MOLECULAR POLARITY FIELD NOTE 01 / 175
Is AlCl3 polar or nonpolar?
Three polar bonds. One symmetric arrangement. A zero net dipole.
An isolated AlCl₃ monomer has no permanent net dipole.
The molecule in space
Drag to turn the molecule. Plan view makes its three 120° angles easier to inspect.
01 / EXPERIMENTAL GEOMETRY The display uses NIST atom coordinates. Ball sizes and bond thickness are illustrative.
Why the dipoles cancel
Bond polarity and molecular polarity answer different questions. Follow the three observations below.
- 01
Each Al–Cl bond is polar.
Chlorine draws shared electron density toward itself. Each of the three bonds therefore has a dipole pointing from aluminum toward chlorine.
- 02
The bonds are evenly spaced.
Aluminum is at the center of a flat, trigonal arrangement. The three Cl–Al–Cl angles are 120°.
- 03
The vectors sum to zero.
The equal bond dipoles point in three directions separated by 120°. Their effects cancel, leaving the isolated monomer nonpolar.
This answer describes the monomer.
The four-atom model above is an isolated AlCl₃ unit. Aluminum chloride can also form Al₂Cl₆ dimers, including in vapor. The 120° drawing should not be used as the structure of every aluminum chloride sample.
Gas-phase structure study ↗Common questions about AlCl3
- 01
What does the Lewis structure of AlCl3 show?
In the isolated monomer, Al forms three single Al–Cl bonds. Each Cl has three lone pairs; Al has only six electrons around it. The condensed phase can contain Al2Cl6 dimers.
- 02
What is the molecular geometry of AlCl3?
The isolated AlCl3 monomer is trigonal planar. Al2Cl6 dimers have a different structure. The 3D model shows representative bond angles of 120°. These angles come from the displayed model coordinates.
- 03
What is the molar mass of AlCl3?
AlCl3 has an approximate molar mass of 133.33 g/mol, calculated from its formula using abridged standard atomic weights. Natural isotope variation can change the last digits.