How can something so small generate so much energy? The secret is in the basic building block of all matter - the atom. All matter in the universe is made up of atoms, particles so tiny that they cannot be observed even under a microscope.
Atoms
The atom resembles a miniature solar system. In the centre of the atom is the nucleus around which electrons orbit, like planets moving around the sun. The nucleus, composed of protons and neutrons, contains most of the mass of the atom. Tiny electrons move around in relatively large orbits with nothing in between.
Atoms that contain an equal number of protons and electrons are referred to as elements. There are 90 kinds of naturally occurring elements and at least 14 other artificial elements have been created by scientists in controlled experiments. Elements are listed in a periodic table arranged according to their number of protons (atomic number). For example, an atom of hydrogen, the lightest element, has just one proton in the nucleus. An atom of uranium, the heaviest element found in nature, has 92 protons.
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| Elements are listed in a periodic table arranged according to their number of protons. |
Isotopes
The number of protons in the nucleus of an element is always the same but the number of neutrons may vary. For example, carbon atoms that have six protons usually have six neutrons. However, some have eight. Atoms that have a different number of neutrons than protons are called isotopes. Each isotope is identified by its atomic mass, the sum of its protons and neutrons.
Naturally occurring uranium is made up primarily of two different uranium isotopes. Approximately 99.3% is uranium 238 (U-238) with 92 protons and 146 neutrons, and 0.7% is uranium 235 (U-235). Under certain conditions the nucleus of U-235 can be made to split, or fission. Because of this property, U-235 plays an important role in the creation of nuclear energy.
Source:http://www.cameco.com/uranium_101/fact.php#two
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