In chemistry, isotopes are atoms of the same element that have the same number of protons in their nucleus but different numbers of neutrons. This means that isotopes of the same element have the same atomic number, but different atomic masses.
For example, carbon has three naturally occurring isotopes: carbon-12, carbon-13, and carbon-14. Carbon-12 has 6 protons and 6 neutrons in its nucleus, carbon-13 has 6 protons and 7 neutrons, and carbon-14 has 6 protons and 8 neutrons.
Isotopes can have different physical and chemical properties due to their different atomic masses. For example, carbon-14 is radioactive and is used in radiocarbon dating, while carbon-12 and carbon-13 are stable and are commonly used in organic chemistry and other fields.