An element's atomic number, atomic mass, and proton number are related but represent different aspects of an element:
Atomic Number: The atomic number of an element corresponds to the number of protons in the nucleus of an atom. It uniquely identifies the element and determines its position in the periodic table. Each element has a distinct atomic number, and elements are arranged in ascending order of atomic numbers in the periodic table.
Proton Number: The proton number is another term for the atomic number. It refers to the count of protons present in the nucleus of an atom. Protons are positively charged particles, and their number determines the chemical properties and identity of an element.
Atomic Mass: The atomic mass of an element represents the average mass of all the isotopes of that element found in nature. Isotopes are atoms of the same element that have different numbers of neutrons but the same number of protons. Atomic mass takes into account the relative abundance of each isotope and their respective masses. It is usually expressed in atomic mass units (amu).
In summary, the atomic number and proton number are interchangeable terms representing the number of protons in an element's nucleus. Atomic mass, on the other hand, is the average mass of all the isotopes of an element, taking into account their relative abundances. While the atomic number and proton number are whole numbers, the atomic mass is usually a decimal value due to the presence of different isotopes.