Science
What is An isotope?
Isotopes are versions of the same chemical element that have the same number of protons but different numbers of neutrons. They behave almost identically in chemistry, but differ in mass and in whether they are radioactive.
See it, don’t just read it.
Watch a 2-minute lesson with voice + animation that explains an isotope.
Key things to understand
- 1Same element, same protons — but a different neutron count, so a different mass.
- 2For example, carbon-12 and carbon-14 are both still carbon.
- 3Some isotopes are stable; others are radioactive and decay over time.
- 4Radioactive isotopes power carbon dating and medical imaging.
- 5Chemically they react the same, because chemistry depends on electrons, not neutrons.
Frequently asked questions
- What's the difference between isotopes of an element?
- Only the number of neutrons, which changes the atom's mass but not its chemical identity.
- What is a radioactive isotope?
- An unstable isotope whose nucleus decays over time, emitting radiation — useful for dating, imaging, and energy.
- How is carbon-14 used?
- It decays at a known rate, so the amount left in ancient organic material reveals its age (radiocarbon dating).