7.2 Ionisation Energy

Question 1

What is first ionisation energy?

Answer 1

Energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions

Question 2

First ionisation equation in Sodium

Answer 2

Na (g) ——> Na+ (g) + e-

Question 3

Second ionisation equation for Sodium

Answer 3

Na+ (g) ——> Na 2+ (g) + e-

Question 4

First ionisation equation of Chlorine

Answer 4

Cl (g) ——> Cl+ (g) + e-

Question 5

Factors affecting ionisation energy

Answer 5

Atomic radius
Nuclear charge
Electron shielding

Question 6

How does atomic radius affect ionisation energy?

Answer 6

Greater the distance between nucleus and outer electrons, less nuclear attraction
Less attraction means lower ionisation energy

Question 7

How does nuclear charge affect ionisation energy?

Answer 7

More protons in a nucleus of an atom, greater the attraction between nucleus and outer electrons
Greater attraction means higher ionisation energy

Question 8

How does electron shielding affect ionisation energy?

Answer 8

Electrons are negatively charged and inner shell electrons repel outer shell electrons
This repulsion is the shielding effect
Reduces attraction between nucleus and outer electrons - lower ionisation energy

Question 9

Why are successive ionisation energies higher?

Answer 9

After the first electron is lost, the other electrons are attracted more strongly to the nucleus
More ionisation energy is required to remove the other electrons

Question 10

What is second ionisation energy?

Answer 10

Energy required to remove one electron from each ion in one mole of gaseous 1+ ions of an element to form one mole of gaseous 2+ ions

Question 11

What happens to ionisation energy if shell changes?

Answer 11

Large increase in ionisation energy

The shell is closer to the nucleus, and there is less shielding, so greater ionisation energy

Question 12

What happens to ionisation energy across a period?

Answer 12

It increases, due to increasing nuclear charge

Question 13

What happens to ionisation energy down a group?

Answer 13

It decreases, due to increasing atomic radius

Question 14

Why does Boron have a lower ionisation energy than Beryllium?

Answer 14

Boron has no electrons in the 2p sub shell, but Beryllium has an electron in the 2p sub shell, which is further away from the nucleus, so less energy is released.

Question 15

Why does Oxygen have a lower ionisation energy than Nitrogen?

Answer 15

In Oxygen, there is a paired orbital in the 2p sub shell, so there is repulsion from the other electron, which means it’s easier to remove the electron, than in Nitrogen