2.9:
Isotopes
Isotopes are forms of an element where the number of neutrons in the nucleus varies, but the number of protons — the atomic number — is the same. This results in different atomic masses but does not affect the atom's charge.
All elements have isotopes.
For example, elemental carbon has three naturally occurring isotopes. carbon-12, the most common of them, has six neutrons and six protons. The other two, carbon-13 and carbon-14, have seven and eight neutrons, respectively.
Carbon-12 and 13 are stable under natural conditions and do not decay into other elements over time.
Heavier isotopes, such as carbon-14, have an unstable nucleus and decay into stable products over time by energy emission. These are known as radioactive isotopes.
The decay of radioactive isotopes occurs at a constant rate. The decay is the basis for radiometric dating, a technique used to determine geological age.
2.9:
Isotopes
Elements have a set number of protons that determines their atomic number (Z). For example, all atoms with eight protons are oxygen; however, the number of neutrons can vary for atoms of the same element. The sum of the number of protons and the number of neutrons is the mass number (A). Atoms with the same atomic number but different mass numbers are called isotopes. Elements can have multiple isotopes, for example, carbon-12, carbon-13, and carbon-14.
An element's atomic mass, or weight, is a weighted average of the masses of the element's isotopes. The weighted average reflects the relative abundance of the different isotopes in the sample. In other words, the masses of the most common isotopes contribute most strongly to the average.
Radioactive decay can alter the number of protons in an element, changing its identity. Many elements have stable isotopes, but most have at least one radioactive isotope, known as a radioisotope. Elements with atomic numbers of 84 or higher are all unstable and decay into elements with lower atomic numbers.
Radiation can help determine a material's age and can be used to diagnose and track medical conditions and treat cancer.