Q68E - Chemistry (OpenStax)

Question

Describe the molecular structure of each of the following molecules or ions listed. You may wish to review the chapter on chemical bonding and molecular geometry.

(a) \({\rm{P}}{{\rm{H}}_3}\) 

(b) \({\rm{P}}{{\rm{H}}_4} + \)

(c) \({{\rm{P}}_2}{{\rm{H}}_4}\) 

(d) \({\rm{P}}{{\rm{O}}_4}^{3 - }\)

Step-by-Step Solution

Answer

a) \({\rm{P}}{{\rm{H}}_3}\):

b) \({\rm{P}}{{\rm{H}}_4} + \):

c) \({{\rm{P}}_2}{{\rm{H}}_4}\):

d) \({\rm{P}}{{\rm{O}}_4}^{3 - }\):

Step 1: Definition of molecular structure.

The placement of the atoms is described by molecular structure. We call the geometry that contains all electron pairs the electron-pair geometry to distinguish between these two circumstances. The molecular structure is the structure that solely comprises the location of the atoms in the molecule.

Step 2: Write the molecular structure of \({\rm{P}}{{\rm{H}}_3}\) .

a)

The structure of \({\rm{P}}{{\rm{H}}_3}\) is a trigonal pyramid, with three hydrogens in equal distance on one side of the phosphorus and a lone electron pair on the other. (See the illustration to the right.)

Step 3: Write the molecular structure of \({\rm{P}}{{\rm{H}}_4} + \) .

b)

The structure of \({\rm{P}}{{\rm{H}}_4} + \) is tetrahedral.

Step 4: Write the molecular structure of \({{\rm{P}}_2}{{\rm{H}}_4}\) .

c)

The \({{\rm{P}}_2}{{\rm{H}}_4}\)contains two phosphorus atoms with single bonds and two hydrogen atoms bound to each of them. It has a structure identical to ethane, but in gauche conformation (\({{\rm{P}}_2}{{\rm{H}}_4}\)).

Step 5: Write the molecular structure of \({\rm{P}}{{\rm{O}}_4}^{3 - }\) .

d)

The ion \({\rm{P}}{{\rm{O}}_4}^{3 - }\) has a tetrahedral structure. Although one double-bonded oxygen and one single-bonded oxygen are shown here, the electron that forms the double bond is displaced and continually moves from one P-O bond to the next.