Physical Properties Of Period 3

Question 1

Atomic radius

Answer 1

Decreases across a period
More protons attracting electrons towards nucleus but shielding stays the same.

Question 2

First ionisation energy

Answer 2

Generally increases across a period
Decreases between magnesium and aluminium, as from group 2 to 3 electrons are in new sub shells, leads to small increase in shielding as s orbitals electrons repel the p orbitals.
Decreases between phosphorus and sulfur as from group 5 to 6 there is repulsion between paired electrons.

Question 3

Structure and bonding

Answer 3

Sodium, magnesium, aluminium form metallic bonds.
Silicon makes a giant covalent lattice.
Phosphorus, sulfur, chlorine form covalent bonds.

Question 4

Melting point of metals

Answer 4

Increases across period
Due to across period there is a higher charge so more delocalised electrons, so there is a higher electrostatic attraction and more energy needed to break the bonds.

Question 5

Melting point of molecules

Answer 5

Melting point depends on size of molecule, bigger molecule has higher melting point due to more van der waals.
Silicon is a macromolecule (giant) - very high melting point.
Sulfur forms an S8 molecule
Phosphorus forms a P4 molecule
Chlorine forms a Cl2 molecule