How Are Isotope Ratios Formed?

Isotopes

• The way atoms are arranged on the periodic table of elements reflects the different properties of matter. Each atom is assigned an atomic number, which determines its location on the periodic table. For example, the element oxygen has the atomic number 8, meaning it has eight protons at its center. Protons are positively charged particles. The number of neutrons, which are particles at the center of an atom with no charge, are normally the same number as the number of protons. However, isotopes are variations in a particular element's atomic makeup that have a different number of neutrons. There are two kinds of isotopes, stable and radioactive isotopes.

Stable Isotopes

• When an atom forms as an isotope, the number of neutrons it has affects how much mass it has and can thereby alter the properties of the element. Isotopes of an atom may be more or less abundant that the normal form of an atom. Stable isotopes are described as stable because their atomic composition is less likely to decompose in the way radioactive isotopes are prone to do.

Radioactive Isotopes

• There are some elements that form both stable and radioactive isotopes. These isotopes are prone to releasing gamma particles, and they "decay" at a measurable rate. Radioactive decay rate is a property radioactive isotopes have in which they break down at a steady rate over a predictable period of time. This property is useful to scientists, because it allows them to date items such as rocks, bones and pottery fragments from early civilizations or geological events to determine their geological age.

Isotope Ratios

• Biological processes seem to form some elements, such as carbon and sulfur, into isotopes. By measuring the ratio of an isotope in a sample of an element using a technique called mass spectronomy, scientists can tell by the isotope ratio whether the minerals in the sample may have once been part of a living organism. For example, if a scientist analyzes a sample of carbon, he would find that part of the carbon sample is composed of normal carbon and part of the sample contains the carbon isotope Carbon-13. The scientist would write the results in the form of a ratio. If the sample contained 25 percent Carbon-13 and 75 percent Carbon, the ratio would be written 1:4.