Elements with the same number of protons but different numbers of neutrons are known as what?

Elements with the same number of protons but different numbers of neutrons are classified as isotopes. The number of protons in an atom defines the element and determines its atomic number. However, variations in the number of neutrons lead to different isotopes of that element. For example, carbon has several isotopes, including carbon-12 and carbon-14, which differ in their neutron count but share the same atomic number and properties related to their electronic structure.

Molecules refer to groups of two or more atoms bonded together, which does not specifically relate to protons and neutrons. Ions are atoms or molecules that have gained or lost electrons, resulting in a charge, but this concept does not pertain to variations in neutron numbers. Allotropes denote different structural forms of the same element in the same physical state, such as carbon's diamond and graphite forms, and do not involve differing neutron counts.