Drawing the Lewis Structure for Ethane

Ethane is C2H6. Two carbons, six hydrogens, single bonds everywhere. It is one of the first molecules you are shown when learning Lewis structures, and for good reason — it is simple enough to get right, which makes getting it wrong a clear signal that something in your process needs fixing.

How to Build the Lewis Dot For Ethane Structure

Start by counting valence electrons. Carbon is in group 14, so it contributes 4 each. Hydrogen is group 1, so it contributes 1 each. That gives you 2 times 4 plus 6 times 1, which is 14 total valence electrons. Draw the carbon-carbon single bond first. That uses 2 electrons. Now attach three hydrogens to each carbon with single bonds. That is 6 more bonds per carbon side, so 12 more electrons used. Two plus twelve equals fourteen. All electrons accounted for. No lone pairs on either carbon. Each hydrogen has a full duet. Each carbon has a full octet. The structure looks like this in text form: H3C—CH3, with every bond represented as a pair of shared dots or a line. In actual dot notation, each bond is two dots between the atoms.

Common mistake: People sometimes draw a double bond between the carbons because they forget ethane is an alkane, not an alkene. If you do that, you run out of hydrogens or you exceed the electron count. Both are easy to catch if you verify after drawing.

A Real Problem I Ran Into

I was grading undergrad lab reports last semester and saw someone draw ethane with the two carbons sharing four electrons and only five hydrogens total. When I asked them how they got there, they said they "just combined the atoms" without doing the electron count first. The fix is straightforward: always do the valence count before drawing a single bond. It takes about ten seconds and catches 90 percent of structural errors students make on their first attempt.

Counter-Intuitive Things Beginners Miss

One thing that trips people up is that Lewis structures for ethane look almost identical whether you draw them with dots or lines. A line represents two electrons just as much as a pair of dots does. The dot format is technically more "accurate" to the original Lewis concept, but chemists overwhelmingly use lines for anything beyond the simplest molecules. Knowing when to switch matters. If you are in an intro class, draw the dots. If you are writing for a lab notebook or a paper, use lines and note that each line equals a bonding pair. Another thing: formal charge. For ethane, every atom has a formal charge of zero. Carbon has four bonds and zero lone pairs, so 4 minus 4 minus 0 equals zero. Hydrogen has one bond, so 1 minus 1 minus 0 equals zero. This might seem obvious, but checking formal charges is the fastest way to spot an incorrect structure on more complex molecules.

Limitations of the Lewis Model Here

Lewis structures for ethane tell you nothing about bond angles, molecular geometry, or the actual 3D shape. The carbons are sp3 hybridized and the H-C-H bond angles are approximately 109.5 degrees, but a Lewis diagram is flat and doesn't convey that. It also doesn't show anything about rotation around the C-C bond or the staggered versus eclipsed conformations. If you need any of that information, the Lewis structure is the wrong tool. Use a ball-and-stick model or a computational output instead.

Quick Reference Summary

- Molecular formula: C2H6 - Total valence electrons: 14 - Bonding pairs: 7 - Lone pairs: 0 - Carbon hybridization: sp3 - Geometry around each carbon: tetrahedral - All formal charges: zero