Numford
Hybridisation

Hybridisation of PH₃

P is sp³ hybridised (hybridization by the VSEPR count): 3 sigma bonds and 1 lone pair give a trigonal pyramidal shape, bond angle about 93.5°.

HHPH
  • P
  • H
  • lone pair

PH₃Phosphine

Trigonal pyramidal

AB₃E: 3 bond pairs, 1 lone pair

  • Hybridisationsp³
  • Bond angleabout 93.5°
  • Polaritypolar

Why this shape

  1. P 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 P 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. P is larger and less electronegative than N, so the bond pairs sit farther from P and repel less. The angle closes to about 93.5 degrees, much less than 107 in NH3.
  5. The bond dipoles do not cancel in the trigonal pyramidal shape, so PH₃ is polar.

Lewis structure

8 valence electrons
PHHH

Formal charges: none

Working

Why this hybridisation and shape

  1. P 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 P 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. P is larger and less electronegative than N, so the bond pairs sit farther from P and repel less. The angle closes to about 93.5 degrees, much less than 107 in NH3.
  5. The bond dipoles do not cancel in the trigonal pyramidal shape, so PH₃ is polar.

Class 11, Chapter 4 Chemical Bonding and Molecular Structure.

Questions

Hybridisation of PH3: quick answers

What is the hybridisation of PH3?

P 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 P is sp³ hybridised.

What is the shape of PH3 and its bond angle?

Trigonal pyramidal, with a bond angle of about 93.5 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. P is larger and less electronegative than N, so the bond pairs sit farther from P and repel less. The angle closes to about 93.5 degrees, much less than 107 in NH3.

Is PH3 polar or non-polar?

Polar. The bond dipoles do not cancel in the trigonal pyramidal shape, so PH₃ is polar.

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