Here's why:
* Oxygen is more electronegative: Oxygen has a stronger pull on electrons than hydrogen. This means the shared electrons in the O-H bonds spend more time closer to the oxygen atom.
* Uneven charge distribution: The oxygen atom ends up with a slightly negative charge (δ-) because it has a higher electron density. The hydrogen atoms, having lost some electron density, become slightly positive (δ+).
* Dipole moment: This uneven distribution of charge creates a dipole moment, with the positive end pointing towards the hydrogen atoms and the negative end pointing towards the oxygen atom.
This polarity allows water molecules to form hydrogen bonds with each other and with other polar molecules, which is crucial for many of its properties, like its high boiling point, surface tension, and ability to dissolve many substances.
