Bond Length

“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.

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