Ions & Ionisation energy

Question 1

What is an ion?

Answer 1

An ion is a charged atom. It is formed when electrons are gained/lost.

Question 2

What does ionisation energy measure?

Answer 2

Ionisation energy measures the ease with which electrons are lost in the formation of positive ions.

Question 3

Define first ionisation energy

Answer 3

The first ionisation energy of an element is the energy required to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.

Question 4

What are the factors affecting ionisation energy?

Answer 4

• Atomic radius
• Nuclear charge
• Electron shielding

Question 5

How does atomic radius affect ionisation energy?

Answer 5

The greater the distance between the nucleus and the outer electrons, the less attractive the force.

Question 6

How does nuclear charge affect ionisation energy?

Answer 6

The greater the number of protons in the nucleus, the greater the attractive force.

Question 7

How does electron shielding affect ionisation energy?

Answer 7

The outer shell electrons are repelled by any inner shells between the electrons and the nucleus. This repelling effect reduces the overall attractive force experienced by the outer electrons.

Question 8

Describe the trend in ionisation energies across a period

Answer 8

General increase across a period - due to increase in nuclear charge across period.

Question 9

Describe the trend in ionisation energies down a group

Answer 9

Decrease down a group - due to presence of extra shells down a group.

Question 10

Why does boron have a lower first ionisation energy than beryllium?

Answer 10

Boron’s outermost electron is in the 2p subshell instead of the 2s subshell. This means it has higher energy level and it is easier to remove.

Question 11

Why does oxygen have a lower first ionisation energy than nitrogen?

Answer 11

Oxygen has a 2p orbital with an electron pair. The electron is easier to remove because of electron repulsion.