Pioneers of Atomic Theory
John Dalton kicked off our modern understanding of atoms in 1808. His Atomic Theory proposed that elements are made of tiny particles called atoms, and that atoms of the same element are identical. He also explained that compounds form when different elements combine in simple ratios, and that atoms just rearrange during chemical reactions—they don't disappear or get created.
Dimitri Mendeleev revolutionized chemistry in 1869 by creating the Periodic Table. What made his work amazing was that he left blank spaces for elements that hadn't been discovered yet! He could even predict what these unknown elements would be like based on where they belonged in his table.
J.J. Thompson made a huge breakthrough in 1897 when he discovered the electron through his Cathode Ray Tube experiments. He found that no matter what element he used, the same tiny, negatively charged particles came out. This led to his "Plum Pudding Model" of the atom—a positive mass with electrons scattered throughout, like raisins in pudding.
Fun Fact: Scientists once thought atoms were indivisible (couldn't be broken down). Thompson's discovery of electrons proved this wrong and showed that atoms have smaller parts inside them!