Bonded atoms are constantly in motion. Repulsive forces push them apart and attractive forces pull them back together. A bond length is defined as the equilibrium distance between bonded atoms. At the bond length distance the attractive forces and repulsive forces cancel each other out and the net force acting on the atoms is zero. Bond length is related to bond energy.

Bond Lengths (pm) for Selected Covalent Bonds

	H	C	N	O	S	F	Cl	Br	I
H	74	109	101	96		92	127	141	161			CC	154
C		154	147	143	182	135	177	194	214			CC	134
N												CC	120
O												OO	148
S												OO	121
F						142						NN	145
Cl							199					NN	110
Br								228
I									267