What Is An Isotope?

Before we discuss what an isotope is we need to review the basics of what gives an atom its particular properties.

All the atoms of a sample of a pure substance, such as gold, copper, helium and so on, has the same number of protons and electrons. They must do, since it is the protons (+ charges) that attract the electrons (- charge) to that nucleus. This is why in neutral pure substances, the number of protons and electrons is the same for each atom.

The electrons are the outermost part of all atoms, and so when a chemical reaction takes place it happens with the electrons. Therefore all the atoms of a particular element will react the same way with other elements or compounds, since their electron arrangements are all the same.

So...What is an Isotope?

Protons are not the only particles in the nucleus of an atom. There is another component, the neutron. The majority of atoms of an element will have the same number of neutrons in the nucleus. Helium is a good example of this; all Helium atoms have 2 protons and 2 electrons, but the number of neutrons may vary between 1 and 6, or even more. These extra neutrons have NO EFFECT ON THE CHEMICAL PROPERTIES of the atoms but they do affect the weight of the atom. Different numbers of neutrons in the nucleus of an element give the different isotopes.

The most common isotope for any element is also the most stable. In the Helium example, the most stable isotope has two neutrons in its nucleus. All the other variations are not as stable as the 2-neutron variety and will break apart. This process is called nuclear decay and the process not only results in the breakup of the nucleus, but also emits energy. This energy comes in many forms and has the generic name radiation. Atoms whose nuclei decy and emit this radiation are said to be radioactive.