Atom Calculator

An atom is the smallest unit of matter that retains the chemical properties of an element. It consists of a central nucleus containing protons and neutrons, surrounded by a cloud of electrons. Protons and neutrons are collectively called nucleons.

Atoms are made of three subatomic particles: positively-charged protons and electrically neutral neutrons (both in the nucleus), and negatively-charged electrons that orbit the nucleus. The number of protons determines which element the atom belongs to.

The atomic number (Z) equals the number of protons in the nucleus. For example, carbon has 6 protons, so its atomic number is 6. The atomic number uniquely identifies an element on the periodic table.

The mass number (A) is the total count of protons and neutrons in the nucleus: A = protons + neutrons. For a carbon-12 atom with 6 protons and 6 neutrons, the mass number is 12. Electrons are not included because their mass is negligible.

Helium always has 2 protons (Z = 2). With 2 neutrons, the mass number A = 2 + 2 = 4. This is the most common isotope, helium-4.

Protons give an atom its identity. The number of protons — the atomic number — determines which element an atom is. Changing the proton count transforms it into a different element entirely.

The atomic number equals the number of protons, so Z = 6. This is carbon. With 7 neutrons, the mass number is 13, making it carbon-13, a stable isotope of carbon. Because electrons equal protons, the atom is electrically neutral.

Atomic charge = protons − electrons. A neutral atom has equal protons and electrons (charge = 0). If an atom loses electrons, it becomes a positively charged cation. If it gains electrons, it becomes a negatively charged anion.