The Lewis structure for C2H2 contains: a) how many single bonds, b) how many double bonds, c) how many triple bonds and d) how many lone pairs?
The correct answer and explanation is:
Correct Answers:
a) 2 single bonds
b) 0 double bonds
c) 1 triple bond
d) 2 lone pairs
Explanation (Approx. 300 words):
C₂H₂ is the molecular formula for ethyne, also known as acetylene. To determine the bonding and lone pairs in its Lewis structure, we follow a systematic approach.
Step 1: Count the valence electrons.
- Carbon (C) has 4 valence electrons, and there are two carbon atoms: 4 × 2 = 8
- Hydrogen (H) has 1 valence electron, and there are two hydrogen atoms: 1 × 2 = 2
- Total = 8 + 2 = 10 valence electrons
Step 2: Determine the bonding arrangement.
Ethyne is a linear molecule. The skeletal structure places the carbon atoms bonded to each other, with each carbon also bonded to one hydrogen:
H–C≡C–H
Between the two carbon atoms, a triple bond forms, using 6 electrons (3 shared pairs). Each hydrogen is connected to a carbon by a single bond, using 2 more electrons (1 pair per H–C bond). So far, 8 electrons are used (6 in the triple bond and 1 each in the two C–H single bonds). That leaves 2 electrons, or 1 lone pair.
Each carbon atom follows the octet rule. In the structure:
- Carbon atoms share 6 electrons with each other and 2 electrons with hydrogen, totaling 8.
- Hydrogen atoms follow the duet rule (only need 2 electrons), satisfied by the single C–H bonds.
Step 3: Assign lone pairs.
Hydrogen never has lone pairs. The remaining 2 electrons are assigned as lone pairs. In the Lewis structure, each carbon atom has one lone pair, totaling 2 lone pairs.
Summary:
- Single bonds: 2 (each C–H)
- Double bonds: 0
- Triple bonds: 1 (between the carbon atoms)
- Lone pairs: 2 (1 on each carbon)
This structure satisfies the octet rule for carbon and duet rule for hydrogen.