Numford
Hybridisation

Hybridisation of HCN

C is sp hybridised (hybridization by the VSEPR count): 2 sigma bonds and no lone pairs give a linear shape, bond angle 180°.

NCH
  • C
  • H
  • N

HCNHydrogen cyanide

Linear

AB₂: 2 bond pairs, no lone pairs

  • Hybridisationsp
  • Bond angle180°
  • Polaritypolar

Why this shape

  1. C has 4 valence electrons. It uses four in one single bond to H and one triple bond to N, so none are left over.
  2. Steric number = two sigma bonds + no lone pairs = 2, so C is sp hybridised. A double or triple bond counts once: only its sigma bond uses a hybrid orbital.
  3. Two electron pairs point in opposite directions, along a line (linear electron geometry). With no lone pairs the atoms take the same shape: linear.
  4. All the bond pairs repel each other equally, so the angle is the ideal 180°.
  5. The bond dipoles do not cancel in the linear shape, so HCN is polar.

Lewis structure

10 valence electrons
CHN

Formal charges: none

Working

Why this hybridisation and shape

  1. C has 4 valence electrons. It uses four in one single bond to H and one triple bond to N, so none are left over.
  2. Steric number = two sigma bonds + no lone pairs = 2, so C is sp hybridised. A double or triple bond counts once: only its sigma bond uses a hybrid orbital.
  3. Two electron pairs point in opposite directions, along a line (linear electron geometry). With no lone pairs the atoms take the same shape: linear.
  4. All the bond pairs repel each other equally, so the angle is the ideal 180°.
  5. The bond dipoles do not cancel in the linear shape, so HCN is polar.

Class 11, Chapter 4 Chemical Bonding and Molecular Structure.

Questions

Hybridisation of HCN: quick answers

What is the hybridisation of HCN?

C has 4 valence electrons. It uses four in one single bond to H and one triple bond to N, so none are left over. Steric number = two sigma bonds + no lone pairs = 2, so C is sp hybridised. A double or triple bond counts once: only its sigma bond uses a hybrid orbital.

What is the shape of HCN and its bond angle?

Linear, with a bond angle of 180 degrees. Two electron pairs point in opposite directions, along a line (linear electron geometry). With no lone pairs the atoms take the same shape: linear. All the bond pairs repel each other equally, so the angle is the ideal 180°.

Is HCN polar or non-polar?

Polar. The bond dipoles do not cancel in the linear shape, so HCN is polar.

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