Here's why:

* Electron pairs repel each other: The electron pairs around the central atom, including bonding pairs and lone pairs, try to stay as far apart as possible due to their negative charges.

* Two bonded groups: These will be positioned at an angle to minimize repulsion.

* Lone pair: The lone pair takes up more space than a bonding pair, pushing the bonded groups closer together.

This leads to a bent or angular shape with an angle typically less than 109.5 degrees (the ideal tetrahedral angle).

Example: Water (H₂O) has two hydrogen atoms bonded to an oxygen atom and two lone pairs on the oxygen. This gives water its characteristic bent shape.