If you suspect a solution contains sulfate ions you can add a solution of barium chloride and if they are present an insoluble white precipitate will form which is barium sulfate.īecause of the insolubility of barium sulfate, and because barium is a heavy element capable of absorbing X-rays we can use it for a procedure known as a barium meal. The insolubility of barium sulfate is very useful as it can easily be used as a test for sulfate ions. Magnesium sulfate is readily soluble in water whereas barium sulfate is insoluble. Sulfates: As you go down the group the solubilities of the group 2 sulfates decrease. Magnesium hydroxide is virtually insoluble, whereas barium hydroxide will readily dissolve in water. Hydroxides: As you go down the group the solubilities of the group 2 hydroxides increase. This is because once again it is easier for the group 2 metal to be oxidised (lose an electron) because the outer shell electrons are further away from the nucleus and experience greater amounts of shielding. The hydrogen atoms originally in water are reduced from an oxidation state of +1 to an oxidation state of zero.Īs you go down the group the reactions become more vigorous.
The group 2 metal is oxidised from an oxidation state of zero to an oxidation state of +2. This is another example of a redox reaction. Metal + Water -> Metal Hydroxide + Hydrogen Group 2 elements all react with water in a similar way: However on closer examination of the crystal packing for each of the group 2 elements, this is a poor explanation at best, and as such it is best left as an interesting property of group 2. If you look at the graph you can see there is a small anomaly for Magnesium, for A-level courses you are not expected to explain this deviation in the trend, and some text books mention a possible reason for this ‘blip’ is a change in the crystal structure. As the atom gets larger there is now a smaller charge/volume ratio (they are becoming much larger (increase volume) but their charges remain the same (+2)) and the delocalised electrons are further away from the positive nucleus which means it takes much less energy to break this metallic bonding attraction. Melting points generally decrease down the group this is because they are all metals and hence have metallic bonding which consists positive metal ions surrounded by a sea of delocalised electrons. This is because, as explained previously, it is much easier to remove an outer shell electron as you go further down the group (lower ionisation energies). The reactivity of the group 2 elements increase as you go down the group.
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