Ionisation Energies

Question 1

What is ionisation energy?

Answer 1

The energy required to remove 1 mol of electrons from 1 mol of GASEOUS atoms

Question 2

What are the axises on ionisation energy graphs?

Answer 2

Ionisation no on x
Ionisation energy kJmol-1

Question 3

How do ionisation energies show evidence for shells?

Answer 3

Each energy is larger than the one before because electrons are removed from closer to the nucleus and so have greater attraction from +ve nucleus. As each is removed there is less repulsion between electrons and each shell is drawn closer to the nucleus.

Question 4

Write half equations for ionisation of Li

Answer 4

Li (g) -> Li+ (g) + e-
Li+(g) -> Li2+(g) + e-
Li2+(g) -> Li3+(g) + e-

Element must be gas!!

Question 5

How does atomic radius affect IE?

Answer 5

Greater the atomic radius, the weaker the nuclear attraction experienced by outer shell electrons

Question 6

How does nuclear charge effect IE?

Answer 6

The greater the nuclear charge (protons in nucleus) the stronger the attractive force experienced by outer electrons

Question 7

How does electron shielding impact IE?

Answer 7

Repulsion between electrons in different inner shells. Inner shell electrons repel outer shell electrons. The more inner shells the greater the shielding force and the less force experienced by outer electron. Shielding reduces NET ATTRACTIVE FORCE from +ve nucleus

Question 8

How do IE indicate different shells?

Answer 8

There is a large jump in IE between the 5th and 6th ionisations, indicating that the 6th electron is removed from a shell closer to the nucleus

Question 9

Explain why each ionisation energy is greater than previous

Answer 9

• less repulsion among remaining electrons
• electrons drawn in more tightly to the nucleus
• greater nuclear attraction so each successive electron requires more energy to be removed