Why do metals in Group 1 get more reactive nearer the bottom of the Group?

Answer 1

The reactivity of an element largely depends on its electronic configuration. All the 1st group elements have one electron each in the outer most s-orbital. Their reactivity is due to the loss of this electron and formation of a uni positive ion. The ease with which the element loses the electron dictates its activity. As we go down the group, the distance between the outer most orbital and nucleus increases and hence the ease with which the element loses the electron increases as we go down the group. So naturally the reactivity increases.

However in the case of 7th group elements(halogens) the electronic configuration is s2p5. They acquire stability by acquiring another electron. This is called electron affinity. This increases as we go up a group. So we find the more reactive element at the top of the group.

We can generalize this like this. The reactivity of an element depends on the ease with which it acquires the nearest iner gas electronic configuration.

Answer 2

Group I metals only have one valence electron, as opposed to the two that Group II has. This means it takes less energy for the alkali metals to release their electron than for the alkaline earth metals to release their two.

Answer 3

They have one electron and only one shell. Atoms like having full electron shells and a full shell for Group 1A atoms is only 2 electrons so it only needs one electron to get happy. Any atom with 1 free electron can easily make this happen.