# HCP Lewis structure

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HCP (methylidynephosphane) has one hydrogen atom, one carbon atom, and one phosphorus atom.

In HCP Lewis structure, there is a single bond between carbon and hydrogen atom, and a triple bond between carbon and phosphorus atom, and on the phosphorus atom, there is one lone pair.

Contents

## Steps

To properly draw the HCP Lewis structure, follow these steps:

#1 Draw a rough sketch of the structure
#2 Next, indicate lone pairs on the atoms
#3 Indicate formal charges on the atoms, if necessary
#4 Minimize formal charges by converting lone pairs of the atoms
#5 Repeat step 4 if necessary, until all charges are minimized

Let’s break down each step in more detail.

### #1 Draw a rough sketch of the structure

• First, determine the total number of valence electrons

In the periodic table, hydrogen lies in group 1, carbon lies in group 14, and phosphorus lies in group 15.

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

Since HCP has one hydrogen atom, one carbon atom, and one phosphorus atom, so…

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

And the total valence electrons = 1 + 4 + 5 = 10

• Second, find the total electron pairs

We have a total of 10 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 = 10 ÷ 2 = 5

• 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.

Now we have to choose the central atom from carbon and phosphorus. Place the least electronegative atom at the center.

Since phosphorus is less electronegative than carbon, the central atom should be phosphorus, right?

But if we place phosphorus in the center and carbon outside, and calculate the formal charge, then we do not get the formal charges on atoms closer to zero.

And the structure with the formal charges on atoms closer to zero is the best Lewis structure.

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

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

• And finally, draw the rough sketch

### #2 Next, indicate lone pairs on the atoms

Here, we have a total of 5 electron pairs. And two bonds are already marked. So we have to only mark the remaining three electron pairs as lone pairs on the sketch.

Also remember that hydrogen is a period 1 element, so it can not keep more than 2 electrons in its last shell. Carbon is a period 2 element, so it can not keep more than 8 electrons in its last shell. And phosphorus is a period 3 element, so it can keep more than 8 electrons in its last shell.

Always start to mark the lone pairs from outside atoms. Here, the outside atoms are hydrogen and phosphorus. But no need to mark on hydrogen, because hydrogen already has two electrons.

So for phosphorus, there are three lone pairs, and for carbon, there is zero lone pair because all three electron pairs are over.

Mark the lone pairs on the sketch as follows:

### #3 Indicate formal charges on the atoms, if necessary

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

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

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

For carbon atom, formal charge = 4 – 0 – ½ (4) = +2

For phosphorus atom, formal charge = 5 – 6 – ½ (2) = -2

Here, both carbon and phosphorus atoms have charges, so mark them on the sketch as follows:

The above structure is not a stable Lewis structure because both carbon and phosphorus atoms have charges. Therefore, reduce the charges (as below) by converting lone pairs to bonds.

### #4 Minimize formal charges by converting lone pairs of the atoms

Convert a lone pair of the phosphorus atom to make a new C — P bond with the carbon atom as follows:

### #5 Repeat step 4 (minimize charges again)

Since there are charges on carbon and phosphorus atoms, again convert a lone pair of the phosphorus atom to make a new C — P bond with the carbon atom as follows:

In the above structure, you can see that the central atom (carbon) forms an octet. The outside atom (phosphorus) also forms an octet, and hydrogen forms a duet. Hence, the octet rule and duet rule are satisfied.

Also, the above structure is more stable than the previous structures. Therefore, this structure is the stable Lewis structure of HCP.

Next: C2N2 Lewis structure