Bond lengths are smaller when atoms form multiple bonds. Single overlap between two atoms forms a single covalent bond. So, when they overlap twice and thrice to form double and triple bonds the atoms to come closer to form a tight-knit. Such bonds are even harder to break. So, the bond length of a triple is smaller than a double and single bond.
The next factor affecting the bond length is the size of the atom involved. If the size of an atom shrinks, let’s say, from an orange to a lemon, then the distance between their nuclei decreases, decreasing their bond length. The opposite is true for bigger atoms. The large-sized atoms would have longer bond lengths. This change is evident when looking at the bond length of smaller-sized Fluorine F2 atoms at 142 pm and large-sized Iodine I2 atoms at 267 pm.
The crucial factor controlling the atom’s size is its electronegativity. The closer the electrons are to the nucleus of an atom, the more strongly they are pulled by the nucleus and decreasing its size.
The smaller size and stronger pull increase the electronegativity of an atom. And when such an atom is part of a covalent bond, the highly electronegative atom will pull its outer electrons, decreasing its size while also attracting the bond electrons and decreasing the bond length.
Last is the impact of s-orbitals in hybridization, known as the s-character. The s-character refers to the increased participation of the s-orbitals in the bond formation process. Since s-orbitals are closest to the nucleus, it tends to pull electrons closer. So greater involvement of the s-orbitals also shrinks the bond lengths as the bonds are also made of electrons.
The contribution of s-orbitals to the total is highest in the triple bonds (50%), followed by the double (33%) and single (25%).
So, more involvement of the s-orbitals leads to a shorter bond length.
- Pictorial representations and tables reinforce a concept. For such detailed explanation on the factors affecting the bond length, subscribe below.