In chemistry, what is the atomic number?

Get ready for your General Education Test with our structured study tools, featuring flashcards and multiple-choice questions. Access detailed explanations for each question to boost your confidence and ensure a successful exam experience!

The atomic number is the number of protons in the nucleus. This count uniquely identifies an element and places it on the periodic table, since each element has a specific proton count. In a neutral atom, the number of electrons matches the atomic number, but the electron count can differ in ions, so electron number isn’t the defining property. The mass number, on the other hand, is the sum of protons and neutrons, not just protons, and the number of neutrons can vary among isotopes. So the essential idea is that the atomic number counts protons, which fixes the element’s identity.