Science Buddies: "Ask an Expert"

isotopes are defined as having a different number of protons to neutrons, but carbon-12 has the same number yet is an isotope. Why?

Hi ali13456,

Isotopes are forms of the same element with equal numbers of protons but different numbers of neutrons. For example, both carbon-12 and carbon-14 have 6 protons. But carbon-12 has 6 neutrons while carbon-14 has 8 neutrons. By definition, carbon-12, carbon-13 and carbon-14 are all isotopes of the carbon.

I hope this helps. Please post again if you have more questions.

A. Norman

Thanks,
I'm still a little confused.
I thought what defined an isotope was that in the element there are the name number of protons as neutrons, so categorically Carbon-12 is not an isotope.
What is Carbon in its normal form then?

Hi ali13456,

Carbon-12 is the most abundant isotope of carbon. So you could say it is the “normal” form.

You might want to review the definitions of atomic number, atomic mass and isotope. The following link has a good explanation of these terms and how they are related. And I’m sure that a bit of online searching will reveal many more references to these topics.

https://www.khanacademy.org/science/bio ... es-article

I hope this helps. Please post again if you have more questions.

A. Norman