HCP Lewis structure

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.

Alternative method: Lewis structure of HCP

Rough sketch

• 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

Learn how to find: Hydrogen valence electrons, Carbon valence electrons, and Phosphorus valence electrons

• 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

Lone pair

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:

Formal charge

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.

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

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:

Final structure

The final structure of HCP consists of a central carbon atom linked to a hydrogen atom and a phosphorus atom. In this configuration, the carbon atom satisfies the octet rule by forming a single covalent bond with the hydrogen and a triple covalent bond with the phosphorus. Within this layout, the phosphorus atom also fulfills the octet rule by maintaining one lone pair alongside its triple bond, while the hydrogen atom achieves a stable duet. This arrangement represents the most stable state for the molecule because it results in a formal charge of zero for every atom involved. Accordingly, this specific electronic distribution serves as the definitive and most accurate Lewis representation of phosphaethyne.

Next: C₂N₂ Lewis structure

External links

• https://www.answers.com/chemistry/What_is_the_Lewis_structure_for_HCP
• https://oneclass.com/homework-help/chemistry/6920028-hcp-lewis-structure.en.html
• https://www.numerade.com/questions/write-lewis-structures-for-mathrmhcp-and-leftmathrmiof_4right-use-vsepr-theory-to-predict-the-electr/
• https://www.chegg.com/homework-help/questions-and-answers/draw-correct-lewis-structure-hcp-molecule-correct-lewis-structure-shows-select-answer-subm-q85284611