The Water molecule - rotatable in 3 dimensions

This shows a single molecule of water. We all know that water has the formula H₂O.

Each hydrogen shares an electron with oxygen and this forms a pair of covalent bonds, but the hydrogen atoms are not attached to oxygen in a straight line.
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This electron sharing means that each hydrogen has a total of 2 electrons in the outer shell which stabilises them , and oxygen has a total of 8 electrons, which stabilises it . But the remaining non-bonding electrons form two lone pairs, which space themselves (in 3 dimensions) away from the bonds with hydrogen.

In accordance with valence shell electron pair repulsion (VSEPR) theory, these and the hydrogen-oxygen bonds should project outwards as if to the corners of a regular tetrahedron (109.5°), but the non-bonding electrons are effectively closer to the oxygen nucleus than the shared electrons so the angle between the two hydrogens is usually 104.5°.

Click to hide the above detail about electrons in water
The atomic arrangement means that the water molecule has a partial negative charge (δ-) near the oxygen atom due the unshared pairs of electrons, and partial positive charges (δ+) near the hydrogen atoms. This allows water to form hydrogen bonds (with itself, and other compounds with electronegative atoms) and also explains the special physical and chemical properties of water which are often seen as essential to life.

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