What is the role of hydrogen bonds in holding water molecules together?

In summary, hydrogen bonds involve the interaction between a hydrogen atom and an electronegative atom from a different molecule, leading to intermolecular forces. Intramolecular forces, on the other hand, occur within a single molecule. Hydrogen bonding can be classified as either intermolecular or intramolecular, depending on the context. However, in the case of water, the bonding between hydrogen and oxygen is an example of intramolecular force, as the atoms are within the same molecule. This distinction is important to understand the concept of hydrogen bonds, especially in the context of larger molecules such as proteins.
  • #1
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I'm a little confused on hydrogen bonds. Here's a sample question and answer I'm having trouble with:1) In a single molecule of water, two hydrogen atoms are bonded to a single oxygen atom by
A) hydrogen bonds.
B) nonpolar covalent bonds.
C) polar covalent bonds.
D) ionic bonds.
E) van der Waals interactions.
Answer: C

OK - polar covalent bonds are holding the hydrogen atoms to the oxygen atom. That I can understand.

But couldn't the interaction between the hydrogen and the oxygen also be classified as a hydrogen bond? Hydrogen bond, as I was taught in Chem, is simply the interaction between H and F, O, or N. So couldn't the answer also be A?
 
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  • #2
Hydrogen bonding is the interaction of a hydrogen atom with an electronegative atom that comes from a different molecule (or functional group if you're dealing with a large molecule). There's (typically) a clear cut donor and acceptor - for example, in liquid water, the intramolecular OH bond length is one-half the typical hydrogen bond length between water molecules. But if they're both hydrogen bonding - to go with your proposed redefinition - why are they so different, then?
 
  • #3
No because Hydrogen bonding is a form of intermolecular force - forces which occur between molecules. The bonding of hydrogen and oxygen in water is an example of intramolecular force - the force within a molecule.
 
  • #4
Hydrogen bonds, according to the IUPAC Gold Book, can be an intramolecular force.

http://goldbook.iupac.org/H02899.html

IUPAC Gold Book said:
Hydrogen bonds may be inter-molecular or intramolecular.
 
  • #5
That is what I was attempting to (imperfectly, it seems) convey - for example, if you have a very large molecule such as a protein, the amide proton of residue i can hydrogen bond to to the carbonyl oxygen of residue i-4. However, that hydrogen is going to be - on average - closer to one of the atoms than the other.

If you need further clarification, just ask. But I think the protein example is the best way to understand what is meant by an intramolecular hydrogen bond.

P.S. - When I said "intramolecular OH bond length," I was referring to the bond lengths *within* the water molecule, not the distances between hydrogen bonded atoms. Perhaps that wasn't clear - sorry about that.
 
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FAQ: What is the role of hydrogen bonds in holding water molecules together?

What is a hydrogen bond?

A hydrogen bond is a type of weak chemical bond that occurs between a hydrogen atom and an electronegative atom, such as oxygen or nitrogen. It is responsible for the unique properties of water, such as its high boiling point and surface tension.

How does hydrogen bonding contribute to the structure of water?

Hydrogen bonding causes the water molecules to arrange themselves in a specific way, with the oxygen atoms slightly negative and the hydrogen atoms slightly positive. This results in the formation of a tetrahedral structure, where each water molecule is bonded to four others.

What is the significance of hydrogen bonds in biological processes?

Hydrogen bonds play a crucial role in various biological processes, such as protein folding, DNA replication, and enzyme activity. They help to stabilize the structures of biomolecules and facilitate important interactions between molecules.

How does the strength of a hydrogen bond compare to other types of chemical bonds?

Hydrogen bonds are weaker than covalent or ionic bonds, but they are stronger than intermolecular forces, such as van der Waals forces. They are strong enough to give water its unique properties, but weak enough to allow molecules to easily break and reform these bonds.

What factors affect the strength of a hydrogen bond?

The strength of a hydrogen bond is influenced by several factors, such as the distance between the hydrogen and electronegative atoms, the angle of the bond, and the polarity of the atoms involved. Additionally, the presence of other molecules or ions can also affect the strength of hydrogen bonding in water.

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