Question

An atom that has only one electron in its valence electron shell is ______ chemically reactive?

Answer 1

Electron shell is the out side part of the atom 

Answer 2

The valence electrons are the electrons in the outermost electron shell of an atom.

Explanation:

The number of electrons in an atom's outermost valence shell governs its bondingbehaviour.

That is why elements whose atoms have the same number of valence electrons are grouped together in the Periodic Table.

Generally, elements in Groups 1, 2, and 13 to 17 tend to react to form a closed shell, corresponding to the electron configuration s2p6.

This tendency is called the octet rule, because the bonded atoms have eight valence electrons.