Periodic trends

Question 1

Electronegativity

Answer 1

Tendency for an atom to attract a shared electron pair in a covalent bond

Question 2

Why does electronegativity increase across a period?

Answer 2

Nuclear charge increases across a period

Question 3

First ionisation energy

Answer 3

Energy required to remove one mole of electrons from one mole of atoms/ions in the gaseous state

Question 4

Explain the general increase in first ionisation energy as you move across a period

Answer 4

Nuclear charge increases across a period. More energy absorbed due to the stronger attractive force between valence electron and nucleus

Question 5

Two anomalies in first ionisation energy for period 2?

Answer 5

Boron and oxygen

Question 6

Two anomalies in first ionisation energy for period 3?

Answer 6

Aluminium and sulphur

Question 7

Why is the ionisation energy of boron lower than that of beryllium?

Answer 7

Boron has its valence electron in the p sub-level and beryllium in the s sub-level.

The p sub-level is higher in energy and further away,

so weaker attractive force from the positive nucleus.

Hint: write their electron configurations

Question 8

Why does oxygen have a lower ionisation energy than nitrogen?

Answer 8

Nitrogen has singly filled p orbitals, so less repulsion.

In oxygen, one of the electrons in a doubly filled orbital is removed and there is more repulsion