Ethylene contains a C=C double bond. Each carbon also forms two C–H single bonds, giving both carbon atoms complete octets and trigonal planar local geometry.
Two carbon atoms contribute eight valence electrons and four hydrogens contribute four, giving twelve total. A skeleton with a single C–C bond and four C–H bonds uses ten electrons but leaves each carbon with only six electrons. Converting the remaining pair into a second C–C bonding pair completes both octets.
How to draw the C2H4 Lewis structure
Count 12 valence electrons.
Use 4 from each carbon and 1 from each hydrogen.
Connect the two carbon atoms.
Attach two hydrogens to each carbon.
Draw the initial single bonds.
One C–C and four C–H bonds use 10 electrons.
Form a C=C double bond.
Use the remaining pair between the carbon atoms so both reach octets.
Check formal charges.
Every atom has formal charge zero.
Bonding and formal charges
The double bond contains one sigma bond and one pi bond. Each carbon participates in three sigma bonds and the shared pi bond. No lone pairs or formal charges occur on carbon in the standard structure.
Geometry and rotation
Each carbon has three electron domains and is trigonal planar. The p orbitals that form the pi bond must remain parallel, so free rotation around the C=C bond is restricted and the molecule is planar.
Common mistakes
Leaving a C–C single bond, which gives each carbon an incomplete octet.
Attaching three hydrogens to one carbon and one to the other.
Adding lone pairs to carbon instead of forming the double bond.
Calling each carbon tetrahedral; double-bonded carbons are trigonal planar.
Frequently asked questions
How many sigma and pi bonds are in C2H4?
Ethylene has five sigma bonds—four C–H and one C–C—and one pi bond.
What hybridization is assigned to each carbon?
Each carbon is commonly described as sp² hybridized.
Is C2H4 planar?
Yes. Both carbon centers and all four hydrogens lie approximately in one plane.