The thermal stability of the group II carbonates from magnesium to barium
- A. decreases down the group
- B. is the same for all
- C. increases down the group
- D. first increases then decreases
Explanation
A small, highly charged cation polarises the carbonate ion strongly and weakens the carbon to oxygen bonds, so magnesium carbonate decomposes at a relatively low temperature while barium carbonate needs a much higher one. Polarising power falls as the cation gets larger down the group, so stability rises. The nitrates and hydroxides follow the same pattern for the same reason.