lewis dot for ethane - Parker Core Knowledge

Understanding the Context

What is a Lewis Dot Structure?

A Lewis Dot structure, named after chemist Gilbert N. Lewis, uses dots to represent valence electrons around atoms. These diagrams simplify molecular bonding by showing how electrons are shared or transferred to form covalent or ionic bonds. The goal is to satisfy the octet rule—where atoms strive to have eight electrons in their outer shell—though exceptions exist, especially with lighter elements like carbon.

Lewis Dot Structure for Ethane (C₂H₆)

Key Insights

Ethane is a simple hydrocarbon with the molecular formula C₂H₆, consisting of two carbon atoms and six hydrogen atoms arranged in a single bonded two-carbon chain. Drawing its Lewis structure involves analyzing each atom’s valence electrons and forming bonds accordingly.

Step-by-Step Guide to Drawing the Lewis Dot Structure for Ethane

1. Count Total Valence Electrons
   Carbon (C) has 4 valence electrons; hydrogen (H) has 1 each.
   Ethane: (2 × 4 valence C) + (6 × 1 valence H) = 8 + 6 = 14 total valence electrons

2. Position the Atoms
   Place the two carbon atoms in the center, bonded by a double covalent bond (since ethane forms a single bond between the carbons and three single C–H bonds). Hydrogen atoms are terminal.

Final Thoughts

3. Form Single Bonds Between Carbons and Hydrogens
   Carbon–carbon single bond: uses 2 electrons
   Each Carbon forms three single bonds with Hydrogen atoms (3 × 2 electrons = 6 electrons used).
   Total electrons used so far: 2 (C–C) + 6 (C–H) = 8 electrons.

4. Distribute Remaining Electrons to Fulfill Octet Rule
   Remaining electrons: 14 – 8 = 6 electrons, placed as lone pairs.
   Carbon’s octet is nearly complete (already bonded via 4 electrons), so each Carbon forms three single bonds with Hydrogen atoms.
   After bonding:
   

   • Each Hydrogen has 2 electrons (meeting hydrogen’s duet).
     
   • Each Carbon has four bonds: two single C–H bonds and one C–C bond → requires 4 electrons in bonds only, plus 4 lone electrons to complete octet. But wait — carbon only needs 8 total valence electrons, and after bonding with two H’s via single bonds (2 electrons each), carbon forms four bonds, satisfying the octet.

Wait — correction: each single C–H bond contributes one shared pair (2 electrons), so each C bonds to two H’s via single bonds → total of 4 bonding electrons around each C, plus 4 lone electrons (from unshared pairs), totaling 8 electrons (the octet). Each H has 2 electrons, satisfying its duet.

5. Final Structure

H H | | C — H C — H

Both Carbon atoms are connected by a single bond, each bonded to three Hydrogen atoms, forming C₂H₆ — ethane.