We have only to look around us to recognize that our world is not a world of hydrogen and helium. The chemistry in the first two chapters is quite inadequate for dealing with our corner of the universe. For this, we need to understand the heavier elements, which have more protons in their nuclei and more electrons around them. As was mentioned in Chapter 2, the innermost shell of any atom can hold a maximum of two electrons, and the second shell can hold eight electrons.

We can build up a series of ten atoms with increasing numbers of electrons, before we run out of room in the first two electron shells. The next three chapters are devoted to these simplest ten atoms. With them, we can outline the chemistry of our world, although the heavier elements will be necessary to fill in the details. These ten elements are the atoms of life, for they make up 99.35 % of the material in any living organism.