Chemical Bonding And Molecular Structure

Step 1: Recall bond length fundamentals
Bond length decreases with increasing bond order according to:
Step 2: Determine bond orders using MOT
Molecular orbital configuration for oxygen species: Bond order calculation:

• :
• : (removes antibonding electron)
• : (adds antibonding electron)
• : (adds 2 antibonding electrons)

Step 3: Establish bond length order
Since bond length :
Step 4: Experimental validation
Measured bond lengths:

• : 112 pm (shortest)
• : 121 pm
• : 133 pm
• : 149 pm (longest)

Step 1: Understand molecular polarity
A polar molecule must have:

• Polar bonds (electronegativity difference)
• Asymmetric geometry (net dipole moment)

Step 2: Analyze each option
\begin{tabular}{lll} Molecule & Geometry & Polarity
& Trigonal planar & Nonpolar (symmetrical)
& Square planar & Nonpolar (symmetrical)
& Tetrahedral & Nonpolar (symmetrical)
& Trigonal pyramidal & Polar (asymmetric)
\end{tabular}
Step 3: Verify polarity

• N-H bonds are polar (EN difference)
• Lone pair creates asymmetric charge distribution
• Net dipole moment exists

Step 4: Why others are nonpolar

• : Symmetric despite polar B-F bonds
• : Symmetric square planar cancels dipoles
• : Symmetric tetrahedral cancels dipoles