When you draw the Lewis Structure for CH3OCH2CH3, what is the total number of lone pair electrons? A 0 B 3 C 4 D 2 E 1
The Correct Answer and Explanation is:
The correct answer is: C) 4
Explanation:
The molecule CH₃OCH₂CH₃ is called ethyl methyl ether, a common ether. To determine the number of lone pair electrons in the Lewis structure, we follow these steps:
Step 1: Count total valence electrons
- Carbon (C): 4 valence electrons × 3 = 12
- Hydrogen (H): 1 valence electron × 8 = 8
- Oxygen (O): 6 valence electrons × 1 = 6
Total valence electrons = 12 + 8 + 6 = 26 electrons
Step 2: Build the molecular skeleton
The structure of CH₃OCH₂CH₃ is:
CH3—O—CH2—CH3
- A methyl group (CH₃) is bonded to an oxygen atom.
- The oxygen is also bonded to an ethyl group (CH₂CH₃).
Step 3: Assign bonds and lone pairs
- Bonds:
- Each single bond accounts for 2 electrons.
- There are:
- 8 single bonds involving H–C (3 in CH₃, 2 in CH₂, 3 in CH₃): 8 bonds = 16 electrons
- 2 C–C single bonds = 2 bonds = 4 electrons
- 1 C–O single bond = 1 bond = 2 electrons
- Total bonding electrons = 16 + 4 + 2 = 22 electrons
- Remaining electrons:
- Total valence electrons: 26
- Used in bonds: 22
- Remaining: 4 electrons
These remaining 4 electrons are placed as lone pairs on the oxygen atom, since all other atoms (C, H) are satisfied with their bonds.
- Oxygen needs 8 electrons to complete its octet.
- It has 2 bonds (to C atoms), totaling 4 shared electrons.
- It needs 4 more electrons → 2 lone pairs → 4 lone pair electrons.
Final Result:
Only the oxygen atom contributes 1 pair + 1 pair = 2 lone pairs = 4 lone pair electrons.
Answer: C) 4
