“The average distance between the centre of the nuclei of the two bonded atoms is called bond length”.
It is expressed in terms of Angstrom (1 Å = 10-10 m) or picometer (1pm = 10-12m).
In an ionic compound, the bond length is the sum of their ionic radii (d = y+ + y-) and in a covalent compound, it is the sum of their covalent radii (e.g., for HCl, d = yH + YC).
Factors affecting bond length
(i) The bond length increases with increase in the size of the atoms. For example, bond length of H-X are in the order, HI>HBr>HCl>HF.
(ii) The bond length decreases with the multiplicity of the bond. Thus, bond length of carbon–carbon bonds are in the order, C = C < C – C.
(iii) As an s-orbital is smaller in size, greater the s-character shorter is the hybrid orbital and hence shorter is the bond length.
For example, sp3 C-H>sP2sp C – Hsp3
(iv) Polar bond length is usually smaller than the theoretical non-polar bond length.