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Democritus proposes that the model of an atom is made up of tiny, invisible, indestructible, particles called “atoms” moving through an empty space. -
the Greek philosopher Socrates was sentenced to death in Athens for impiety and corrupting the youth -
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John Dalton proposes atoms of each element are identical in mass and properties atoms of different elements vary in these characteristics. He explained that compounds form when atoms of different elements combine in simple whole-number ratios, and that chemical reactions involve only the rearrangement of these atoms, which are never created or destroyed. -
a journey led by Captain Meriwether Lewis and William Clark to explore the newly acquired Louisiana Purchase from St. Louis to the Pacific Ocean -
Faraday demonstrated that a continuous circular motion could be produced using the interaction between electricity and magnetism, showing that an electric current could create a magnetic field and that this magnetic field could in turn produce mechanical motion. -
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Eugen discovered canal rays streams of positively charged particles that formed in gas discharge tubes and traveled in the opposite direction of cathode rays. He observed these rays passing through small holes, or “canals,” in the cathode, which allowed them to be detected behind it. -
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JJ Thompson discovered the electron while studying cathode rays in vacuum tubes. By measuring how these rays deflected in electric and magnetic fields, he concluded that they were made of tiny, negatively charged particles much smaller than atoms, challenging the long-held belief that atoms were indivisible. -
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The Wright brothers make the first successful airplane flight -
Robert Millikan conducted the oil drop experiment, through which he precisely measured the electric charge of the electron. By observing tiny charged oil droplets suspended between electrically charged plates, Millikan determined the exact value of the electron’s charge and showed that electric charge is quantized, occurring in discrete units. -
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Ernest Rutherford discovered the atomic nucleus through his famous gold foil experiment. By directing alpha particles at a thin sheet of gold foil, he observed that while most particles passed straight through, a small number were deflected at large angles. This unexpected result showed that atoms are mostly empty space but contain a tiny, dense, positively charged center, the nucleus. -
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Niels Bohr introduced a new model of the atom by proposing that electrons orbit the nucleus in fixed energy levels and can move between these levels by absorbing or emitting specific amounts of energy. This idea explained the observed spectral lines of hydrogen and resolved problems in Rutherford’s nuclear model by incorporating early quantum theory -
A cease-fire was signed in a railroad car in Compiègne, France, effectively ending the fighting on the Western Front. -
Werner Heisenberg developed matrix mechanics, the first complete and consistent formulation of quantum mechanics. Instead of describing electrons by visual orbits, he used mathematical matrices to represent observable quantities like energy and frequency. -
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Erwin Schrödinger developed the wave equation that describes electrons as wave-like entities rather than particles moving in fixed orbits. This breakthrough formed the foundation of quantum mechanics and led to the quantum mechanical model of the atom, in which electrons occupy regions of space called orbitals defined by probability rather than precise paths. -
The stock market crash, widespread bank failures, and a sharp drop in consumer demand -
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James Chadwick discovered the neutron, a neutral particle found in the nucleus of atoms. He demonstrated its existence by bombarding beryllium with alpha particles, which produced a highly penetrating radiation that was not deflected by electric fields. -
The United States enters World War II after Japan attacks Pearl Harbor in December.