How many sigma (?) bonds and pi (?) bonds are there in the best Lewis structure for HNNH (N?H?)? The atoms are connected in the order given. 3 sigma bond and no pi bonds 2 sigma bonds and 1 pi bond 2 sigma bonds and 2 pi bonds 3 sigma bonds and 1 pi bonds 3 sigma bonds and 2 pi bonds
The Correct Answer and Explanation is:
To determine the number of sigma and pi bonds in HNNH (diazene), we first need to construct its best Lewis structure. The atoms are arranged in the given order: hydrogen bonded to nitrogen, nitrogen bonded to nitrogen, and nitrogen bonded to hydrogen.
Step 1: Count Valence Electrons
- Hydrogen has 1 valence electron
- Nitrogen has 5 valence electrons
- Total valence electrons: (2 × 1) + (2 × 5) = 12
Step 2: Arrange Atoms
- Connect atoms with single bonds: H-N-N-H
- Each single bond is a sigma bond
Step 3: Distribute Remaining Electrons
- The two hydrogen atoms are already stable with two electrons each
- Each nitrogen needs an octet (8 electrons)
- Placing lone pairs on nitrogen fulfills the octet rule
Step 4: Consider Multiple Bonds
- If both nitrogen atoms had only single bonds, each would have only 6 electrons, violating the octet rule
- A second bond is required between the nitrogen atoms to complete their octets
- This additional bond is a pi bond
Step 5: Count Bonds
- Three sigma bonds: one in the N=N bond and two in N-H bonds
- One pi bond: part of the N=N double bond
Thus, the correct answer is three sigma bonds and one pi bond. The presence of the double bond ensures proper electron distribution for nitrogen atoms. This structure maintains stability while adhering to the octet rule.
