Chapter 8

Question 1

What is periodicity?

Answer 1

Repeating trends in properties of elements across periods in the periodic table.

Question 2

Describe the trend in atomic radius across Period 3.

Answer 2

Atomic radius decreases due to increasing nuclear charge pulling electrons closer.

Question 3

Describe the trend in first ionisation energy across Period 3.

Answer 3

Generally increases due to increasing nuclear charge, with exceptions at Mg-Al and P-S due to electron configurations.

Question 4

Why does ionisation energy drop from Mg to Al?

Answer 4

Al’s electron is in 3p orbital, higher energy and more shielded than Mg’s 3s electron.

Question 5

Explain the drop in ionisation energy from P to S.

Answer 5

Sulfur has paired electrons causing repulsion and easier ionisation.

Question 6

Describe the trend in melting points across Period 3.

Answer 6

Melting point increases from Na to Si due to metallic and giant covalent bonding, then drops at P, S, Cl and Ar due to molecular and atomic structures.

Question 7

Explain the structure of sodium in Period 3.

Answer 7

Metallic lattice with delocalised electrons.

Question 8

Why does silicon have a high melting point?

Answer 8

Giant covalent lattice with strong covalent bonds.

Question 9

Why do chlorine and argon have low melting points?

Answer 9

Simple molecular and atomic structures with weak Van der Waals forces.

Question 10

Explain the trend in electrical conductivity across Period 3.

Answer 10

Conductivity decreases from metals (Na, Mg, Al) to non-metals due to lack of free electrons.