Numford
Hybridisation

Hybridisation of HNO₃

N is sp² hybridised (hybridization by the VSEPR count): 3 sigma bonds and no lone pairs give a trigonal planar shape, bond angle about 120°.

HONOO
  • N
  • O
  • H

HNO₃Nitric acid

Trigonal planar

AB₃: 3 bond pairs, no lone pairs

  • Hybridisationsp²
  • Bond angleabout 120°
  • Polaritypolar

Why this shape

  1. N has 5 valence electrons. In the Lewis structure it makes one double bond to O and two single bonds to O and keeps no lone pair, which leaves it a formal charge of +1.
  2. Steric number = three sigma bonds + no lone pairs = 3, so N is sp² hybridised. A double or triple bond counts once: only its sigma bond uses a hybrid orbital.
  3. Three electron pairs point to the corners of a flat triangle (trigonal planar electron geometry). With no lone pairs the atoms take the same shape: trigonal planar.
  4. There is no lone pair on N, but the three N-O bonds are not alike (a double bond, a single bond and N-OH), so the angles are near 120 degrees, not all equal.
  5. The bond dipoles do not cancel in the trigonal planar shape, so HNO₃ is polar.

Lewis structure

24 valence electrons
i

As in NCERT Table 4.1: N carries +1 and the single bonded O carries -1.

NOOOH+−

Formal charges: N +1, O −1

Working

Why this hybridisation and shape

  1. N has 5 valence electrons. In the Lewis structure it makes one double bond to O and two single bonds to O and keeps no lone pair, which leaves it a formal charge of +1.
  2. Steric number = three sigma bonds + no lone pairs = 3, so N is sp² hybridised. A double or triple bond counts once: only its sigma bond uses a hybrid orbital.
  3. Three electron pairs point to the corners of a flat triangle (trigonal planar electron geometry). With no lone pairs the atoms take the same shape: trigonal planar.
  4. There is no lone pair on N, but the three N-O bonds are not alike (a double bond, a single bond and N-OH), so the angles are near 120 degrees, not all equal.
  5. The bond dipoles do not cancel in the trigonal planar shape, so HNO₃ is polar.

Class 11, Chapter 4 Chemical Bonding and Molecular Structure.

Questions

Hybridisation of HNO3: quick answers

What is the hybridisation of HNO3?

N has 5 valence electrons. In the Lewis structure it makes one double bond to O and two single bonds to O and keeps no lone pair, which leaves it a formal charge of +1. Steric number = three sigma bonds + no lone pairs = 3, so N is sp² hybridised. A double or triple bond counts once: only its sigma bond uses a hybrid orbital.

What is the shape of HNO3 and its bond angle?

Trigonal planar, with a bond angle of about 120 degrees. Three electron pairs point to the corners of a flat triangle (trigonal planar electron geometry). With no lone pairs the atoms take the same shape: trigonal planar. There is no lone pair on N, but the three N-O bonds are not alike (a double bond, a single bond and N-OH), so the angles are near 120 degrees, not all equal.

Is HNO3 polar or non-polar?

Polar. The bond dipoles do not cancel in the trigonal planar shape, so HNO₃ is polar.

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