If you could peek inside an atom, you would see a lot going on. First you might notice its small, tightly-packed center. This is called the nucleus (NOO-klee-uhs). Inside the nucleus are even tinier particles. They are called protons (PROH-tons) and neutrons (NOO-trons). There are around the same number of protons and neutrons in an atom. Squeezed tightly together, they form the nucleus.
Look again, and you will see clouds of particles called electrons (uh-LEK-trons). They orbit around the nucleus. The same number of electrons and protons are in each atom.
Protons and electrons each have a charge. In protons, the charge is positive. In electrons, the charge is negative. Together, they balance the atom’s charge. The atom as a whole is neither positive nor negative.
For a long time, scientists thought they knew all the parts of an atom. Then they learned that there is more. Protons and neutrons are made of something even smaller. They are tiny particles called quarks (kwarks). Quarks are the smallest parts of an atom.
