Understanding the Context

What is H₂C₂?

H₂C₂ is a molecular formula representing a daimon in organic chemistry, most commonly referring to acetylene (C₂H₂)—a fundamental hydrocarbon consisting of two carbon atoms sharing a triple bond, each bonded to one hydrogen atom. While the formula appears simple, the Lewis structure reveals deep insights into electron sharing, molecular stability, and reactivity.

Step-by-Step Guide to Drawing the H₂C₂ Lewis Structure

Key Insights

Step 1: Count Valence Electrons

To build a correct Lewis structure, start by tallying total valence electrons from all atoms:

• Carbon (C) has 4 valence electrons; two carbons → 4 × 2 = 8 e⁻
  
• Hydrogen (H) has 1 electron each; two hydrogens → 1 × 2 = 2 e⁻
  
• Total valence electrons = 8 + 2 = 10 e⁻

Step 2: Identify the Central Atom

Carbon is more electronegative (3.5) than hydrogen (2.1), so it becomes the central atom, bonded to both H atoms.

Step 3: Form Single Bonds

Place two single bonds (C–H) using 4 electrons (2 bonds × 2 electrons):

H — C ≡ C — H

Final Thoughts

Now, subtract 4 e⁻ from the total → 6 e⁻ remain.

Step 4: Distribute Remaining Electrons

We’ve used 4 out of 10 → 6 electrons left, used in bonding. So 6 electrons remain as lone pairs.

Carbon typically forms a triple bond to satisfy its octet, so convert two C–H bonds into a C≡C triple bond using 8 electrons (4 pairs). That leaves 2 lone electrons on each carbon.

Remaining electrons: 10 – 8 = 2 e⁻ → assign 1 lone pair (2 e⁻) on each carbon.

Final arrangement:

• Central C–C bond: ≡ (triple bond)
  
• Each C holds one lone pair (🧥)
  
• Terminal H atoms: single-bonded as H–C

H — C ≡ C — H
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lone pair lone pair