What you learned in school
Chemistry textbooks taught that atoms were indivisible particles - the smallest possible units of matter. Students learned that the word "atom" meant "uncuttable" in Greek. Dalton's atomic theory presented atoms as solid, indestructible spheres that couldn't be broken down further, making them the fundamental building blocks of all matter.
What we know now
Chemistry and physics textbooks taught that atoms were indivisible - the smallest possible particles of matter. The word "atom" comes from Greek meaning "uncuttable." Students learned that atoms were like tiny solid spheres that couldn't be broken down further. The discovery of electrons, protons, and neutrons revealed that atoms have internal structure. Further research found even smaller particles: quarks, leptons, bosons, and hundreds of other subatomic particles. Atoms are actually mostly empty space with a tiny nucleus surrounded by electron clouds.