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1800-102-2727Ethyne (C₂H₂) is also known as acetylene. It is a hydrocarbon with a linear structure and a triple bond between its two carbon atoms. It’s an excellent example of sp hybridisation in organic chemistry.
Let us understand how hybridisation happens in C₂H₂. Read on to learn how it leads to its bonding and molecular shape.
Ethyne consists of two carbon atoms and two hydrogen atoms. Each carbon atom is bonded to one hydrogen and the other carbon. In order to form these bonds and satisfy the octet rule, carbon undergoes sp hybridisation.
Ethyne/acetylene is renowned as the first and simplest form of Alkyne, possessing two carbon atoms linked with triple bonds. The triple bond is generally called an acetylenic bond.
Here is a complete understanding of its hybridisation.
The atomic number of carbon is 6.
The ground state of carbon :
1s² 2s² 2p²
Only two unpaired electrons → insufficient to form four bonds
Excited state configuration:

Four unpaired electrons → enough to form four bonds
Ground state vs excited state orbital diagram
sp hybridisation occurs when 1 s orbital and 1 p orbital mix.
The result:

Each carbon uses:
Result:
Geometry and bonding of ethyne
| Property | Details |
|---|---|
| Molecule | Ethyne (C₂H₂) |
| Hybridisation | sp |
| Geometry | Linear |
| Bond angle | 180° |
| Bonding | 3 σ bonds (2 C–H, 1 C–C), 2 π bonds (C≡C) |
| Unhybridised Orbitals | 2 (on each carbon for π bonding) |
| Carbon valency satisfied? | Yes, by forming 4 bonds |
To determine if the Lewis structure of C₂H₂ is stable, we calculate the formal charge on each atom using the formula:
Formal charge = Valence electrons – (Lone pair electrons + ½ × Bonding electrons)
Step-by-step for each atom:
Carbon (C) – each
Formal charge = 4 – (0 + ½ × 8) = 4 – 4 = 0
Hydrogen (H) – each
Formal charge = 1 – (0 + ½ × 2) = 1 – 1 = 0
Thus, all atoms in C₂H₂ carry zero formal charge, which confirms that the Lewis structure is stable and correct.
Each carbon in C₂H₂ forms 4 bonds: 1 with hydrogen and 3 with another carbon (1 σ and 2 π). sp hybridisation leads to a linear shape and 180° bond angles. The π bonds are responsible for the triple bond between the carbon atoms.
Q1. Why does carbon undergo hybridisation in C₂H₂?
To form 4 covalent bonds, carbon promotes an electron and mixes orbitals to form hybrid orbitals.
Q2. How many σ and π bonds are present in C₂H₂?
There are 3 σ bonds and 2 π bonds in total.
Q3. What is the shape of ethyne?
Linear, due to sp hybridisation.
Q4. Is C₂H₂ polar or non-polar?
Ethyne is non-polar, as the bond dipoles cancel due to the linear geometry.
Q5. What are some uses of alkyne in our lives?
Alkyne is commercially used in the ripening of fruits. It helps fuel in welding torches, and in many polymers. It can be used as fuel.