Worked Example
A molecule's distribution of charge affects its properties in the atmosphere.
Question: Look at the molecules below. Do they have an uneven distribution of positive and negative charge? After you have made a decision you can click on the molecules to check your answer.
Water, H2O
Water, H2O
The oxygen atom is far more electronegative than the two hydrogen atoms. As a result, the oxygen atom tends to hold more negative charge. This negative charge is not evenly spread throughout the molecule. Thus, water has a permanent dipole.
Nitrogen, N2
Nitrogen, N2
Nitrogen does not have an uneven charge distribution because it is a homonuclear diatomic molecule (it is made of two of the same type of atoms). The atoms have identical electronegativities so the charge on the molecule is not shifted.
Ozone, O3
Ozone, O3
Although ozone consists entirely of the same type of atom (three oxygen atoms), the molecule is in a 'bent' configuration, so that the negative charge may not be evenly distributed.
Recognizing uneven charge distributions will be important later as we identify greenhouse gases.