When comparing single, double, and triple covalent bonds formed between two atoms X and Y, decreasing the number of π bonds between the atoms will:decrease the overall bond dissociation energy and bond strength.increase the bond length.decrease the bond rigidity (allow more bond rotation).

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11ecba2d_1217_d932_a3bf_e9926e853c83_MD0008_00 Covalent bonds between atoms are formed by sharing electrons, which is made possible through overlap of the atomic orbitals from each atom. Covalent bonds made by the end-to-end overlap of orbitals are called sigma (σ) bonds, whereas covalent bonds made by the side-to-side overlap of p orbitals are called pi (π) bonds. Although some atoms participate only in single covalent bonding (by a σ bond), other atoms can participate in multiple bonds (double or triple bonds) by the addition of one or more π bonds. In this way, a double bond consists of one σ bond and one π bond, and a triple bond consists of one σ bond and two π bonds. Comparisons can be made between single, double, and triple covalent bonds provided that the bonds being compared involve the same two types of atoms. The overall dissociation energy of a bond (the energy required to break the bond) results from the sum of all σ and π bonding contributors. Therefore, the overall bond dissociation energy and bond strength tend to decrease (relative to a triple bond) as the number of π bonds decreases (Number I). Because of the shapes of the orbitals involved, bond length tends to increase (relative to a triple bond) as the number of π bonds decreases (Number II). Because σ bonds are made by an end-to-end orbital overlap, free rotation around the bond between the two σ-bonded atoms can be achieved while maintaining the orbital overlap. Therefore, decreasing the number of π bonds also decreases the rigidity of the bond between the atoms (Number III). Educational objective: Multiple covalent bonds formed by s and p orbitals consist of one σ bond (end-to-end orbital overlap) and one or more π bonds (side-to-side p orbital overlap). Decreasing the number of π bonds between two atoms increases bond length, decreases bond rigidity, and decreases the overall bond dissociation energy and strength.

When Comparing Single, Double, and Triple Covalent Bonds Formed Between