Physical properties of period 3 elements

Question 1

What happens to atomic radius across period 3?

Answer 1

Decreases

Question 2

What happens to first ionisation energy across period 3?

Answer 2

Increases, except it decreases between:
- Mg to Al: electrons in a new sub-shell with increased shielding so less energy required to remove them
- P to S: repulsion between electrons in same orbital, so less energy required to remove them

Question 3

Structure and bonding of Si?

Answer 3

Metalloid, forms giant covalent lattice

Question 4

Structure and bonding of Argon?

Answer 4

Noble gas - doesn’t form bonds

Question 5

What happens to melting point of metals across period 3?

Answer 5

Increases due to higher metal charged cations and more delocalised electrons (stronger electrostatic attraction, so stronger metallic bonding)

Question 6

What molecules do the non-metals in period 3 form?

Answer 6

Si - macromolecule
P - P4
S - S8
Cl - Cl2

Question 7

What happens to melting point of non-metals across period 3?

Answer 7

Si - giant covalent lattice with strong covalent bonds, so very high melting point

Others depend on strength of van der Waals forces (in relation to their size)

Si > S > P > Cl > Ar