What Are the 3 Particles That Make Up an Atom?
Every atom is made of three subatomic particles: protons, neutrons, and electrons. These are the 3 particles that make up an atom, and they determine every physical and chemical property of an element. Protons and neutrons cluster in the dense nucleus at the center, while electrons orbit around that nucleus in a cloud.
Protons, Neutrons, and Electrons
A proton carries a positive electric charge of +1 and has a relative mass of about 1 atomic mass unit (amu). The number of protons in an atom defines the element — for example, any atom with 6 protons is a carbon atom. The International Union of Pure and Applied Chemistry (IUPAC) maintains the official list of elements based on proton count.
A neutron has no electric charge (it is neutral) and a mass very close to that of a proton, about 1.008 amu. Neutrons stabilize the nucleus; without them, protons of the same charge would repel each other and the nucleus would fly apart. Atoms of the same element can have different numbers of neutrons — these variants are called isotopes.
An electron has a negative charge of -1 but a mass roughly 1/1836 that of a proton — so small that chemists usually treat its mass as negligible. Electrons occupy orbitals around the nucleus, and their arrangement determines how an atom bonds with other atoms. The Royal Society of Chemistry provides detailed resources on electron configurations.
A quick concrete example: a carbon-12 atom has 6 protons, 6 neutrons, and 6 electrons. The 6 protons make it carbon; the 6 neutrons give it a mass number of 12; the 6 electrons balance the charge and allow it to form four chemical bonds.
Key Takeaways
- Protons are positively charged particles in the nucleus that define which element an atom is.
- Neutrons are neutral particles in the nucleus that add mass and help hold the nucleus together.
- Electrons are negatively charged particles that orbit the nucleus and control chemical bonding.
- The number of protons is fixed for a given element, but the number of neutrons can vary (isotopes), and electrons can be gained or lost in chemical reactions.
