What Are Isotopes?

Isotopes are defined as different forms of an element, each having a different atomic mass. Hydrogen (represented by the chemical symbol H), for instance, is the first element in the periodic table. It has seven isotopes, namely 1H (protium), 2D (deuterium), 3T (tritium, which is a naturally radioactive half-life), 4H (hydrogen-4), 5H (hydrogen-5), 6H (hydrogen-6) and 7H (hydrogen-7). The last four isotopes of hydrogen are unstable half-lives. Protium and deuterium are stable half-lives. All the isotopes of every element have a nucleus of their own. Each of these nuclei contains the same number of protons (the same atomic number), but different numbers of neutrons. Oxygen is represented by the chemical symbol O. It has fifteen isotopes, namely 12O, 13O, 14O, 15O, 16O, 17O, 18O, 19O, 20O, 21O, 22O, 23O, 24O, 25O and 26O. Three of these isotopes, namely 16O, 17O and 18O are stable half-lives, and the remaining 12 isotopes are unstable half-lives.

The number of protons in the atom defines the element. All the atoms of a particular element have the same number of protons in their nuclei; this number is unique to each particular element and is its atomic number.
However, some atoms of the same element can have different numbers of the neutrons: These are called the isotopes of the element.
Because isotopes have the same number of protons and the same electron configuration as the element, they have the same chemical properties, so their reactions are the same. They are easy to spot becasue they have the same atomic number but a different mass number.