2.1 Periodicty

Question 1

What is the general trend in atomic radius across period 3 and why?

Answer 1

• Decreases
• Nuclear charge increases so there’s a greater attraction of electrons towards the nucleus
• Amount of shielding stays the sae

Question 2

Explain why aluminium has a lower first ionisation energy that magnesium?

Answer 2

• First electron removed from Mg is in 3s sub shell
• First electron removed from Al is in a 3p sub shell
• 3s sub shell is lower energy that 3p

Question 3

Why does Sulphur have a lower first ionisation energy than Phosphorus?

Answer 3

• First electron from P is removed from 3p sub shell and is unpaired
• First electron removed from S is removed from a 3p sub shell but is paired
• Sulphur has a lower ionisation due to electron pair repulsion

Question 4

Describe melting and boiling point across period 3.
- Na to Mg to Al
- Si
- P, S, Cl and Ar

Answer 4

• Increase because strength f metallic bonds increase. Na+, Mg2+, Al3+. Na is the smallest ion so weaker metallic bonds.
• Si has highest melting point. Macromolecular structure held by strong covalent bonds which require a lot of energy to break
• Simple molecular molecules. Sulfur is biggest and has strongest IDD, so higher melting and boiling point. Cl is the smallest and has weakest IDD so lwest meting and boiling point. Ar only exists as atom so has leaked IDD so lowest melting and boiling point