Bond length is the distance between centers of atoms bonded within a molecule. bond length is measured in units of picometers (pm) which is equal to 10^-12 meters. Bond length depends on three main factors.
- Size of atoms: smaller atoms have lower bond length. The lowest bond length is between two atoms of the hydrogen, which has the smallest atom size. The bond length of H-H bond is 74 pm.
- Bond strength: stronger bonds tend to have lower bond length as compared to weaker bonds.
- Multiplicity of bonds: Multiply bonds tend to have lower bond lengths as compared to single ply bonds
a) Size of atoms – Bond length increases with the increase in size of the
atoms e.g. bond length between H & Cl in HCl = 127 pm whereas bond
length between C & Cl, C — Cl = 177 pm.
b) Nature of bonds – Bond length decreases with the multiplicity of
bonds because attractive forces between electrons and nuclei will
increase with the increase in number of shared electrons between
bonded atoms e.g. in C — C , bond length is 154 pm whereas in C ═ C
bond length is 134 pm.
3) Bond angle – As we know that the molecules formed by covalent bond are
oriented in a specific direction. As a result the atoms of these molecules
develop a bond angle.
The bond angle is defined as the average angle between the orbitals
containing bonding electron pairs around the central atom in a molecule. It is
expressed in degree / minute / second. It helps in determining the shape of
the molecules because it gives an idea about the distribution of orbitals
around the central atom in a molecule.