The atomic number and atomic mass are two different properties associated with atoms:
Atomic Number: The atomic number of an atom represents 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, helium has an atomic number of 2, and so on. In a neutral atom, the atomic number also corresponds to the number of electrons surrounding the nucleus.
Atomic Mass: The atomic mass of an atom represents the mass of the atom, taking into account the protons, neutrons, and electrons. It is often expressed in atomic mass units (amu) or unified atomic mass units (u). The atomic mass is determined by the total number of protons and neutrons in the nucleus, as electrons contribute negligibly to the overall mass. The atomic mass is not necessarily a whole number because it considers the average mass of all the naturally occurring isotopes of an element, weighted by their abundance. It can be found in the periodic table for each element.
In summary, the atomic number is the count of protons (and electrons) in an atom, uniquely identifying the element, while the atomic mass is the mass of the atom, accounting for the combined mass of protons and neutrons in the nucleus.