AlCl3 Lewis Structure
Aluminium chloride (aluminum chloride) · A Lewis acid catalyst for Friedel-Crafts reactions in organic chemistry.
The AlCl3 Lewis structure has 24 valence electrons, drawn as three Al–Cl bonds, with nine lone pairs in total. The central Al is sp2 hybridized, which makes it a trigonal planar molecule with a bond angle of 120 degrees. AlCl3 is nonpolar: the bond dipoles are all the same size and the shape places them symmetrically around the central Al, so they cancel exactly.
- 24 valence e−
- trigonal planar
- 120° bond angle
- sp2
- nonpolar
At least one atom does not reach a full octet in this structure.
AlCl3 molecular geometry
Trigonal planar, from 3 electron domains on the central Al: 3 bonded atoms (AX3). The electron geometry is trigonal planar. Wedges point toward you, hashed wedges away. Every shape in the VSEPR chart →
Calculated properties
| Total valence electrons | 24 |
|---|---|
| Bonding electrons | 6 (3 shared pairs) |
| Nonbonding electrons | 18 (9 lone pairs) |
| Lone pairs on Al | 0 |
| Electron domains (steric number) | 3 |
| VSEPR notation | AX3 |
| Electron geometry | trigonal planar |
| Molecular geometry | trigonal planar |
| Bond angle | 120° |
| Hybridization | sp2 |
| Polarity | nonpolar |
| Formal charges | all zero |
| Resonance structures | none |
| Molar mass | 133.332 g/mol |
Al Aluminium 3 valence e− Cl Chlorine 3 atoms, 7 valence e− each
How to draw the AlCl3 Lewis structure
Step through it. The bar shows how much of the 24-electron budget is spent at each stage - it never grows, which is the whole constraint.
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Skeleton. Join every connected pair with one bond. 3 bonds spends 6 electrons.
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Outer octets. Spend electrons as lone pairs on the outer atoms. That uses the entire budget, and the central atom has nothing left over.
The reasoning at each step
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Count the valence electrons
Add up the outer-shell electrons every atom brings. That total is the budget for the whole structure - every line and every dot has to come out of it, and nothing may be added.
3 (Al) + 3 x 7 (Cl) = 24 valence electrons -
Choose the central atom
Al is the least electronegative atom here, so it takes the centre. Hydrogen is never central: it can only form one bond.
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Join everything with single bonds first
Every connection starts as one shared pair. Draw them all before worrying about double bonds - the arithmetic in the next step is what tells you where the double bonds have to go.
3 bonds x 2 = 6 electrons used, 18 left -
Work out how far short you are
Add up what every atom still needs to fill its shell - eight electrons for most atoms, two for hydrogen - minus what its single bonds already give it. Compare that with the electrons you have left. The difference decides everything that follows.
needs 20, has 18, short by 2 -
Accept an incomplete octet
You are 2 electrons short, and the only way to close the gap would be a double bond to a halogen - which is not something these atoms do. Al stays below eight electrons instead. That is real chemistry, not a mistake.
Al: 6 electrons -
Fill in the lone pairs
Every electron not in a bond sits as a lone pair on an atom. Each atom takes exactly what it needs to finish its shell - there is no choice left at this point.
Cl1: 3, Cl2: 3, Cl3: 3 (18 electrons) -
Check the central atom
Al ends up with 6 electrons, short of an octet, which is correct for this molecule.
Al: 6 bonding + 0 nonbonding = 6 -
Check the formal charges
Formal charge is valence electrons, minus lone-pair electrons, minus the number of bonds. Every atom here comes out at zero, which is the sign of a good structure.
all formal charges = 0 -
Work out the shape
Count the electron domains on Al: 3 bonded groups. A double or triple bond still counts as one domain, because it points in one direction. That gives trigonal planar electron geometry; ignore the lone pairs and the atoms themselves sit in a trigonal planar arrangement.
steric number 3 -> sp2 -> trigonal planar, bond angle 120 -
Decide whether it is polar
The bond dipoles are all the same size and the shape places them symmetrically around the central Al, so they cancel exactly.
dipoles cancel -> nonpolar
Is AlCl3 polar or nonpolar?
AlCl3 is nonpolar. The bond dipoles are all the same size and the shape places them symmetrically around the central Al, so they cancel exactly.
| Bond | Electronegativity difference | Character |
|---|---|---|
| Al–Cl | 1.55 | polar covalent |
Common questions
How many valence electrons does AlCl3 have?
AlCl3 has 24 valence electrons. 6 of them are in bonds and 18 sit in lone pairs.
What is the molecular geometry of AlCl3?
AlCl3 is a trigonal planar molecule. The central Al has 3 bonded groups, a steric number of 3, which gives trigonal planar electron geometry and a trigonal planar molecule.
What is the bond angle in AlCl3?
The bond angle in AlCl3 is 120 degrees. That is the ideal trigonal planar angle, and nothing distorts it here.
What is the hybridization of AlCl3?
The central Al in AlCl3 is sp2 hybridized. Steric number 3 means 3 orbitals have to be mixed, which is exactly what sp2 gives you.
Is AlCl3 polar or nonpolar?
AlCl3 is nonpolar. The bond dipoles are all the same size and the shape places them symmetrically around the central Al, so they cancel exactly.