Periodic Table

Question 1

Compare the decomposition temperature of magnesium carbonate, calcium carbonate and barium carbonate. Explain.

Answer 1

Decomposition temperature decreases from MgCO3 to BaCO3.

1. Ionic radius: Mg2+ < Ca2+ < Ba2+
2. Charge density and polarising power: Ba2+ < Ca2+ < Mg2+
3. Extent of polarisation of carbonate ion electron cloud and extent to which covalent bonds in carbonate anion are weakened: BaCO3 < CaCO3 < MgCO3
4. Energy required for decomposition: MgCO3 < CaCO3 < BaCO3

Question 2

When you’re asked to compare / state the trend of melting or boiling points, what should you be comparing?

Answer 2

The type of STRUCTURE (e.g. giant metallic structure for metals, giant molecular structure for silicon, and sms for covalent molecules) AND the type of BONDING (strong efoa between cations and sea of e-, strong&extensive covalent bonds, weak IMF between molecules).