Atomic numbers and atomic mass numbers are whole numbers because they represent the fundamental properties of atoms, which are indivisible and discrete units.
Atomic Number: The atomic number (Z) of an element represents the number of protons in the nucleus of an atom. Protons carry a positive charge, and each element has a unique number of protons. The atomic number determines the identity of the element. Since protons cannot be divided into fractions or partial units, the atomic number is always a whole number.
Atomic Mass Number: The atomic mass number (A) of an atom represents the total number of protons and neutrons in the nucleus. Neutrons have a mass similar to that of protons and also contribute to the mass of the atom. Both protons and neutrons have approximately equal masses of around 1 atomic mass unit (amu). Since protons and neutrons are indivisible particles, the atomic mass number is always a whole number.
It's important to note that the atomic mass listed on the periodic table is not always a whole number. It is a weighted average of the masses of all naturally occurring isotopes of an element, considering their relative abundances. Isotopes are atoms of the same element with different numbers of neutrons, which can slightly affect the overall mass. However, the atomic mass number itself is always a whole number.
In summary, atomic numbers and atomic mass numbers are whole numbers because they represent the discrete and indivisible nature of protons and neutrons, which make up the nucleus of an atom.