These molecules have no permanent overall electrical charge on them but do have small electrical charges at different points. For example water (H20) consists of two hydrogen atoms and an oxygen atom; the hydrogen atoms have a small positive charge and the oxygen atom has a small negative charge (Figure 1.2). The small positive and negative charges attract each other in a similar way to which the north and south poles on a magnet will attract each other. This attraction causes weak bonds to be set up between molecules.

Figure 1.2: The water molecule. Ethanol (CH3CH2OH, the alcohol that gets you drunk) is another example of a polar molecule. It contains 2 carbon atoms 6 hydrogen atoms and 1 oxygen atom (Figure 1.3). Note that the ethanol molecule has a polar part (the alcohol group) and a non-polar part (the rest of the molecule). Whenever you see oxygen in an organic molecule you can assume it to be polar (or at least the part of it that contains the oxygen atoms). See Appendix A5 for other important oxygen containing groups.

Figure 1.3: The ethanol (CH3CH2OH) molecules.

Ethanol is not the only alcohol. Any molecule that contains C and H atoms and one or more -OH groups is an alcohol. For example CH3OH is called methanol and CH3CH2CH2CH2OH is called butanol.

Planet Beer Recipes

1.1.2. Polar Molecules