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415 BCE
Democritus
A Greek philosopher who developed the concept of an 'atom' AKA 'invisible' in Greek for how extremely tiny it is. For his discovery, he took a seashell and broke it in half and he continued to break it in half over and over again until he was left with a powder. He took the smallest piece of the powder and tried to break it and couldn't. He they discovered atoms are like that powder, unbreakable and they're the main building blocks. -
Dalton
Developed first useful atomic theory of matter. He concluded that evaporated water exists in the air as an independent gas. He reasoned that if the water and the air were composed of discrete particles, evaporation might be viewed as a mixing of water particles with air particles. He performed a many experiments on mixtures of gases to determine what effect properties of the individual gases had on the properties of the mixtures as a whole. -
Thompson
Discovered the electron when he was experimenting with gas discharge tubes. Noticed a movement in the tube and called it "cathode rays". Rays moved from negative to positive because opposites attract. He later named the rays "electrons". -
Rutherford
Conducted a famous experiment called the Gold Foil Experiment because he used a gold sheet of foil. Used special equipment to shoot positively charged particles he called alpha particles at the gold foil. He made the claim that an atom was mostly empty space because most particles passed through the foil. He figured out that the nucleus was positively charged because the alpha particles repelled the nucleus and like charges repel. He was also responsible for the nuclear model of the atom. -
Bohr
He proposed that the electrons go around the nucleus like planets orbit the sun. He also said that the electrons have energy levels and the higher the energy level, the more electrons it can hold. When the energy goes down, the level does too. This model is called the Bohr-Rutherford model because Bohr used many of Rutherford's ideas.
