Write a Lewis structure for methyl bromide, CH3Br, showing all valence electrons. • You do not have to consider stereochemistry. Explicitly draw all H atoms. • Include all valence lone pairs in your answer. . C P opy uste ? ChemDoodle
The correct answer and explanation is:
To draw the Lewis structure for methyl bromide (CH₃Br), we follow several steps based on the principles of valence electrons, bonding, and the octet rule.
Step 1: Count the Valence Electrons
Each element in the molecule contributes valence electrons as follows:
- Carbon (C): 4 valence electrons (Group 14 element).
- Hydrogen (H): 1 valence electron per atom (Group 1 elements). There are 3 hydrogen atoms, so 3 electrons.
- Bromine (Br): 7 valence electrons (Group 17 element).
Total valence electrons = 4 (from C) + 3 (from H) + 7 (from Br) = 14 valence electrons.
Step 2: Determine the Bonding
- Carbon (C) is the central atom in CH₃Br, as it can form four bonds.
- Hydrogen (H) atoms will bond to carbon, as hydrogen can form only one bond.
- Bromine (Br) will bond with carbon, as bromine can form one bond and has three lone pairs of electrons left after bonding.
Step 3: Construct the Skeleton Structure
- Place carbon in the center, surrounded by three hydrogen atoms (forming single bonds).
- Attach bromine to the carbon atom, also forming a single bond.
Step 4: Distribute Electrons to Satisfy the Octet Rule
- Each carbon (C) atom needs 4 electrons to complete its octet. The three single bonds to hydrogen atoms each contribute one electron, totaling 3 electrons. The bond between carbon and bromine contributes 1 more electron, fulfilling carbon’s octet.
- Each hydrogen atom satisfies its duet rule by sharing one electron with carbon.
- Bromine, as a Group 17 element, starts with 7 valence electrons and forms one bond with carbon. This uses 1 of its electrons, leaving 6 electrons. These 6 remaining electrons form three lone pairs around bromine.
Step 5: Check for the Correct Number of Electrons
The total number of electrons used in bonds and lone pairs should add up to 14. Here’s how it looks:
- Carbon forms 4 bonds (one with each of the 3 hydrogens and one with bromine).
- Each hydrogen has 2 electrons in its bond with carbon.
- Bromine has 6 electrons in lone pairs and 1 electron in the bond with carbon.
Thus, the total count of valence electrons matches our initial calculation of 14.
Final Lewis Structure:
H
|
H - C - Br
|
H
- Carbon has a single bond with each hydrogen and bromine.
- Each hydrogen has 2 electrons (1 shared in the bond with carbon).
- Bromine has three lone pairs (6 electrons) and a single bond with carbon.
In summary, the Lewis structure for CH₃Br consists of carbon (C) at the center, bonded to three hydrogens (H) and one bromine (Br), with all valence electrons correctly placed around the atoms. Carbon follows the octet rule, hydrogen follows the duet rule, and bromine has a complete octet with lone pairs.