3.1.2 Group 2

Explain that Group 2 elements have a S2 electron configuration and the loss of these electrons in redox reactions forms 2+ ions

Group 2 elements all have two electrons in their outer shell (s2). They can lose their two outer electrons to form 2+ ions. Their ions then have every atom's dream electronic structure - that of a noble gas.

Explain the uses of some Group 2 compounds as bases, including equations, for example (but not limited to): i) Ca(OH)2 in agriculture to neutralise acid soils ii) Mg(OH)2 and CaCO3 as 'antacids' in treating indigestion

Group 2 elements are known as the alkaline earth metals, and many of their common compounds are used for neutralising acids. Here are a couple of common examples. (i) Calcium hydroxide (slaked lime, Ca(OH)2) is used in agriculture to neutralise acid soils. It has to be used in moderation though, otherwise the soils will become too alkaline to support crop growth. (ii) Magnesium hydroxide (Mg(OH)2) and calcium carbonate (CaCO3) are used in some indigestion tablets as antacids - these neutralise excess stomach acid. In both cases, the ionic equation for the neutralisation is: H+(aq) + OH-(aq) -> H2O(l)

Explain the trend in reactivity of Group 2 elements down the group in terms of the first and second ionisation energies down a group

When Group 2 elements react they lose electrons, forming positive ions (cations). The easier it is to lose electrons (i.e. the lower the first and second ionisation energies), the more reactive the element. So because ionisation energy decreases down the group, reactivity increases down the group.

Describe the relative reactivities of Group 2 elements Mg -> Ba as shown by their redox reactions with: i) oxygen ii) water iii) dilute acids

i) When Group 2 metals burn with oxygen, you get solid white oxides. The oxides of the Group 2 metals react readily with water to form metal hydroxides, which dissolve. The hydroxide ions, OH-, make these solutions strongly alkaline (e.g. pH 12-13). Magnesium oxide is an exception - it only reacts slowly and the hydroxide isn't very soluble. The oxides form more strongly alkaline solutions as you go down the group, because the hydroxides get more soluble. ii) The Group 2 metals react with water to give a metal hydroxide and hydrogen. The metal hydroxide that forms dissolves in water to produce hydroxide ions (OH-). These make the solutions strongly alkaline, with a pH of about 12-13. The elements react more readily down the group because the ionisation energies decrease. This is due to the increasing shielding effect. iii) When Group 2 metals react with dilute hydrochloric acid, you get a metal chloride and hydrogen. Here's the general equation for the reaction of a Group 2 metal (M) with dilute hydrochloric acid. Different acids will produce different salts. For example, if you use dilute sulphuric acid, you'll get a metal sulphate.