PH4+ Lewis structure

PH4+ (phosphonium) has one phosphorus atom and four hydrogen atoms.

In PH4+ Lewis structure, there are four single bonds around the phosphorus atom, with four hydrogen atoms attached to it, and none of the atoms has a lone pair.

Also, there is a positive (+1) charge on the phosphorus atom.

Contents

Steps

Use these steps to correctly draw the PH4+ Lewis structure:

#1 First draw a rough sketch
#2 Mark lone pairs on the atoms
#3 Calculate and mark formal charges on the atoms, if required

Let’s discuss each step in more detail.

#1 First draw a rough sketch

• First, determine the total number of valence electrons

In the periodic table, phosphorus lies in group 15, and hydrogen lies in group 1.

Hence, phosphorus has five valence electrons and hydrogen has one valence electron.

Since PH4+ has one phosphorus atom and four hydrogen atoms, so…

Valence electrons of one phosphorus atom = 5 × 1 = 5
Valence electrons of four hydrogen atoms = 1 × 4 = 4

Now the PH4+ has a positive (+1) charge, so we have to subtract one electron.

So the total valence electrons = 5 + 4 – 1 = 8

• Second, find the total electron pairs

We have a total of 8 valence electrons. And when we divide this value by two, we get the value of total electron pairs.

Total electron pairs = total valence electrons ÷ 2

So the total electron pairs = 8 ÷ 2 = 4

• Third, determine the central atom

Here hydrogen can not be the central atom. Because the central atom is bonded with at least two other atoms, and hydrogen has only one electron in its last shell, so it can not make more than one bond.

Hence, here we have to assume that the central atom is phosphorus.

Therefore, place phosphorus in the center and hydrogens on either side.

• And finally, draw the rough sketch

#2 Mark lone pairs on the atoms

Here, we have a total of 4 electron pairs. And four P — H bonds are already marked. So we do not have to mark any electron pair as a lone pair on the sketch.

#3 Calculate and mark formal charges on the atoms, if required

Use the following formula to calculate the formal charges on atoms:

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

For phosphorus atom, formal charge = 5 – 0 – ½ (8) = +1

For each hydrogen atom, formal charge = 1 – 0 – ½ (2) = 0

Here, the phosphorus atom has a charge, so mark it on the sketch as follows:

In the above structure, you can see that the central atom (phosphorus) forms an octet. And the outside atoms (hydrogens) also form a duet. Hence, the octet rule and duet rule are satisfied.

Therefore, this structure is the most stable Lewis structure of PH4+.

And since the PH4+ has a positive (+1) charge, mention that charge on the Lewis structure by drawing brackets as follows:

Next: SHF Lewis structure