Numford
Hybridisation

Hybridisation of NH₃

N is sp³ hybridised (hybridization by the VSEPR count): 3 sigma bonds and 1 lone pair give a trigonal pyramidal shape, bond angle 107°.

HHNH
  • N
  • H
  • lone pair

NH₃Ammonia

Trigonal pyramidal

AB₃E: 3 bond pairs, 1 lone pair

  • Hybridisationsp³
  • Bond angle107°
  • Polaritypolar

Why this shape

  1. N has 5 valence electrons. It uses three in three single bonds to H, so two are left as one lone pair.
  2. Steric number = three sigma bonds + one lone pair = 4, so N is sp³ hybridised.
  3. Four electron pairs point to the corners of a tetrahedron (tetrahedral electron geometry). With one lone pair in place of atoms, the atoms make a trigonal pyramidal shape.
  4. Repulsion falls in the order lone pair to lone pair > lone pair to bond pair > bond pair to bond pair. The lone pair pushes the bond pairs closer, so the angle is 107°, less than the ideal 109.5°.
  5. The bond dipoles do not cancel in the trigonal pyramidal shape, so NH₃ is polar.

Lewis structure

8 valence electrons
NHHH

Formal charges: none

Working

Why this hybridisation and shape

  1. N has 5 valence electrons. It uses three in three single bonds to H, so two are left as one lone pair.
  2. Steric number = three sigma bonds + one lone pair = 4, so N is sp³ hybridised.
  3. Four electron pairs point to the corners of a tetrahedron (tetrahedral electron geometry). With one lone pair in place of atoms, the atoms make a trigonal pyramidal shape.
  4. Repulsion falls in the order lone pair to lone pair > lone pair to bond pair > bond pair to bond pair. The lone pair pushes the bond pairs closer, so the angle is 107°, less than the ideal 109.5°.
  5. The bond dipoles do not cancel in the trigonal pyramidal shape, so NH₃ is polar.

Class 11, Chapter 4 Chemical Bonding and Molecular Structure.

Questions

Hybridisation of NH3: quick answers

What is the hybridisation of NH3?

N has 5 valence electrons. It uses three in three single bonds to H, so two are left as one lone pair. Steric number = three sigma bonds + one lone pair = 4, so N is sp³ hybridised.

What is the shape of NH3 and its bond angle?

Trigonal pyramidal, with a bond angle of 107 degrees. Four electron pairs point to the corners of a tetrahedron (tetrahedral electron geometry). With one lone pair in place of atoms, the atoms make a trigonal pyramidal shape. Repulsion falls in the order lone pair to lone pair > lone pair to bond pair > bond pair to bond pair. The lone pair pushes the bond pairs closer, so the angle is 107°, less than the ideal 109.5°.

Is NH3 polar or non-polar?

Polar. The bond dipoles do not cancel in the trigonal pyramidal shape, so NH₃ is polar.

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