To draw the Lewis structure for ethyne (C2H2), we start by determining the total number of valence electrons. Carbon has 4 valence electrons, and hydrogen has 1. Therefore, for C2H2:
Total valence electrons: (2 × 4) + (2 × 1) = 8 + 2 = 10 electrons
Next, we need to arrange the atoms. Ethyne is a linear molecule, with a triple bond between the two carbon atoms and a single bond between each carbon and hydrogen. The structure can be represented as:
C≡C
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H H
Here, the triple bond between the carbon atoms accounts for 6 electrons (3 bonds), and each carbon is bonded to one hydrogen (2 electrons total). This accounts for all 10 valence electrons.
Now, we need to calculate the formal charge on each carbon atom. The formula for formal charge is:
Formal Charge = Valence Electrons – (Non-bonding Electrons + 0.5 × Bonding Electrons)
Each carbon in the C2H2 molecule has:
- Valence electrons: 4
- Non-bonding electrons: 0
- Bonding electrons: 8 (the 6 from the triple bond and 2 from the bond to hydrogen)
Using the formal charge formula:
Formal Charge of Carbon = 4 – (0 + 0.5 × 8) = 4 – 4 = 0
Hence, the formal charge for each carbon atom in C2H2 is 0. This indicates a stable structure with no overall charge in the molecule.