An isotope differs from the standard form of a chemical element primarily in the number of neutrons in its nucleus. While all atoms of a given element have the same number of protons (which defines the element), isotopes have different numbers of neutrons, resulting in different atomic mass numbers but the same atomic number

. Key points of difference include:

• Protons: The number of protons is the same in isotopes and the standard form of the element, ensuring they are the same chemical element.
• Neutrons: Isotopes have a different number of neutrons compared to the standard form, which changes their mass but not their chemical identity.
• Atomic Mass: Because of the neutron difference, isotopes have different atomic masses.
• Chemical Properties: Isotopes generally have very similar chemical properties since chemical behavior is determined by electron structure, which is the same across isotopes of an element.
• Physical Properties: Isotopes can have different physical properties due to their mass differences

For example, carbon has isotopes carbon-12, carbon-13, and carbon-14, all with 6 protons but with 6, 7, and 8 neutrons respectively, leading to different mass numbers but the same chemical element identity

. In summary, an isotope is a variant of a chemical element that shares the same number of protons but differs in neutron count, distinguishing it from the element's standard form by atomic mass and some physical properties.