Why the Bond Energy of N≡N Triple Bond Exceeds That of C≡C Triple Bond

The bond energy of the Nitrogen-Nitrogen (N≡N) triple bond is higher than that of the Carbon-Carbon (C≡C) triple bond due to several factors. This difference in bond energy can be understood through the interactions involving atomic size, orbital overlap, electronegativity, and stability.

Atomic Size and Orbital Overlap

Nitrogen atoms are smaller than carbon atoms. This difference in size allows for better overlap of their p orbitals when forming a triple bond. The enhanced overlap leads to stronger bonding interactions in N≡N compared to C≡C. The π bonding in N≡N is more stable due to the smaller size and therefore more effective overlap of the p orbitals.

Bond Composition

The N≡N bond consists of one sigma (σ) bond and two pi (π) bonds, similar to the C≡C bond. The pi bonds in N≡N are formed from the p orbitals of nitrogen, which are more effective at overlapping due to the smaller size of nitrogen compared to carbon. This results in a stronger π-bond between nitrogen atoms.

Electronegativity and Electron Density

Nitrogen is more electronegative than carbon. This higher electronegativity results in a greater attraction between the bonded electrons and the nuclei of the nitrogen atoms. This increased electron density between the nitrogen nuclei strengthens the bond. The higher electronegativity of nitrogen leads to more compact and stable bonding, which further contributes to the higher bond energy of N≡N.

Lone Pair Repulsion and Bond Strength

Each nitrogen atom has a lone pair of electrons. In the case of N≡N, the lone pairs can interact favorably with the bonding electrons, enhancing the overall stability of the bond. This interaction also contributes to the higher bond energy. The ability of nitrogen to form these favorable interactions is an additional factor contributing to the higher bond energy.

Thermodynamic Stability

The N≡N bond is found in diatomic nitrogen (N2), a molecule that is highly stable under standard conditions. This stability is reflected in the high bond energy, approximately 941 kJ/mol. In contrast, while the C≡C bond is also strong (about 839 kJ/mol), it does not exhibit the same level of stability as N2, contributing to the higher bond energy observed for N≡N.

In summary, the higher bond energy of the N≡N triple bond compared to the C≡C triple bond can be attributed to better atomic overlap, the effects of electronegativity, and the overall stability of the nitrogen molecule. These factors collectively explain the higher bond energy of N≡N over C≡C.