Draw and Explain the Lewis Structure for BCl3: Does This Molecule Have a Central Atom That Violates the Octet Rule? Explain.

The Lewis structure for boron trichloride (BCl₃) can be drawn by following these steps:

1. Count the total number of valence electrons: Boron (B) has 3 valence electrons, and each chlorine (Cl) has 7, giving:
• Total = 3 (B) + 3 x 7 (Cl) = 24 valence electrons
2. Determine the central atom: Boron is less electronegative than chlorine, so it will be the central atom.
3. Connect the central atom (B) to the three chlorine atoms (Cl) with single bonds. Each bond uses 2 electrons:
• 3 bonds x 2 electrons/bond = 6 electrons used
4. Place the remaining electrons around the chlorine atoms to satisfy their octets: Each chlorine will have 3 lone pairs (6 electrons) and one bond, reaching a total of 8 electrons.
5. At this point, boron has only 6 electrons around it (from the three single bonds with chlorine), which means it does not complete an octet.

The final Lewis structure of BCl₃ looks like this:

    Cl
     |  
  Cl-B-Cl

In this structure, the chlorine atoms each have a complete octet (8 electrons), while boron has only 6 electrons surrounding it. This leads to the conclusion that BCl₃ has a central atom (boron) that does indeed violate the octet rule.

Typically, the octet rule states that atoms should have 8 electrons in their valence shell to be stable. However, boron is an exception. It is capable of being stable with less than 8 electrons, as it can accommodate only 6. This characteristic is particularly common for elements in group 13 of the periodic table, where boron is found.