Define atomic mass and atomic number?
These two terms are connected. So, an atom is composed of a nucleus and one or more electrons. The nucleus is composed of protons and neutrons. Protons, neutrons and electrons combined together make the Atomic Mass of an atom, the more subatomic particles you have the more mass you have. Now, every atom has a different number of protons and because of that, that’s how they are arranged in the periodic table. So the atomic number is the number of protons in an atom.
I hope this helps.
The most commonly used scale is atomic number. Atomic mass can differ a lot but the periodic table and elsewhere in research, atomic number is used.
For students, I would recommend to memorize understanding.