MakeTheBrainHappy: Isotope Notation

Answer: Isotope Notation is a written form of an element which reveals not only its identity but also how many protons, neutrons and electrons it contains. This notation is very useful when you are trying to compare different "isotopes" of an element.

Isotopes are versions of elements which differ in the number of neutrons which they contain. Each version of the atom contain's the same number protons, and if the atom is electrically neutral, the same number of electron. The number of neutrons determines the isotope/mass number of the atom. Many elements have only a certain number of isotopes. Different isotopes vary in how stable they are chemically. For example, hydrogen has three different isotopes, with two being stable and one being unstable. Tritium, shown below, is the unstable isotope of hydrogen which decays.

Elements vary in how many different isotopes they have and the stability of each. For example, technetium has over 50 recorded isotopes with none of them being stable. This is quite different from hydrogen which does have stable isotopes. If you wanted to specify a specific atom of technetium you would also need to specify which of the 50 different types you were speaking of. This is why isotope notation is handy.

The graphic above displays the generic writing of an isotope. The element symbol is displayed to the right in a large font. Two different numbers are displayed to the left of the symbol in smaller font. The bottom number is the atomic number, or the number of protons in the atom. The top number is the mass number, which is the number of protons and neutrons combined. If you have two of the variables in this format, you can derive the third through simple calculations. Here is hydrogen's unstable isotope, tritium, written in isotope notation.