C3H4 Lewis structure

C₃H₄ (propyne) has three carbon atoms and four hydrogen atoms.

In C₃H₄ Lewis structure, there is one triple bond and one single bond between the three carbon atoms. The left carbon is attached with one hydrogen atom, and the right carbon is attached with three hydrogen atoms. And none of the atoms has a lone pair.

Alternative method: Lewis structure of C₃H₄

Rough sketch

• First, determine the total number of valence electrons

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

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

Since C₃H₄ has three carbon atoms and four hydrogen atoms, so…

Valence electrons of three carbon atoms = 4 × 3 = 12
Valence electrons of four hydrogen atoms = 1 × 4 = 4

And the total valence electrons = 12 + 4 = 16

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

• Second, find the total electron pairs

We have a total of 16 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 = 16 ÷ 2 = 8

• 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 there are three atoms remaining and all three atoms are carbon, so we can assume any one as the central atom.

Let’s assume that the central atom is center carbon.

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

• And finally, draw the rough sketch

Lone pair

Here, we have a total of 8 electron pairs. And six bonds are already marked. So we have to only mark the remaining two electron pairs as lone pairs on the sketch.

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

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

So for left carbon, there are two lone pairs, and for other two carbons, there is zero lone pair because all two 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 left carbon atom, formal charge = 4 – 4 – ½ (4) = -2

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

For right carbon atom, formal charge = 4 – 0 – ½ (8) = 0

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

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

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

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

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

Final structure

The final structure of C₃H₄ (specifically propyne, the most stable isomer) consists of three carbon atoms linked in a chain, where the first two carbons share a triple covalent bond and the second and third carbons share a single covalent bond. In this arrangement, all three carbon atoms satisfy the octet rule: the terminal alkyne carbon forms a triple bond to its neighbor and a single bond to one hydrogen, the central carbon forms a triple and a single bond to its carbon neighbors, and the third carbon forms a single bond to the central carbon and three single bonds to hydrogen atoms. Every hydrogen atom reaches its stable duet state through these single shared pairs. This configuration is the most stable because it results in formal charges of zero for all atoms, representing the most energetically favorable state for the molecule. Consequently, this specific electronic distribution serves as the definitive and most accurate Lewis representation for this hydrocarbon.

Next: PI₃ Lewis structure

External video

• C3H4 Lewis Structure: How to Draw the Lewis Structure for CH3CCH – YouTube • Wayne Breslyn

External links

• https://www.numerade.com/ask/question/what-is-c3h4-lewis-structure-electronic-geometry-of-each-carbon-and-molecular-geometry-of-each-carbon-what-would-a-sketch-look-like-would-they-all-be-tetrahedral-43372/
• https://homework.study.com/explanation/draw-the-lewis-structure-for-c3h4.html
• https://www.chegg.com/homework-help/questions-and-answers/lewis-structure-c3h4-contains-three-carbon-atoms-connected-successively-double-bonds-two-h-q24736772
• https://brainly.com/question/11730596