Final answer:
Isotopes are different forms of the same element with the same number of protons but a different number of neutrons. Carbon has three isotopes: carbon-12, carbon-13, and carbon-14. Carbon-14 is a radioactive isotope.
Step-by-step explanation:
Isotopes are different forms of the same element that have the same number of protons, but a different number of neutrons.
For example, a typical carbon atom on the periodic table of elements should have six protons and six neutrons in its nucleus, called carbon-12.
Some atoms of carbon can have an extra neutron in the nucleus, called carbon-13, and some can have two extra neutrons in the nucleus, called carbon-14.
If an atom has too many neutrons in its nucleus, it can become unstable because the nucleus has too much energy; this is called a radioactive isotope. Carbon-14 is a radioactive isotope.
Just as the periodic table of elements summarizes the most important information of every element, there are periodic tables of isotopes that include all the possible isotopes for each element and their relative abundance and properties.