Periodicity

Question 1

Describe and explain the trends in melting and boiling points across period 3

Answer 1

Increases between Na- Al - no. delocalised electrons increase, greater attraction b/w cations & electrons so ++ energy required- metallic bonding is an infinite lattice of cations held by a sea of delocalised electrons

Increases to Si, as = giant covalent structure- big lattice w/ covalent bonds which require a lot of energy

Decreases to Phosphorus as simple molecular, molecules held together by weak Van der Waals. Increases to Sulphur as sulphur is a larger molecule (S8 compared to P4), so larger Van der Waals. Decreases from Phosphorus to Argon as smaller molecule, same bonding

Question 2

State the type of structure shown by a crystal of silicon. Explain why the melting point of S is very high.

Answer 2

Giant covalent molecule/macromolecular structure

Strong covalent bond

Question 3

Generally there is an increase in 1st ionisation energy across period 3. However, between Mg and Al it decreases. Explain why

Answer 3

Mg is in the S orbital but Al is in the p block, where there is slightly greater shielding

Question 4

Generally there is an increase in 1st ionisation energy across period 3. However, between P and S it decreases. Explain why

Answer 4

S has a lower ionisation energy because the electrons start doubling up in the orbitals, therefore there is some repulsion

Question 5

Describe and explain the trends in 1st ionisation energy across period 3

Answer 5

Generally increases but ‘jagged line’ (decrease b/w Mg and Al, and P and S)
Nuclear charge increases but similar shielding
Therefore needs higher energy level

Question 6

Why is there not an atomic radius value for Argon?

Answer 6

Often values are obtained by reacting them w/ others and working out distance b/w 2 nuclei
Argon doesn’t react therefore can’t work out

Question 7

Describe and explain the trends in atomic radius across period 3.

Answer 7

Generally decreases (Na --> Cl)
Stronger nuclear charge across the period
Therefore stronger attraction b/wn nuclear and outer electrons --> pulls closer

Question 8

Give the electron configuration of Silicon 14

Answer 8

1s2 2s2 2p6 3s2 3p2