Attraction between molecules
Every bond so far has been inside a molecule. Polarity creates a second kind of attraction, one that acts between molecules.
A water molecule has hydrogen atoms carrying a small positive charge and an oxygen atom carrying a small negative one. Put two water molecules next to each other and the hydrogen of one is attracted to the oxygen of the other, exactly as any opposite charges would be.
Intermolecular bond
An attraction arising between one molecule and another, rather than between the atoms within a molecule. Also called an intermolecular force.
Figure to be added
Weaker than the bonds inside
These attractions are real but modest. They are not as strong as the covalent bonds holding the oxygen and hydrogen atoms together within a single water molecule.
| Attraction | Acts between | Strength |
|---|---|---|
| Covalent bond | Atoms inside one molecule | Strong |
| Intermolecular bond | One molecule and the next | Much weaker |
That difference explains something you have seen. Boiling water turns liquid into steam without decomposing it into hydrogen and oxygen: the heat is enough to pull the molecules apart from one another, but nowhere near enough to break the bonds inside them.
Weak does not mean unimportant. These attractions are what decide whether a substance is a gas, a liquid or a solid at room temperature.