Drawing the Lewis Structure for PCl5

Viewing Notes:

  • PCl5 is similar to PBr5 and PF5. If you can do those Lewis structures PCl5 will be easy.
  • In the PCl5 Lewis structure Phosphorus (P) is the least electronegative so it goes in the center.
  • In the Lewis structure for PCl5 there are a total of 40 valence electrons. Five pairs will be used in the chemical bonds between the P and Cl.

Transcript: Hi, this is Dr. B. Let's do the PCl5 Lewis structure. Phosphorus, on the periodic table: group 5, 5 valence electrons. Chlorine, group 7; 7 valence electrons but we have 5 of those, so we need to multiply that times 5 for a total of (5 + 35) 40 valence electrons. We'll put the Phosphorus in the center and then along the outside, we'll put the Chlorines. So we have 5, and there they are. We'll draw a line between each Phosphorus and Chlorine which will represent a chemical bond. That's a pair of valence electrons there. So we have 1, 2, 3, 4, 5; we've used 10 valence electrons. Now we'll go around the outer atoms and put valence electrons on those until we use the rest up. So we have 10, 12, 14, and 40.

At this point, we've used all the valence electrons. All of the Chlorines, they're symmetrical, and they have 2, 4, 6, plus this line right here, 8 valence electrons; so all the Chlorines have octets. The Phosphorus in the center actually has 10 valence electrons, but that's OK. Phosphorus is in period 3 or row 3 of the periodic table, and those elements and the ones below them can have more than 8 valence electrons. So we've used all of our valence electrons, all 40. We've got the structure here. We could check our formal charges if we wanted to make sure. If we did, we'd find they were all zero.

So this is the Lewis structure for PCl5. This is Dr. B.; thanks for watching.