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.

Question

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

To determine how the covalent bonds form in phosphorus trichloride (PCl₃), we first need to analyze the electron configurations of phosphorus and chlorine and how they will share their electrons.

Phosphorus (P) has 5 valence electrons (2 in the inner shell and 5 in the third circle). Chlorine (Cl) has 7 valence electrons (2 in the inner shell, 8 in the middle, and 7 in the outer shell).

In phosphorus trichloride, phosphorus will form three covalent bonds with three chlorine atoms. Each chlorine atom will share one of its valence electrons with phosphorus to complete its octet, while phosphorus shares one of its five valence electrons to achieve a stable configuration.

Given the possible diagrams:

1. The first option indicates phosphorus sharing two pairs with one chlorine and a pair with each of the other two chlorines, which is incorrect as phosphorus only forms three bonds.
2. The second option suggests phosphorus has four shared pairs, which is also incorrect.
3. The third option shows phosphorus bonding with three chlorines and still having two unshared electrons (lone pairs) on phosphorus, which aligns with phosphorus's valency and its electron configuration.
4. The fourth option also indicates phosphorus sharing three pairs, but does not properly represent the lone pair on phosphorus.

The best representation for covalent bonding in phosphorus trichloride is the third option, as it accurately depicts phosphorus with three bonds to three chlorine atoms, while also retaining two unshared electrons (lone pairs) on phosphorus.

Therefore, the most appropriate diagram is the third option.