The basic unit of a chemical element

The number of protons in the nucleus of a element

Protons plus Neutrons

This is where the electrons rotate

Lithium, Sodium, Potassium, rubidium, cesium, and francium very reactive

magnesium, calcium, strontium, barium, radium

groups 3-12 iron, manganese, chromium, copper

fluorine, chlorine, bromine, iodine, astatine

neon, argon, krypton, xenon, radon