Ionisation Energies

Question 1

What is the first ionisation energy?

Answer 1

The energy needed to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions.

Question 2

How does ionisation energy change going down a group (e.g., Group 2)?

Answer 2

Ionisation energy decreases down a group. This is due to increased shielding and larger atomic radius, meaning the outer electrons are further from the nucleus and less strongly attracted.

Question 3

How does ionisation energy change across a period (e.g., Period 3)?

Answer 3

Ionisation energy generally increases across a period. Atomic radius decreases, and the effective nuclear charge increases, leading to stronger attraction of electrons to the nucleus.

Question 4

What three factors influence ionisation energy?

Answer 4

Atomic radius, nuclear charge, and shielding effect.

Question 5

Why is the first ionisation energy of Beryllium (Be) higher than Boron (B)?{[(Exception to Period Trend (Beryllium)]}

Answer 5

Beryllium’s 2s electrons are in a lower energy level and more tightly bound than Boron’s 2p electrons.

Question 6

Why is the first ionisation energy of Nitrogen (N) higher than Oxygen (O)?{[(Exception to Period Trend (Nitrogen)]}

Answer 6

Nitrogen’s p-orbitals are half-filled and more stable, requiring more energy to remove an electron compared to Oxygen.

Question 7

What is the shielding effect?

Answer 7

The reduction in the attractive force between the nucleus and the outer electrons due to the presence of inner electrons that block the nuclear charge.

Question 8

What is the second ionisation energy?

Answer 8

The energy required to remove a second electron from a 1+ ion.