Draw the Lewis structure for bromoethane C2H5Br . Be certain you include any lone pairs.
The Correct Answer and Explanation is:
Lewis Structure for Bromoethane (C₂H₅Br):
To draw the Lewis structure of bromoethane, follow these steps:
1. Count total valence electrons:
- Carbon (C): 4 valence electrons × 2 = 8
- Hydrogen (H): 1 valence electron × 5 = 5
- Bromine (Br): 7 valence electrons × 1 = 7
Total valence electrons = 8 + 5 + 7 = 20 electrons
2. Draw the skeletal structure:
Bromoethane has two carbon atoms connected in a chain, with five hydrogen atoms and one bromine atom bonded to them. The general structure is:
H H H
| | |
H — C — C — Br
|
H
3. Add bonds and distribute electrons:
- Each single bond (C–H, C–C, C–Br) = 2 electrons
- Use single bonds to connect:
- The two carbon atoms (C–C)
- Each carbon to enough hydrogens (3 H on the first C, 2 H on the second C)
- The second carbon to the bromine atom
This uses:
6 bonds × 2 electrons = 12 electrons
Remaining electrons: 20 – 12 = 8 electrons
4. Add lone pairs to satisfy octet:
- Hydrogen already has 2 electrons (full).
- Each carbon has 8 electrons (via bonds).
- Bromine needs 6 electrons (3 lone pairs) to complete its octet:
- Br is single-bonded to C and has 3 lone pairs (6 electrons).
- This uses all 8 remaining electrons.
Final Lewis Structure:
H H H
| | |
H — C — C — Br
| ..
H ..
..
- Br has 3 lone pairs (shown as dots).
- All atoms obey the octet/duet rule.
- This is the correct and complete Lewis structure for bromoethane (C₂H₅Br).
Explanation
The Lewis structure of bromoethane (C₂H₅Br) represents the bonding and lone electron pairs in the molecule. The compound consists of two carbon atoms, five hydrogen atoms, and one bromine atom. In organic compounds like alkanes and haloalkanes, carbon atoms typically form four single covalent bonds to satisfy their octet requirement.
In bromoethane, the two carbon atoms are bonded together, forming the ethane backbone. One of these carbon atoms (a primary carbon) is bonded to three hydrogen atoms, while the second carbon is bonded to two hydrogen atoms and a bromine atom. Each hydrogen forms a single covalent bond, requiring only two electrons, which are easily provided by bonding with carbon.
Bromine, being a halogen, has seven valence electrons and typically forms one single bond to achieve a stable octet. In this structure, bromine forms a single bond with the second carbon and retains three lone pairs (six electrons). This allows bromine to reach an octet: two electrons from the C–Br bond and six from its lone pairs.
The Lewis structure uses 20 valence electrons total. Twelve are used to form bonds (six bonds × 2 electrons), and the remaining eight electrons are placed as lone pairs on the bromine atom. This ensures all atoms fulfill the octet rule (except hydrogen, which follows the duet rule).
The correct Lewis structure gives insight into the molecule’s shape and potential reactivity. Bromoethane is a polar molecule due to the electronegativity difference between carbon and bromine, making it an important compound in organic synthesis and substitution reactions.
