The reactivity of of group 2 increases as you go down, and the first ionisation energy decreases down to Barium, because of the increased atomic size and more shielding. However, the first ionisation energy of radium is slightly higher than barium, 509 kJ/mol compared to 502. Is this because the nucleus of radium is so much larger so counteracts the effect of another full shell of electrons?
Also, what chemical and physical properties of Group 2 do we have to know?
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Interesting question, Vicky. If you look at the Periodic Table, the elements in between Ba and Ra also include the first row of the f block (which is the one that seems to appear separately to the rest of the Periodic Table, right at the bottom). f electrons are less effective at shielding than d electrons. So, although Ra contains extra electrons that you would expect to increase shielding, they don't increase it by as much as the d electrons. But the nuclear charge of Ra has increased, so these 2 things combined lead to a slightly higher ionisation energy of Ra compared to Ba. Does that make sense? You don't need to know this for A-level!
In terms of physical and chemical properties of Group 2...
The physical properties are not specified in the syllabus but I would make sure that you can explain the trends in:
- melting and boiling points
- electronegativity
- atomic radius
- first ionisation energy
In terms of chemical properties, you need to be able to explain:
- the trend in reactivity
- the trend in solubility of the hydroxides
- the reactions of elements with oxygen and water
- the reactions of the oxides with water
- the thermal decomposition of the carbonates
Hope this helps!
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