Question

Phosphorous (P) and chlorine (Cl) bond covalently to form the important industrial compound phosphorous trichloride. The diagrams below show the electron structures of phosphorous and chlorine.

On left, a purple circle labeled P surrounded by 3 concentric circles. The inner circle has 2 small green spheres. The second circle has 8 small green spheres. The third circle has 5 small green spheres. On right, a purple circle labeled C l surrounded by 3 concentric circles. The inner circle has 2 small green spheres. The middle circle has 8 small green spheres. The outer circle has 7 small green spheres.
Which diagram shows how the covalent bonds most likely form in a phosphorous trichloride molecule?

At center, P connected above by 2 lines to C l with 2 dots each on right, left, top. Also connected by 1 line at left to C l with 2 dots each above, below, left. Also connected by 1 line at right to C l with 2 dots each above, below, right.

At center, P connected above by 2 lines to C l with 2 dots each on right, left, top. Also connected by 2 lines at left to C l with 2 dots each above, left. Also connected by 2 lines at right to C l with 2 dots each above, right.

At center, P connected above by 1 line to C l with 2 dots each on right, left, top. Also connected by 1 line at left to C l with 2 dots each above, below, left. Also connected by 1 line at right to C l with 2 dots each above, below, right. P also has 2 dots below.

At center, P connected above by 2 lines to C l with 2 dots each on right, left, top. Also connected by 1 line at left to C l with 2 dots each above, below. Also connected by 1 line at right to C l with 2 dots each above, below.

Answer 1

The third diagram — P with three single bonds to Cl and one lone pair (two dots) on P.

Reason: P has 5 valence electrons and forms three single covalent bonds to three Cl atoms (each Cl shares one electron), leaving P with one lone pair. Each Cl has three lone pairs plus the shared bonding pair to complete its octet.