Two atoms of the same element have different numbers of neutrons in their nuclei. What are these two atoms called?

1. Atomic number, which fixes the element, depends only on the number of protons, not neutrons. 2. Atoms of the same element with different neutron counts are called isotopes of that element. 3. They remain the same element, so they are not different elements entirely. 4. Isomers and allotropes are chemistry terms for compounds and molecular forms, not for nuclear neutron variation. 5. So isotopes of the same element is correct. _Source: OpenStax Physics (CC BY 4.0), Ch 22 "The Atom", section 22.2 Nuclear Forces and Radioactivity_