What are Isotopes?
Atoms with the same number of protons but different number of neutrons are called isotopes. We learned in the sections on atoms and elements that each element has its own unique atom made up of a specific number of protons. The number of protons determines the atomic number of the element. Each atom also has the same number of electrons as protons.
What is an Isotopes?
Isotopes are atoms that have the same number of protons and electrons but different numbers of neutrons. Changing the number of neutrons in an atom does not change the element. Atoms of elements with different numbers of neutrons are called “isotopes” of that element.
Naming Isotopes
Since neutrons have no charge, changing the number of neutrons does not affect the chemical properties of the element. However, this changes the mass of the element. Isotopes are defined by their mass, which is the total number of protons and neutrons.
Isotopes are usually written in two ways. Both use the mass of the atom where mass = (number of protons) + (number of neutrons). The first consists of placing the superscript mass before the element’s symbol:
- 4He
- 14C
- 235U
The alternative is to write the element and write the mass after the dash next to the element name:
- helium-4
- carbon-14
- uranium-238
Hydrogen
Hydrogen is the only element for which isotopes are specifically named. The common hydrogen, which does not contain neutrons, is called protium. Hydrogen with one neutron is called deuterium and hydrogen with two neutrons is called tritium.
How many Isotopes can an Element have?
All elements have several isotopes. Hydrogen has the lowest number of isotopes with only three. The elements with the most isotopes are cesium and xenon with 36 known isotopes.
Stable and Unstable Isotopes
Some isotopes are stable and some are unstable. When an isotope is unstable, it decays over time and eventually transforms into another isotope or element. Unstable isotopes are considered radioactive. Most of the elements found in nature are made up of stable isotopes. The element with the most stable isotopes is tin which has ten different stable isotopes.
Interesting Facts about Isotopes
Many elements exist only in unstable or radioactive forms.
All non-natural or man-made elements are radioactive isotopes.
Heavier isotopes tend to react more slowly than lighter isotopes of the same element.
Deuterium (an isotope of hydrogen with neutrons) can form water with oxygen. It is known as “heavy water” because deuterium has twice the mass of normal hydrogen (protium).
There are 254 known stable isotopes and 80 elements with at least one stable isotope.
Twenty-six elements have only one stable isotope. These elements are known as monoisotopes.