8 - Periodicity

Question 1

Give the four blocks elements are classified as.

Answer 1

• s
• p
• d
• f

Question 2

Describe and explain the trend in atomic radii across a group?

Answer 2

1. Increased nuclear charge
2. Increased electrostatic attraction
3. Similar shielding
4. Decrease across group left to right

Question 3

Describe and explain the trend in first ionisation energy across Group 3. (6)

Answer 3

1. General increase left to right
2. Due to increasing number of protons and electrostatic attraction
3. Small drop Mg to Al
4. As electrons in Al are in 3p rather than Mg’s 3s, so are easier to remove as they are higher in energy
5. Small drop P to S
6. Sulfur has a paired electron in 3p, which Phosphorus does not. So there is eadditional repulsiion which makes it easier to remove an electron

Question 4

Describe the melting and boiling points of Period 3.

Answer 4

• Na, Mg and Al have strong metallic bonding
• This increases across the number of delocalised electrons increases
• Si is macromolecular so has many strong covalent bonds
• Cl2, S8, P4 are simple molecularso have only weak van der Waals
• S8 > P4 > Cl2 as it has more electrons, so more van der Waals
• Ar contains weak van der Waals as it is monoatomic.

Question 5

What formula does Phosphorus (V) oxide have?

Answer 5

P4O10