Solid carbon dioxide, CO2, is similar to solid iodine, I2, in its structure and properties. Carbon is in Group 14. Silica, SiO2, is a Group 14 compound.

Question 8 [Chemical Bonding >3.2 Covalent bonding and co-ordinate (dative covalent) bonding including shapes of simple molecules]

Solid carbon dioxide, CO2, is similar to solid iodine, I2, in its structure and properties. Carbon is in Group 14. Silica, SiO2, is a Group 14 compound.

Which statement about solid CO2 and solid SiO2 is correct?

A Both solids exist in a lattice structure.

B Both solids have a simple molecular structure.

C Both solids have atoms joined by single covalent bonds.

D Both solids change spontaneously to gas at s.t.p.

Reference: Past Exam Paper – Chemistry (9701) March 2016 Paper 12 Q8

Solution:

     Answer: A

     Option A:  “It should be known that solid I₂ has a simple molecular lattice, therefore it can be deduced from the information in the question that solid CO₂ does too”

     Option B can be discredited since we know that SiO₂ has a similar structure to diamond, i.e, a giant covalent structure, not simple molecular.

    Option C can be eliminated. While SiO₂ has four single bonds, CO₂ has two double bonds and is linear rather than tetrahedral like SiO₂.

    Option D can be eliminated since at stp, SiO₂ is a solid and will not change spontaneously (naturally) into a gas.