of electrons in the same orbital repel eachother

High first ionisation energy

Smaller atoms, less shielding, more protons

Trends in ionisation energies

Show periodicity (a trend across a period of the Periodic Table). Group 1 metals have a low ionisation energy, noble gases have a very high ionisation energy

Across a period

Ionisation energy increases

Across a period for nuclear charge

Nuclear charge increases, causes the atomic radius of the atoms to decrease, the outer shell is closer to the nucleus and the distance between the nucleus decreases

Across a period for shielding

The shielding between inner electrons remain constant, electrons are added on the same shell. Becomes harder to remove, more energy is needed

From one period to the next

Large decrease in ionisation energy between the last element and first element in the next period. There is increased distance between the nucleus and outer electrons since another shell is added. Increased shielding

Ionisation energy down a group

Ionisation energy decreases

Ionisation down a group

The number of protons increases, the nuclear charge increases. The atomic radius of the atoms increases, more shells are added. The distance between the nucleus and outer electron increases. Shielding increases. The factors outweigh the increased nuclear charge, becomes easier to remove the outer electron as you go down the group