The electrons in the valence shell of an atom in a molecule may not be shared. A nonbonding valence electron pair is termed a lone pair.
Lone pairs fashion a high electron density in their region of orbital space. So, even though they are not bonded, lone pairs influence the shape of a molecule.
In bonding, shared electrons are concentrated between 2 atoms. Lone pairs, without the attention of a 2nd atom, are cozy homebodies: typically located a bit closer to the atomic nucleus than bonding pairs.
Lone pairs often exhibit a negative polar character. As electron regions repel each other, a lone pair nudges its brethren bonding pair away, reducing molecular bond angle.