Write the Lewis structure for ethanol (CH3CH2OH), the alcohol found in alcoholic beverages, then answer the following questions: 1. How many valence electrons does this alcohol have? 2. How many bonded electrons does this alcohol have? 3. How many lone pairs of electrons does this alcohol have? 4. How many single bonds does this alcohol have?
The Correct Answer and Explanation is :
Let’s first draw the Lewis structure for ethanol (CH3CH2OH):
- Step 1: Determine the total number of valence electrons.
- Carbon (C) is in Group 14 and has 4 valence electrons. Ethanol has two carbon atoms, so that gives (2 \times 4 = 8) valence electrons.
- Hydrogen (H) is in Group 1 and has 1 valence electron. There are 6 hydrogen atoms in ethanol (3 from the CH3 group and 2 from the CH2 group, plus 1 from the OH group), so that gives (6 \times 1 = 6) valence electrons.
- Oxygen (O) is in Group 16 and has 6 valence electrons. Ethanol has one oxygen atom, so that gives 6 valence electrons. Total valence electrons = (8 \, (\text{from C}) + 6 \, (\text{from H}) + 6 \, (\text{from O}) = 20 \, \text{valence electrons}).
- Step 2: Draw the structure. Connect the atoms as follows:
- The two carbon atoms are connected by a single bond (C-C).
- Each carbon atom bonds with enough hydrogen atoms to fill its valence shell (4 electrons). This gives three hydrogens attached to the first carbon (CH3) and two hydrogens attached to the second carbon (CH2).
- The second carbon is also bonded to a hydroxyl group (OH), where oxygen has a lone pair and forms a single bond with hydrogen.
- Step 3: Distribute the remaining electrons. Place any leftover electrons as lone pairs on the oxygen atom, ensuring each atom fulfills its octet rule, if possible.
Answers to the questions:
- Valence Electrons: Ethanol has a total of 20 valence electrons.
- Bonded Electrons: The 10 bonds (C-C, C-H, O-H) contribute 20 electrons. These are the bonded electrons.
- Lone Pairs: Oxygen has two lone pairs of electrons in the ethanol molecule.
- Single Bonds: Ethanol has 7 single bonds in total:
- 1 between the two carbon atoms (C-C).
- 3 between the carbon and hydrogen atoms (C-H).
- 1 between the carbon and the oxygen atom (C-O).
- 1 between the oxygen and the hydrogen atom (O-H).
Explanation:
In the ethanol molecule, the carbon atoms each form four bonds to fill their octets, the oxygen atom forms two bonds to satisfy its octet, and the hydrogen atoms each form one bond with another atom. The remaining electrons are placed as lone pairs, ensuring that each atom has a stable electron configuration, especially oxygen, which needs two lone pairs to complete its octet. The bonds contribute to the structure’s stability, with single bonds being the most common bond type in ethanol’s structure.