UNIT 2: SECTION 1 - PERIODICITY

Question 1

What property of atoms is affected across a period? How?

Answer 1

Atomic radius.
Number of protons increase, positive charge increases, electron shells pulled closer to the nucleus - atomic radius decreases.

Question 2

What physical property is linked to bond strength and structure across P3?

How?
Think about metallic bonding, macromolecules,
simple covalent molecules and IMF’s.

Answer 2

Na, Mg and Al all metals; metal-metal bonds get stronger across period due to:

• positive charge increase,
• delocalised electron number increasing,
• atomic radius decreasing.

Silicon - macromolecular and tetrahedral structure;

• Strong covalent bonds links all atoms together.
• A lot of energy needed to break these - high MP.

Phosphorous, Sulfur, Chlorine, molecular substances.
MP depends on LF strength; LF’s weak and easy to overcome - low MP’s.
Sulfur is S8; biggest molecule, higher MP than others.

Argon v.low MP because its monoatomic; very weak LF’s.