Why do valency electrons involve in bond formation , than electrons of inner shells ?

Explanation

1) When two atoms come sufficiently close together the valence electrons of each atom experience the attractive force of the nucleus in the other atom .
2) The nucleus and the electrons in the inner shell remain unaffected when atoms come close together .
3) The electrons in outer most shell of an atom get affected .
4) Thus electrons in valence shell are responsible for the formation of bond between atoms .