What is the Lewis structure for PBr3?

The Lewis structure for PBr₃ (phosphorus tribromide) can be drawn by following these straightforward steps:

1. Count the total number of valence electrons: Phosphorus (P) is in group 15 and thus has 5 valence electrons. Each bromine (Br) atom, being in group 17, has 7 valence electrons. Since there are three bromine atoms, the total for bromine is 3 x 7 = 21. So, the total number of valence electrons in PBr₃ is 5 + 21 = 26.
2. Identify the central atom: In PBr₃, phosphorus (P) acts as the central atom because it is less electronegative than bromine.
3. Place the central atom and bond the outer atoms: Place the phosphorus atom at the center and bond the three bromine atoms around it. Each P-Br bond uses 2 electrons. Since there are three bonds, that uses up 6 electrons (3 x 2 = 6).
4. Distribute the remaining electrons: After forming the bonds, we have 26 – 6 = 20 electrons left. These remaining electrons will be placed around the bromine atoms. Each bromine needs 6 more electrons to complete its octet. This accounts for 18 of the remaining electrons, placing 6 around each br atom (3 x 6 = 18). The last 2 electrons will be a lone pair on phosphorus.

Thus, the Lewis structure of PBr₃ shows phosphorus as the central atom with three single bonds to each bromine atom and one lone pair of electrons on the phosphorus. This arrangement helps illustrate the bonding and lone pairs in this molecule.

In summary, the final Lewis structure highlights the stable octets around the three bromines and captures the overall valence electron distribution in phosphorus tribromide.