The Physics Question Bank

Isotopes are different versions of the same element.

Atoms of the same element always have the same number of protons. This is what makes them that element.

For example, every carbon atom has 6 protons. If it did not have 6 protons, it would not be carbon.

Isotopes have the same number of protons, but different numbers of neutrons.

This means isotopes are still the same element, but they have different mass numbers.

The mass number is the total number of protons and neutrons in the nucleus.

For example:

Carbon-12 has 6 protons and 6 neutrons.

Carbon-14 has 6 protons and 8 neutrons.

They are both carbon because they both have 6 protons. However, they are different isotopes because they have different numbers of neutrons.

Some isotopes are stable. This means their nuclei do not break down.

Some isotopes are unstable. These are radioactive isotopes. Their nuclei can decay and give out radiation.

The key idea is this:

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.

AQA GCSE 3 mark answer

Isotopes are atoms of the same element. They have the same number of protons but different numbers of neutrons. This means they have the same atomic number but different mass numbers.