Question

Explain the following:
Why do alkali metals not form di-positive ions?

Answer 1

Hint : For an element to become a di-positive ion it should have a minimum two valence electrons in its valence shell to acquire $ + 2 $ charge. Take the electronic configuration of alkali metals into consideration and see if they can lose two electrons or not.

Complete step by step solution
First let us see what do-positive ions are. The ‘di’ in di-positive stands for two. We know when an atom loses an electron it gains a positive charge. So when an atom loses two electrons it gains two positive charges and thus it is called a di-positive ion. The electron gains a single positive charge known as mono-positive ions. Examples of di-positive ions are $ M{g^{ + 2}},C{a^{ + 2}} $ .
We know alkali metals have a general electronic configuration is [noble gas] $ n{s^1} $ . They all have one electron in their valence shell. So they can lose only one electron to attain stable electronic configuration. So they acquire a single positive charge. That is why they are mono-positive and cannot be di-positive. They acquire only $ + 1 $ charge for example $ L{i^{ + 1}},N{a^{ + 1}},{K^{ + 1}},R{b^{ + 1}} $ .
So we can say alkali metals cannot form di-positive ions because of its electronic configuration it has only one electron in its valence shell. Also a great amount of energy will be required to remove the second electron for di-positivity because that electron is in stable electronic configuration.

Note
Alkaline earth metals are known to form di-positive ions vastly because they have two electrons in their valence shell. Because of this fact alkaline earth metals are less reactive and much harder than alkali metals. Some elements are known to form more than one type of positive ion. For example iron can form di-positive and tri-positive ions.