Question

why do some elements and compounds react vigorously while others are inert

Answer 1

because of valence electron in its outermost shell

Answer 2

The reason why some elements reacts and some are inert is given below:

Every element present or found in this world always wants to acquire a stable electronic configuration. So, because of the outermost electrons present, they may loose one electron or may also gain electron to achieve stable configuration like those of noble gas. And therefore, some elements like sodium, potassium, etc reacts vigorously. For example, Sodium has the electronic configuration as 2,8,1

So, if sodium loss the outermost one electron, then it will be able acquire the stable configuration of 2,8

Therefore, to acquire and octet or a stable configuration the elements reacts vigorously.

On the other hand, some elements like helium, nitrogen, neon, argon, are inert because they have already a stable configuration and have completely filled valence shells. So, they do not have tendency to loose or take extra electron into it and hence they are inert.

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