7.2 - Ionisation Energies

Question 1

Define 1st ionisation energy

Answer 1

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

Question 2

State the factors that affect ionisation energies.

Answer 2

Atomic Radius
Nuclear Charge
Electron Shielding

Question 3

Explain how atomic radius affects ionisation energy.

Answer 3

Greater distance from nucleus to outer shell electrons lowers the force of attraction.

Question 4

Explain how nuclear charge affects ionisation energy.

Answer 4

The more protons there are in the nucleus, the greater the attraction between the nucleus and outer shell electrons.

Question 5

Explain how electron shielding affects ionisation energy.

Answer 5

Shielding effect: Repulsion between electrons in different inner shells repelling outer shells.
Shielding reduces the net attractive forces between nucleus and outer shell electrons.

Question 6

Why are successive ionisation energies higher than prior ones?

Answer 6

Once an electron is removed, per electron there is more nuclear attraction as the ratio of proton:electron increases, and the atomic radius (if the successive ionisation is the next shell) is smaller, increasing ionisation energy.

Question 7

Define second ionisation energy.

Answer 7

Energy required to remove one mole of electrons from one mole of gaseous 1+ ions to form 1 mole of 2+ gaseous ions.

Question 8

What can successive ionisation energies give you information about?

Answer 8

No. of electrons in the outer shell
Group of element in periodic table
Identity of element

Question 9

What are the trends of first ionisation energies?

Answer 9

General increase in ionisation energy across a period

Sharp decrease in ionisation energy from end of first period to beginning of next

Question 10

What are the 1st ionisation energy trends down a group?

Answer 10

First ionisation energy decreases due to increase in atomic radius - (more electrons per element in inner shells increasing shielding effect)
- Outer electron ends up being further from the nucleus lowering attraction

Question 11

What are the 1st ionisation energy trends across a period?

Answer 11

General increase in 1st ionisation energy (Periods 1-3)

• Increase in nuclear charge due to increase in atomic number.
• Shielding effect remains the same, nuclear attraction increases, atomic radius decreases. 1st ionisation energy increases.

Question 12

During period 2 there are drops in ionisation energies between Berylium and Boron, and Nitrogen and Oxygen. Explain why

Answer 12

Boron marks the start of 2p electron filling

• 2s sub shell is filled for Be
• 2p electron in Boron has higher energy than Berylium and is easier to remove.

Oxygen marks the beginning of 2p electron pairing

• In both N & O, the highest energy electron is the 2p sub shell
• There is a 2px2 in O and only 2px1 in N, the 2 electrons in 2px repel one another making it easier to remove lowering the ionisation energy.