Chapter 7 - Ionisation Energies

Question 1

State 3 factors affecting ionisation energy

Answer 1

Atomic radius
Nuclear charge
Electron shielding

Question 2

Explain how atomic radius affects ionisation energy

Answer 2

The greater the distance between the nucleus and the the outer electrons in the highest energy shell, the less the nuclear attraction

Question 3

Explain how nuclear charge affects ionisation energy

Answer 3

The more protons there are in the nucleus of an atom, the greater the nuclear attraction the outer electrons experience

Question 4

Explain how electron shielding affects ionisation energy

Answer 4

The inner shell electrons repel the outer electron due to both being negatively charged. This shielding effect reduces the attraction between the nucleus and the outer electrons

Question 5

State the definition of the second ionisation energy

Answer 5

The 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+ ion

Question 6

What does a large jump in successive ionisation energies mean?

Answer 6

The electron is being removed from a different shell

Question 7

What do successive ionisation energies allow prediction to be made about?

Answer 7

The number of electrons in the outer shell
The group of the element in the periodic table
The identity of an element

Question 8

State the two key patterns in the first ionisation energies in the periodic table

Answer 8

1. A general increase in first ionisation energy across a period
2. A sharp decrease in first ionisation energy between the end of one period and the start of the next period

Question 9

What is the trend in the first ionisation energy going down a group?

Answer 9

Decreases

Question 10

Explain why the first ionisation energies decrease down a group (in terms of atomic radius, electron shielding and nuclear charge).

Answer 10

• Although nuclear charge increases
• the effect is outweighed by the atomic radius increasing
• there are also more inner shells so shielding increases
• so the nuclear attraction on outer electrons decreases
• therefore the first ionisation energy decreases

Question 11

What is the trend in the first ionisation energy going across a period?

Answer 11

Increases

Question 12

Explain the general trend in the first ionisation energy going across a period (in terms of shielding, nuclear charge and atomic radius)

Answer 12

-The nuclear charge increases (more protons to electrons)
- There is similar shielding (same number of shells) so it has little effect on ionisation energy
- as nuclear attraction increases, the atomic radius decreases
- resulting in the first ionisation energy increasing

Question 13

Why is ionisation energy lower for boron than for beryllium?

Answer 13

The 2p sub shell is beginning to be filled in boron. The 2p sub shell has a higher energy (energy increases as shell number increases) than the 2s sub shell in beryllium. Therefore it is easier to remove the 2p electron in boron

Question 14

Explain why there is a fall in the first ionisation energy from nitrogen to oxygen

Answer 14

The electrons begin to pair in the p-orbitals of the 2p sub shell. The repulsion between one of the paired electrons in oxygen means it is easier to remove the electron from the oxygen atom