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julia999's avatar

Using H2O, how can I explain the difference between intramolecular and intermolecular forces?

Asked by julia999 (343points) June 14th, 2009

I’m looking ahead in my Chemistry book and found the question, and I was unsure how to explain it.

I know it has to do with hydrogen bonding between molecules (inter), but what about dipole-dipole?
And within a water molecule, are there hydrogen bonds or electrostatic forces of attraction between the hydrogen-oxygen (polarised) bonds?

I’ve studied for this and had understood it but I accidentally confused myself, so I’d deeply appreciate an answer for this!

NOTE: judging by differences in melting temperatures, I assume the intramolecular forces (whatever they may be) would be stronger?

Thanks in advance :D

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3 Answers

shrubbery's avatar

H2O is a polar covalent molecule. Polar covalent molecules occur when heterogeneous molecules occur between atoms of different electro-negativity (E.N.), which is a measure of how strongly an atom attracts a shared pair of electrons in a bond.
For example the E.N. of H is 2.1 and the E.N of O is 3.5 so in H2O, O is slightly negative relative to H and H are slightly positive, relative to O. Therefore the electron clouds are not symmetrical and electrons are attracted more to O.
Here is a picture.
Opposite ends of a dipole attract by electrostatic attraction. Electrostatic attraction between adjacent molecules is a physical, not chemical property. Polarity affects forces between molecules. The more polar molecules are, the harder they are to separate. This affects the melting and boiling points of molecular substances.
See this picture. H2O is more polar, so attraction between H2O molecules is stronger (bigger δ+ and δ- charges). Because H2O is very polar, these forces are strong and H2O is a liquid at room temperature, while H2S is not.
See this picture. The bonds between H2O molecules are hydrogen bonds. Not a chemical bond, but a strong attraction between the H atom δ+ dipole of molecule and the δ- dipole (in this case O) of an adjacent molecule.

Hope that helps.

westy81585's avatar

Hahahaha, I remember this SAME question from freshmen chemistry…..

Ivan's avatar

Simple answer:

Intramolecular: Bond between Hydrogen and Oxygen atoms within each molecule
Intermolecular: Hydrogen “bonding” between distinct water molecules due to their polarity.

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