Explain how the number of valence electrons in atoms relate to their bonding with other atoms to form molecules

valence electrons are the number of electrons in the outer shell. there can only be 8 electrons in the outer shell. The number of valence electrons can be used to determine how many bonds are needed.

For example: H2O

O (oxygen) has 6 valence electrons
H (hydrogen) has 1 valence electron

O needs 2 more electrons to be stable
H needs 1 more electron to be stable

O forms one bond with two H atoms to form H2O.