Numford
Hybridisation

Hybridisation of AlCl₃

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

ClAlClCl
  • Al
  • Cl

AlCl₃Aluminium chloride

Trigonal planar

AB₃: 3 bond pairs, no lone pairs

i

This is the single AlCl3 molecule. In the vapour at lower temperature it pairs up as Al2Cl6, where each Al is sp3.

  • Hybridisationsp²
  • Bond angle120°
  • Polaritynon-polar

Why this shape

  1. Al has 3 valence electrons. It uses three in three single bonds to Cl, so none are left over.
  2. Steric number = three sigma bonds + no lone pairs = 3, so Al is sp² hybridised.
  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. All the bond pairs repel each other equally, so the angle is the ideal 120°.
  5. The bond dipoles cancel in the symmetric trigonal planar shape, so AlCl₃ is non-polar.

Lewis structure

24 valence electrons
i

Al has only six electrons around it, an incomplete octet.

AlClClCl

Formal charges: none

Working

Why this hybridisation and shape

  1. Al has 3 valence electrons. It uses three in three single bonds to Cl, so none are left over.
  2. Steric number = three sigma bonds + no lone pairs = 3, so Al is sp² hybridised.
  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. All the bond pairs repel each other equally, so the angle is the ideal 120°.
  5. The bond dipoles cancel in the symmetric trigonal planar shape, so AlCl₃ is non-polar.

Class 11, Chapter 4 Chemical Bonding and Molecular Structure.

Questions

Hybridisation of AlCl3: quick answers

What is the hybridisation of AlCl3?

Al has 3 valence electrons. It uses three in three single bonds to Cl, so none are left over. Steric number = three sigma bonds + no lone pairs = 3, so Al is sp² hybridised.

What is the shape of AlCl3 and its bond angle?

Trigonal planar, with a bond angle of 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. All the bond pairs repel each other equally, so the angle is the ideal 120°.

Is AlCl3 polar or non-polar?

Non-polar. The bond dipoles cancel in the symmetric trigonal planar shape, so AlCl₃ is non-polar.

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