Isotopes of the same element differ in the number of neutrons in their nuclei. This means they have the same number of protons and electrons, hence the same atomic number, but different mass numbers due to the varying number of neutrons. This difference in neutrons causes isotopes to have different atomic masses and some different physical properties such as density, melting point, and boiling point. However, they share almost identical chemical properties because chemical behavior is primarily determined by the number of protons and electrons, which are the same in isotopes of an element. Additionally, some isotopes are stable while others are radioactive and unstable.

Key Differences of Isotopes

• Same number of protons (same element identity).
• Different number of neutrons.
• Different atomic mass.
• Similar chemical properties.
• Different physical properties (e.g., density, boiling/melting points).
• Some isotopes are stable; others are radioactive.

For example, carbon has isotopes like carbon-12 (6 neutrons), carbon-13 (7 neutrons), and carbon-14 (8 neutrons). All have 6 protons, so they remain carbon atoms but differ in mass and stability.

Thus, isotopes of the same element primarily differ by neutron count, leading to variations in mass and certain physical and nuclear properties, while maintaining consistent chemical behavior.