Lewis structure of C₂H₂
10 valence electrons. One C≡C triple bond and one C-H single bond, with no lone pair on C.
Lewis structure
10 valence electronsFormal charges: none
Why this shape
- Each C has 4 valence electrons. It uses four in one triple bond to C and one single bond to H, so none are left over.
- Steric number = two sigma bonds + no lone pairs = 2, so each C is sp hybridised. A double or triple bond counts once: only its sigma bond uses a hybrid orbital.
- Two electron pairs point in opposite directions, along a line (linear electron geometry). With no lone pairs the atoms take the same shape: linear.
- All the bond pairs repel each other equally, so the angle is the ideal 180°.
- The molecule is a straight line, so the two C-H bond dipoles cancel.
How to draw it
- Count the valence electrons: 2 × C 4 + 2 × H 1 = 10 valence electrons, 5 pairs.
- Join the atoms with single bonds: the C atoms to each other and the H atoms around them.
- Give each outer atom lone pairs until it has an octet (H needs only two electrons), then put any electrons left over on the central atom.
- Where an atom is still short of an octet, turn a lone pair of its neighbour into a shared pair: that makes a double or triple bond.
- Result: one C≡C triple bond and one C-H single bond, with no lone pair on C.
- Formal charge = valence electrons − lone pair electrons − number of bonds. Here: none.
Class 11, Chapter 4 Chemical Bonding and Molecular Structure.
Lewis structure of C2H2: quick answers
How many valence electrons are in C2H2?
2 × C 4 + 2 × H 1 = 10 valence electrons, 5 pairs.
What are the formal charges in the Lewis structure of C2H2?
Every atom has a formal charge of zero.
How many lone pairs are in the Lewis structure of C2H2?
0 in all, none on the central C.