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405 BCE
Democritus
He determined that everything was composed of atoms and that atoms were indestructible. He then created the Democritus model. His experiment included finding a seashell and breaking it in half until it was a fine powder and then he took the smallest piece and tried to break that in half but he couldn't he discovered the indivisible building block of the atom. -
400 BCE
First-evidence Based Atomic Theory
Democritus -
Atomic Theory
John Dalton contributed his idea that while all atoms of an element were identical, different elements had atoms of differing size and mass. His atomic theory proved: Everything is composed of atoms, which are the indivisible building blocks of matter and cannot be destroyed. The atoms of different elements vary in size and mass. Compounds are produced through different whole-number combinations of atoms and many more things. He also was the first scientist to make a paper on color blindness. -
J.J. Thomson
He created the plum pudding model. He contributed that the atom was composed of electrons. In his experiment, he used a cathode ray tube to show that atoms contain tiny negatively charged subatomic particles. -
Cathode Ray tube experiment
The Cathode Ray tube Experiment was done by J.J Thomson. It took over the course of three experiments for him to find discover the existence of electrons. He did this using a cathode ray tube, which is a vacuum-sealed tube with a cathode and anode on one end that creates a beam of electrons traveling towards the other end of the tube. -
Discovery of Electron
J.J Thomson by his Cathode Ray tube experiment. -
Neils Bohr
he took a small positively charged nucleus surrounded by orbiting electrons and discovered that electrons travel in separate orbits around the nucleus. He then created the Bohr Model -
Gold Foil Experiment
The Gold foil Experiment was done by Ernest Rutherford it shot minute particles at a thin sheet of gold. It was found that a small percentage of the particles were deflected, while a majority passed through the sheet. This caused Rutherford to conclude that the mass of an atom was concentrated at its center. -
Oil drop experiment
Robert A. Millikan and Harvey Fletcher did this to measure the charge of electrons. They suspended tiny charged droplets of oil between two metal electrodes by balancing downward gravitational force with upward drag and electric forces. Using the known electric field and the values of gravity and mass, Millikan and Fletcher determined the charge on oil droplets in mechanical equilibrium. By repeating the experiment, they confirmed that the charges were all multiples of some fundamental value. -
Robert Millikan
He discovered the size of the charge on an electron, he also discovered the smallest unit charge on an electron. In his experiments, he examined the course of charged water droplets in an electric field which led him to find out that the charges were just multiples of a number. He created the electron model of the atom. -
Determined the size of the charge on an electron
Robert Millikan -
Ernest Rutherford
He created the nuclear model of the atom and discovered the alpha and beta waves and created the laws of radioactive decay. He came upon this information by the gold foil experiment, he determined that when some of the gold was hit with the alpha particles that the gold atoms were mostly empty space. -
Discovery of Nucleus
Ernest Rutherford, discovered the Nucleus in 1911 by Ernest Rutherford basing on the 1909 Geiger Marsden gold foil experiment. -
Quantum Mechanical Model
Erwin Schrodinger furthered the Bohr model making the Quantum Mechanical Model, introduced the electron cloud (Using mathematics to calculate the likelihood of finding an electron in a certain position). He worked heavily in quantum theory, Schrodinger’s Cat experiment, Won a Nobel Prize for the Schrodinger Equation, during the time of Nazism he fully opposed the extreme and radical movement and later in life fled to Italy due to backlash he faced. -
Discovery of Neutron
James Chadwick -
Neutron Discovery
James Chadwick was a British physicist that lived from October 20, 1891, to July 24, 1974. He discovered the neutron in atoms using a Neutron Chamber in his experiments. Later he was the head of the British team on the Manhattan Project during the second world war. In 1945 he was Knighted in Britain for his achievements in Physics and received a Nobel Peace Prize for his discovery of the Neutron.
