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400 BCE
Democritus: The Father of Modern Atomic Thought
Democritus was a greek philosopher who lived from 470-380 BC. He proposed that matter couldn't be divided into smaller pieces forever. He did so by smashing seashells into fine pieces and eventually into dust and theorized that you could not break down the fine particles anymore or forever. He called these smallest particles atoms which means “indivisible” in Greek. -
John Dalton: The Creator of the Atomic Theory
John Dalton was an English school teacher who lived from 1766-1844. He performed many science experiments on atoms. He believed that atoms are tiny, invisible particles, atoms of one element are all the same, atoms of different elements are all different and that compounds form by combining atoms. Dalton concluded that if there are two elements that can combine, their combinations will occur in a set sequence. -
JJ Thomson: The Founder of the Electron
JJ Thomson was an English physicist who lived from 1856 to 1940. Thomson helped the atom evolve over time by discovering the electron in 1904. He did so by using a cathode ray tube.Thomson set out to see if the charge carried by the cathode rays was negative or positive, he would use an electric field to do this. He put a negatively charged metal plate on one side of the cathode rays let out past the anode, and a positively charged metal plate on the other side. -
Rutherford: The Founder of Protons and the Nucleus
Ernest Rutherford was a physicist who was from New Zealand. He lived from 1871 to 1937. Rutherford discovered the nucleus and protons by placing radium (Ra) in a lead box with a small opening on one side. He then shot alpha particles of radium out of the box at a small piece of gold foil. He put a detector screen around the gold sheet to determine where the alpha rays end up after contacting the gold foil. -
Neils Bohr Atomic Model
Neils Bohr was a Danish physicist who studied under Ernest Rutherford. He proposed that electrons can only be found in specific circular paths (orbits) around the nucleus and that electrons travel on paths with fixed energies, called energy levels. He also concluded that electrons can gain or lose energy by changing its orbit. This is called a "quantum jump". -
Erwin Schrödinger: The Founder of the Quantum Mechanical of the Atom
Erwin Schrödinger was an Austrian born physicist who discovered the Quantum Mechanical model of the atom. Schrödinger concluded that electron clouds describe probability of where an electron might be found and electrons can only have certain energy levels. He also stated that electrons occupy only certain orbits around the nucleus. Those orbits are stable and are called "stationary" orbits.
