Showing your work, draw the Lewis structure of fluoromethane, CH3F, showing all bonding and non-bonding valence electrons, dipole vectors, and partial charges.
The Correct Answer and Explanation is:
Lewis Structure of Fluoromethane (CH₃F)
To draw the Lewis structure of fluoromethane (CH₃F), follow these steps:
1. Count the total number of valence electrons:
- Carbon (C): 4 valence electrons
- Hydrogen (H): 1 valence electron × 3 = 3
- Fluorine (F): 7 valence electrons
- Total = 4 + 3 + 7 = 14 valence electrons
2. Determine the central atom:
Carbon is the central atom because it can form 4 bonds.
3. Connect atoms with single bonds:
- Carbon forms three single bonds with three hydrogen atoms.
- Carbon forms one single bond with fluorine.
That’s a total of 4 single bonds (4 × 2 = 8 electrons used).
4. Distribute remaining electrons:
We’ve used 8 of 14 electrons → 6 electrons left.
These go to fluorine as 3 lone pairs (6 electrons) to complete its octet.
5. Check octets:
- Carbon has 4 bonds = 8 electrons → satisfies octet.
- Hydrogens each have 1 bond = 2 electrons → satisfied.
- Fluorine has 1 bond + 3 lone pairs = 8 electrons → satisfied.
Lewis Structure:
H
|
H — C — F
|
H
..
:
.. ← 3 lone pairs on fluorine
Dipole Vectors and Partial Charges:
- Fluorine is highly electronegative, pulling electron density towards itself.
- This results in a dipole moment pointing from carbon to fluorine.
- Partial charges:
- Fluorine: δ⁻
- Carbon: δ⁺
- Hydrogens: slightly positive or neutral
Dipole vector: → (arrow pointing from carbon toward fluorine)
Explanation (300+ words):
Fluoromethane (CH₃F) is a simple organic molecule consisting of one carbon atom bonded to three hydrogen atoms and one fluorine atom. When drawing the Lewis structure, the total valence electrons are determined first. Carbon has 4 valence electrons, each hydrogen has 1, and fluorine has 7, summing to 14 valence electrons.
Carbon, being tetravalent, sits at the center and forms four sigma (σ) bonds: one with each of the three hydrogens and one with fluorine. Each bond consumes 2 electrons, so 8 electrons are used in bonding. The remaining 6 electrons are placed as three lone pairs on the fluorine atom, as it requires a full octet.
This Lewis structure shows all valence electrons: bonding electrons between atoms and non-bonding (lone pairs) on fluorine. Each hydrogen has a complete outer shell with 2 electrons. Carbon achieves an octet via four bonds. Fluorine has one bonding pair and three lone pairs, making 8 electrons around it.
The polarity of fluoromethane is a key feature. Fluorine is the most electronegative element, significantly more than carbon or hydrogen. As a result, the shared electrons in the C–F bond are pulled closer to fluorine, creating a partial negative charge (δ⁻) on fluorine and a partial positive charge (δ⁺) on carbon. This uneven electron distribution leads to a molecular dipole. The dipole arrow points from the less electronegative atom (carbon) to the more electronegative one (fluorine).
Because of this strong dipole and the presence of polar bonds, fluoromethane is a polar molecule, which affects its physical properties, such as boiling point and solubility. Its structure and polarity make it an important molecule in organic and atmospheric chemistry.