A Closer Look at Ionisation Energies

Question 1

Why does the first ionisation energy drop between Group 2 and 3?

Answer 1

The first ionisation energy drops because aluminium (Group 3) has its outer electrons in a higher electron orbital and further from the nucleus than the magnesium

Compared to Magnesium (Group 2) which has its outer electrons in a lower electron orbital. This means the electron is easier to remove from aluminium

Question 2

Which element has a lower first ionisation energy, magnesium (Group 2) or aluminium (Group 3)?

Answer 2

Aluminium has a lower first ionisation energy than magnesium because its outer electron is in a higher energy orbital, which is further from the nucleus and less tightly bound

Question 3

Why does the first ionisation energy drop between Group 5 (phosphorous) and Group 6 (sulfur)?

Answer 3

The ionisation energy drops because sulfur (Group 6) has a paired electron in its 3p orbital, which leads to increased electron - electron repulsion, making it easier to remove an electron compared to phosphorus, where the 3p electrons are unpaired

Question 4

What happens to successive ionisation energies when electrons are removed from an atom?

Answer 4

Each successive ionisation energy is higher than the previous because it becomes increasingly harder to remove electrons, due to the increasing positive charge of the ion and the decreasing repulsion between remaining electrons

Question 4

How can successive ionisation energies help determine an element’s group number in the Periodic Table?

Answer 4

The number of electrons that are relatively easy to remove corresponds to the group number. For example, in Group 2 elements, the first two electrons are relatively easy to remove - large jump in ionisation energy occurs after second electron is removed

Question 5

What can the sharp increase in ionisation energy between the first and second electrons indicate

Answer 5

The sharp increase indicates that the first electron is in the outermost shell, which is much easier to remove, while second electron is from a more tightly bound shell, leading to a significantly higher ionisation energy

Question 5

What do ionisationer energies of 906, 1763, 14 855, and 21 013 kJ mol-1 for the first five ionisation energies suggest about an element?

Answer 5

These values suggest that the element is in Group 2 of the Periodic Table because there is a large jump after the second electron is removed, indicating the transition from the outermost shell to a more tightly bound inner shell