The Lewis structure for boron trichloride (BCl3) can be illustrated as follows:
Cl
|
Cl-B-Cl
|
Cl
In this structure, boron (B) is the central atom bonded to three chlorine (Cl) atoms. To understand why BCl3 does not follow the octet rule, let’s take a closer look at its electronic configuration and bonding.
Boron has three valence electrons, while each chlorine atom has seven valence electrons. When forming BCl3, boron shares its three electrons with the three chlorines. Each chlorine atom receives one electron from boron to complete their octets, while boron ends up with only six electrons in its valence shell (three from the single covalent bonds with the three Cl atoms).
This is an example of a molecule that does not satisfy the octet rule, as boron is stable with fewer than eight electrons. This is a common characteristic for elements in group 13, where boron is located. Its ability to form stable compounds with an incomplete octet is due to its position in the periodic table and its tendency to engage in bonding frameworks where it can achieve stability through sharing and hybridization.