Water

Oxygen has six valence electrons. Two pair up with hydrogens to make two O–H bonds, and the remaining four stay on oxygen as two lone pairs. Again there are four electron groups around the central atom, so oxygen is treated as sp³ hybridized, with the four groups pointing roughly toward the corners of a tetrahedron.

With atoms at the end of only two of those four directions, the molecule is bent. It’s not a straight line, even though the formula H₂O might suggest one. Rotate the model to look at it face-on and you’ll see the V shape.

Two lone pairs squeeze the bonds together even more than ammonia’s one lone pair does. The measured H–O–H angle is about 104.5°, smaller than ammonia’s 107° and methane’s 109.5°. Turn on Angles & lengths to see the computed value. Methane, ammonia and water are a neat series: same four electron groups, with 0, 1 and 2 of them lone pairs.

The bent shape matters a lot. Because oxygen pulls electrons toward itself and the molecule isn’t symmetric, water has a positive end and a negative end. That’s why water molecules stick to each other so strongly and why water dissolves so many things.