I just completed my Cambridge a levels with A* chemistry. While i did use save my exams to study i realized there was so much unwanted and so much missing. So i went through the syllabus and made my own notes that covers every topic and everything you need for an A*.
I have done 5 years of past pa...
GROUP 2
The Group 2 nitrates and carbonates become more thermally stable going down the
group
The charge density of the cation (Group 2 metal ion) and
the polarisation of the anion (the nitrate and carbonate ion) attribute towards this
increased stability
Trends in thermal stability going down the group
All Group 2 metals form 2+ ions as they lose two electrons from their valence shells
The metal cations at the top of the group are smaller in size than those at the
bottom
The metal cations at the top of Group 2, therefore, have the greatest charge
density as the same charge (2+) is packed into a smaller volume
As a result, smaller Group 2 ions have a greater polarising effect on neighbouring
negative ions
When a carbonate or nitrate ion approaches the cation, it becomes polarised
o This is because the metal cation draws the electrons in the carbonate or nitrate
ion towards itself
The more polarised the anion is, the less heat is required to thermally decompose
them
Therefore, the thermal stability increases down the group
o As down the group, the cation becomes larger
o Thus has a smaller charge density
o And a smaller polarising effect on the carbonate or nitrate anion
o So the anion is less polarised
o Therefore, more heat is required to thermally decompose them
Trends in Solubility & Enthalpy Change of Solution of
Group 2 Hydroxides & Sulfates
The solubility of Group 2 hydroxides increases down the group
In contrast, the Group 2 sulfates show a decrease in solubility going down the group
Compounds that have very low solubility are said to be sparingly soluble
Most of the sulfates are soluble in warm water with the exception of barium
sulfate which is insoluble
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