Q. \( \)Lewis structure of \( \mathrm{C_2H_6O} \).

Chemistry Tutor Solution: Lewis Structure of \( \mathrm{C_2H_6O} \)

First, we identify what \( \mathrm{C_2H_6O} \) represents. This molecular formula can correspond to more than one structural (connectivity) possibility, but the Lewis structure question usually expects you to draw the common structural forms. For many “Lewis structure of \( \mathrm{C_2H_6O} \)” problems, the expected answers are the two constitutional isomers:

\( \mathrm{CH_3-O-CH_3} \) (dimethyl ether) and \( \mathrm{CH_3-CH_2-OH} \) (ethanol). Each has a different Lewis structure.

Step 1: Count Total Valence Electrons

Lewis structures use only valence electrons.

Valence electrons for each atom:

• Carbon (C) has 4 valence electrons
• Hydrogen (H) has 1 valence electron
• Oxygen (O) has 6 valence electrons

In \( \mathrm{C_2H_6O} \):

\[
\text{Total valence electrons} = 2(4) + 6(1) + 1(6)
\]

\[
= 8 + 6 + 6 = 20
\]

So, the Lewis structure must use 20 total valence electrons.

Step 2: Decide the Connectivity (Isomer Options)

There are two common ways to connect the atoms while satisfying typical bonding patterns:

• Dimethyl ether: \( \mathrm{CH_3-O-CH_3} \)
• Ethanol: \( \mathrm{CH_3-CH_2-OH} \)

Below are both Lewis structures.

Lewis Structure 1: Dimethyl Ether \( \mathrm{CH_3-O-CH_3} \)

Step 3: Choose a Skeletal Bonding Pattern

Connect an oxygen between two carbons. Each carbon is bonded to three hydrogens and to oxygen.

Skeleton:

\( \mathrm{C – O – C} \), with each carbon also bonded to three H’s.

Bond count in this structure:

• Two \( \mathrm{C-H} \) sets: \( 6 \) single bonds total
• Two \( \mathrm{C-O} \) single bonds

Total single bonds = \( 8 \).

Single bonds use electrons in pairs, so the electrons needed for all single bonds are:

\[
8 \text{ bonds} \times 2 \text{ electrons per bond} = 16
\]

We had 20 valence electrons total, so remaining electrons:

\[
20 – 16 = 4
\]

Step 4: Place Remaining Electrons as Lone Pairs

Those 4 remaining electrons go on the oxygen as two lone pairs (oxygen usually has 2 lone pairs in ethers).

Each lone pair is 2 electrons, so 4 electrons makes 2 lone pairs.

Step 5: Write the Final Lewis Structure (with Lone Pairs)

Key features:

• Oxygen has two lone pairs
• All atoms have appropriate valence satisfaction

Lewis structure (text depiction):

\( \mathrm{H_3C – O – CH_3} \) with oxygen having two lone pairs.

Using expanded form:

\( \mathrm{H_3C} \) bonded to oxygen, oxygen bonded to \( \mathrm{CH_3} \), and oxygen has two lone pairs.

Lewis Structure 2: Ethanol \( \mathrm{CH_3-CH_2-OH} \)

Step 6: Choose a Skeletal Bonding Pattern

In ethanol, oxygen is terminal and bonded to one carbon and one hydrogen.

Skeleton:

\( \mathrm{C – C – O – H} \)

Count single bonds:

• \( \mathrm{C-C} \): 1 bond
• \( \mathrm{C-H} \): \( 5 \) bonds on the two carbons total (three on \( \mathrm{CH_3} \) and two on the \( \mathrm{CH_2} \))
• \( \mathrm{C-O} \): 1 bond
• \( \mathrm{O-H} \): 1 bond

Total single bonds = \( 1 + 5 + 1 + 1 = 8 \) bonds.

Electrons used for 8 single bonds:

\[
8 \times 2 = 16
\]

Remaining electrons:

\[
20 – 16 = 4
\]

Step 7: Place Remaining Electrons as Lone Pairs on Oxygen

Those 4 electrons form two lone pairs on oxygen.

Step 8: Write the Final Lewis Structure (with Lone Pairs)

Key features:

• Oxygen has two lone pairs
• Oxygen is bonded to one carbon and one hydrogen
• All tetravalent carbons and monovalent hydrogens satisfy typical valence

Lewis structure (text depiction):

\( \mathrm{CH_3-CH_2-OH} \) with oxygen having two lone pairs.

Final Answer (What You Should Draw)

The Lewis structure of \( \mathrm{C_2H_6O} \) is not unique; the two most common constitutional isomers are:

• Dimethyl ether: \( \mathrm{CH_3-O-CH_3} \), oxygen with two lone pairs
• Ethanol: \( \mathrm{CH_3-CH_2-OH} \), oxygen with two lone pairs