A compound is a substance that contains atoms of two or more different elements, chemically joined together. For example, water is a compound of hydrogen and oxygen, chemically joined together.

The table shows some examples: Notice that the different substances in a mixture can be single atoms, molecules of elements or molecules of compounds.

An entirely new class of super-reactive chemical compounds has been discovered under atmospheric conditions. Researchers have documented the formation of so-called trioxides -- an extremely ...