This chapter looks at several types of molecules to see how differences in their nature (shapes and atoms that make them up) influence chemical processes. First alcohols are introduced. An alcohol is an organic molecule that contains a particular type of chemical group. An alcohol can be a relatively small molecule, such as ethyl alcohol, which chemists usually call ethanol. Ethanol is the alcohol in beer, wine, and liquor. However, large, important biological molecules, such as cholesterol, are also alcohols. Why ethanol dissolves in water, how it can turn into vinegar, and an outline of the chemical reactions in your body that makes methanol (wood alcohol) poisonous but ethanol safe, are presented. Water is discussed, and the properties of water that make life possible are described. Building on the mechanism that enables some molecules to dissolve in water, the molecular structure of soap and oil molecules are examined to see why you need soap to take grease off your dishes and get it to wash down the drain.