What is the difference between an element's atomic number and its atomic weight?

The atomic number of an element is defined as the number of protons found in the nucleus of an atom. It uniquely identifies an element and determines its position in the periodic table. For example, hydrogen has an atomic number of 1, indicating it has one proton. The atomic number also influences the element's chemical properties and behavior.

Atomic weight, often referred to as atomic mass, is the weighted average mass of an element's isotopes, measured in atomic mass units (amu). It takes into account the relative abundance of each isotope in nature. For instance, carbon has an atomic weight of approximately 12.01 amu, reflecting the presence of both carbon-12 and carbon-13 isotopes. Unlike atomic number, atomic weight is not a whole number due to the presence of isotopes.

Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons, resulting in different atomic masses. For example, carbon-12 and carbon-14 are isotopes of carbon, with 6 protons but differing neutron counts. The existence of isotopes is crucial for understanding atomic weight, as the average is calculated based on the relative abundances of these isotopes in nature.