Why do only valence electrons involve in bond formation?

Why do only valence electrons involve in bond formation ? Why not electron of inner shells ? Explain.

  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 outermost shell of an atom get affected.
  4. Thus electrons in valence shell are responsible for the formation of bond between atoms.