The world around us includes all sorts of "thing"—from air, water and soil to living organisms like ourselves. These "things" are so numerous as to be impossible to count, and between them make up an incredibly complex world. What is interesting, however, is that only a little over 100 kinds of elements can exist in our world at all. And because 10 of these kinds of elements disappear the moment they are created, all the material things we know—air, our houses and our bodies—are made from just 92 to 93 elements. The units of elements are atoms, and those atoms, measuring just fractions of a nanometer across, join together in myriad combinations to create substances with various properties, such as the ability to conduct electricity, react powerfully with other substances or carry energy. In short, the complex world of which we are a part is formed through the combination of just a hundred or so different kinds of atoms.