A smaller or more highly charged cation polarises the anion more strongly, weakens its internal bonds and lowers the decomposition temperature or stability.
Magnesium ethanedioate ( MgC2O4 ) decomposes on gentle heating to form magnesium carbonate and carbon monoxide.
Magnesium carbonate undergoes thermal decomposition at a higher temperature than magnesium ethanedioate.
Explain the trend in the thermal decomposition of Group 2 carbonates going down the group.
An answer that makes reference to the following points:
- the temperature of decomposition of carbonates / thermal stability increases (down the group)
- the size of the cation increases (but has the same charge)
- (so) polarises the anion / carbonate (ion) less
(1)
Ignore references to rate Ignore "decomposition decreases down the group"
Allow amount of heat energy needed to decompose increases down the group
Accept reference to the metal ion size/radius Allow charge density of (cat)ion decreases Ignore "ion size decreases"
Do not award atomic radius
(3)