If a solid line represents a covalent bond and a dotted line represents intermolecular attraction, which of the choices shows a hydrogen bond?
A. H−H
B. H4C⋅⋅⋅⋅⋅⋅H−F
C. H3N⋅⋅⋅⋅⋅⋅H−O−H
D. H2O⋅⋅⋅⋅⋅⋅H−CH3
The Correct Answer and Explanation is:
The correct choice that represents a hydrogen bond is C. H₃N⋅⋅⋅⋅⋅⋅H−O−H.
Explanation:
Hydrogen bonding is a specific type of intermolecular attraction that occurs when a hydrogen atom covalently bonded to a highly electronegative atom (such as nitrogen, oxygen, or fluorine) experiences an attraction to another electronegative atom. In the context of the choices provided, we need to identify the option that best illustrates this interaction.
- Choice A: H−H
- This represents a single covalent bond between two hydrogen atoms. There is no hydrogen bond here as there is no electronegative atom involved.
- Choice B: H₄C⋅⋅⋅⋅⋅⋅H−F
- Here, we have a covalent bond between carbon and hydrogen, and a dotted line indicates an intermolecular attraction between H₄C (methane) and HF (hydrogen fluoride). However, while HF can form hydrogen bonds, the structure shown does not indicate a hydrogen bond involving hydrogen atoms connected to electronegative atoms. Instead, it is simply an attraction between methane and HF.
- Choice C: H₃N⋅⋅⋅⋅⋅⋅H−O−H
- In this choice, the dotted line indicates a hydrogen bond between the hydrogen atom of the amine group (NH₃) and the oxygen atom of a water molecule (H₂O). The nitrogen atom is less electronegative than oxygen, and thus, when the hydrogen atom from NH₃ is near the oxygen of H₂O, a hydrogen bond can form. This is a classic representation of hydrogen bonding.
- Choice D: H₂O⋅⋅⋅⋅⋅⋅H−CH₃
- Although this choice includes a water molecule, the interaction depicted is between water and a methyl group (CH₃). The bond shown does not constitute a hydrogen bond because CH₃ is not an electronegative atom capable of forming a hydrogen bond.
In summary, choice C illustrates the hydrogen bond between a nitrogen atom bonded to hydrogen and an oxygen atom bonded to hydrogen, both of which are highly electronegative, making this the correct representation of a hydrogen bond.