Distinguish between atomic number and atomic mass number.

Atomic number is the number of protons in the nucleus. The atomic mass number (I prefer to leave the word atomic off and just call it mass number) is the number of protons and neutrons (protons and neutrons may be called nucleons) in the nucleus.

The atomic number and atomic mass number are both important properties that describe atoms.

The atomic number of an atom is a unique identifier for that element, representing the number of protons in the nucleus of an atom. Each element on the periodic table has a distinct atomic number that differentiates it from other elements. The atomic number is denoted by the symbol Z and is typically located at the top-left corner of an element's symbol.

To find the atomic number of an element, you can refer to the periodic table. The periodic table is arranged in increasing order of atomic numbers. For example, the atomic number of hydrogen is 1, meaning it has one proton, while the atomic number of helium is 2, indicating it has two protons.

On the other hand, the atomic mass number of an atom represents the total number of protons and neutrons in an atom's nucleus. It is denoted by the symbol A. Since protons and neutrons have similar masses, the atomic mass number is approximately equal to the total number of nucleons (protons + neutrons) in an atom.

To find the atomic mass number of an element, you can also refer to the periodic table. It is usually expressed below the symbol of the element. Since the number of neutrons can vary within different isotopes of an element, the atomic mass number is often given as an average value, taking into account the different isotopes and their relative abundance.

In summary, the atomic number represents the number of protons in an atom, while the atomic mass number represents the total number of protons and neutrons.