Draw the Lewis structure for the ethylene (C2H4) molecule. Be sure to include all resonance structures that satisfy the octet rule.
The correct answer and explanation is:
Lewis Structure for Ethylene (C₂H₄)
Correct Lewis Structure:
H H
\ /
C==C
/ \
H H
- Each carbon (C) atom forms three sigma bonds (two with hydrogen and one with another carbon) and one pi bond (in the carbon-carbon double bond).
- Each hydrogen (H) forms one single bond with a carbon atom.
Explanation (300 Words):
Ethylene, or C₂H₄, is the simplest alkene, featuring a double bond between two carbon atoms. The total number of valence electrons must be determined first to draw its Lewis structure correctly.
- Carbon (C) has 4 valence electrons, and there are 2 carbon atoms:
4 × 2 = 8 electrons - Hydrogen (H) has 1 valence electron, and there are 4 hydrogen atoms:
1 × 4 = 4 electrons - Total valence electrons = 8 + 4 = 12 electrons
We use these 12 electrons to form bonds and satisfy the octet rule for carbon and the duet rule for hydrogen.
Each carbon atom bonds with two hydrogen atoms and shares a double bond with the other carbon. This arrangement uses:
- 4 single bonds between carbon and hydrogen = 4 × 2 = 8 electrons
- 1 double bond between carbon atoms = 4 electrons
- Total used: 8 + 4 = 12 electrons — all valence electrons accounted for.
In this structure:
- Each hydrogen has 2 electrons (1 bond) — satisfying the duet rule.
- Each carbon has 4 bonds (8 electrons) — satisfying the octet rule.
Resonance Structures:
Ethylene does not have any valid resonance structures. The double bond is localized between the two carbon atoms. Unlike molecules like ozone (O₃) or benzene (C₆H₆), where electrons can be delocalized over multiple atoms, ethylene’s π electrons are fixed between the two carbon atoms, forming a localized double bond. Therefore, only one valid Lewis structure satisfies the octet rule.
Thus, the single Lewis structure above accurately represents ethylene.