Atoms, Elements, Compounds the time the Curies discovered
polonium and radium, identifying new chemical elements was one
of the highest goals a scientist could hope to reach. A chemical
element is a substance that contains only one kind of atom. If
you keep dividing up such a substance, you finally get to the
tiny atoms. Nobody had been able to divide an atom further, into
smaller pieces. in the world around us is made up of the atoms
of the chemical elements, combined with one another in countless
ways in compounds. For example, water is not an element but a
compound of two true elements, hydrogen and oxygen. When
chemists describe water as H2O they mean that the smallest
particle of water is made of two atoms of hydrogen and one atom
of oxygen. For scientists of Marie Curies time, it was a great
mystery why atoms of different elements had different chemical
propertiesfor example, why it was in the nature of oxygen atoms
to combine in this way with hydrogen to make a wet liquid.
Experiments using radioactivi