To draw the Lewis dot structure of aluminum chloride (AlCl3), we start by determining the total number of valence electrons available. Aluminum (Al) has 3 valence electrons, and each chlorine (Cl) has 7 valence electrons. Since there are three chlorine atoms, the total is:
- Valence electrons from Al: 3
- Valence electrons from 3 Cl: 3 × 7 = 21
This gives us a total of 3 + 21 = 24 valence electrons.
Next, we place the central atom (Al) and surround it with the three Cl atoms:
We then connect each chlorine atom to the aluminum atom with a single bond. Each bond consists of 2 electrons, so we consume 6 electrons (3 bonds × 2 electrons). This leaves us with:
- Remaining valence electrons: 24 – 6 = 18
Chlorine atoms need to complete their octet. Each Cl atom will receive 6 additional electrons (3 lone pairs) to achieve 8 electrons. Thus, we’ve used 18 electrons on the three Cl atoms, and each Cl has 8 electrons:
- Electrons used for Cl: 18 electrons (6 each for 3 Cl)
Now, the structure satisfies the octet rule for Cl but not for Al. Aluminum only has 6 electrons around it, showing an incomplete octet. Therefore, the formal charge on Al is:
Formal Charge on Al:
FC = Valence electrons - (Non-bonding electrons + 0.5 × Bonding electrons)
FC = 3 - (0 + 0.5 × 6) = 3 - 3 = 0
For chlorine atoms, each Cl has:
Formal Charge on Cl:
FC = 7 - (6 + 0.5 × 2) = 7 - (6 + 1) = 7 - 7 = 0
Thus, in the Lewis structure of AlCl3, all atoms have a formal charge of 0.
As for resonance structures, AlCl3 does not have resonance forms in the traditional sense, as there are no other electron arrangements that can redistribute the bonding without creating the same overall structure. The molecule primarily exists in the one structure shown above, handling the interactions as an ionic compound in several contexts.
In summary, aluminum chloride features a central aluminum atom bonded to three chlorine atoms, each with completed octets, and exhibits formal charges of zero for all atoms in the molecule.