Consider methanol, CH3OH.
a) ?Draw a Lewis dot structure for CH3OH.
b) ?Characterize the bonding within CH3OH, ?e.g. ?nonpolar covalent, polar covalent
c) ?What is the molecular geometry around carbon in CH3OH ? ?Around oxygen?
d) ?Is CH3OH ?polar or nonpolar?
The Correct Answer and Explanation is :
a) Lewis Dot Structure for CH₃OH
The Lewis structure for methanol (CH₃OH) is:
H
|
H - C - O - H
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H- Carbon (C) forms four single covalent bonds: three with hydrogen (H) atoms and one with the oxygen (O) atom.
- Oxygen forms two single bonds: one with the carbon and one with a hydrogen atom, and it has two lone pairs of electrons.
b) Bond Characterization in CH₃OH
- C-H Bonds: These are nonpolar covalent bonds because the electronegativity difference between carbon (2.55) and hydrogen (2.20) is small (~0.35).
- C-O Bond: This is a polar covalent bond because oxygen (3.44) is significantly more electronegative than carbon, creating a partial negative charge on oxygen and a partial positive charge on carbon.
- O-H Bond: This is also a polar covalent bond because oxygen is more electronegative than hydrogen.
c) Molecular Geometry
- Around Carbon: The geometry is tetrahedral due to the four electron groups (three hydrogens and one oxygen) around the carbon atom, with bond angles close to 109.5°.
- Around Oxygen: The geometry is bent or angular because of the two bonding pairs (O-H and C-O) and two lone pairs on oxygen. The bond angle is slightly less than 109.5° due to lone pair repulsion.
d) Polarity of CH₃OH
Methanol (CH₃OH) is polar.
Explanation:
The molecule’s overall polarity arises from its asymmetric distribution of electron density:
- The C-O and O-H bonds are highly polar, creating regions of partial positive (H) and partial negative (O) charges.
- The tetrahedral geometry around the carbon ensures that the polar bonds do not cancel each other out.
- The oxygen atom, with its lone pairs and polar bonds, exerts a significant dipole moment, pulling electron density towards itself.
In addition to bond polarity, the molecular shape contributes to the net dipole moment, making CH₃OH polar. This polarity makes methanol highly soluble in water and capable of forming hydrogen bonds.