##PBr_5##’s is trigonal bipyramidal.
Let’s start with its . ##P## has 5 and ##Br## has 7 , which means that a total of ##5 + 5*7 = 40## electrons must be accounted for.
##P##’s bonds with the five ##Br## atoms account for ##5 * 2 = 10## electrons, while the three lone pairs on each ##Br## atom complete the rest of the electrons – ##5 * 6 =30## electrons.
SInce ##P## forms bonds with 5 other atoms and has no lone pairs, it has a steric number and a coordination number equal to 5 . According to , this corresponds to a trigonal bipyramidal molecular geometry.
