Pure water is a com-pound made from hydrogen and oxygen, but tap water is a mixture, for there are always various substances dissolved in it. Electron shells Electrons spin round the nucleus in different layers or shells. There is a limit to the number of electrons that can fit in each shell. Just how easily the atom interacts with others depends on how full or empty the outer shells are. Hydrogen with one electron in the first shell, is very reactive.
Carbon is the basic chemical of life.
With four electrons in its outer shell, it has four vacancies to form a huge variety of compounds. Oxygen is in the air we breathe. With six out of a possible eight electrons in its outer shell, it will combine with two hydrogen atoms to form water. Since then, however, scientists have discovered many more types as a result of experiments involving smashing atoms to pieces. In addition to this it has been established that every particle has an anti-particle associated with it, which is essentially its mirror image, though every bit as real.