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460 B.C., did a Greek philosopher, Democritus, develop the idea of atoms
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Proposed a mechanical universe with small solid masses in motion.
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John Dalton is usually credited with developing the first coherent atomic theory.
Dalton's theory can be summarized as follows:
-Matter is composed of small particles called atoms.
All atoms of an element are identical, but are different from those of any other element.
-During chemical reactions, atoms are neither created nor destroyed, but are simply rearranged.
-Atoms always combine in whole number multiples of each other. -
Built one of the first gas discharge tubes ("cathode ray tube").
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Proposed electric and magnetic fields filled the void.
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Used a CRT to study "canal rays" which had electrical and magnetic properties opposite of an electron.
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the electron and proposed a model for the structure of the atom. Thomson knew that electrons had a negative charge and thought that matter must have a positive charge.
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In 1900 Max Planck, a professor of theoretical physics in Berlin showed that when you vibrate atoms strong enough, such as when you heat an object until it glows, you can measure the energy only in discrete units. He called these energy packets, quanta.
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Discovered that inert gases had a stable electron configuration which lead to their chemical inactivity.
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Ernest Rutherford
He discovered the existence of the atomic nucleus. He discovered this by using the Gold Foil Experiment or the Rutherford Experiment. -
In 1912 a Danish physicist, Niels Bohr
RULE 1: Electrons can orbit only at certain allowed distances from the nucleus.
RULE 2: Atoms radiate energy when an electron jumps from a higher-energy orbit to a lower-energy orbit. Also, an atom absorbs energy when an electron gets boosted from a low-energy orbit to a high-energy orbit. -
Not until 1919 did Rutherford finally identify the particles of the nucleus as discrete positive charges of matter. Using alpha particles as bullets, Rutherford knocked hydrogen nuclei out of atoms of six elements: boron, fluorine, sodium, aluminum, phosphorus, an nitrogen. He named them protons, from the Greek for 'first', for they consisted of the first identified building blocks of the nuclei of all elements. He found the protons mass at 1,836 times as great as the mass of the electron.
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Discovered the existence of isotopes through the use of a mass spectrograph.
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In 1924 a Frenchman named Louis de Broglie thought about particles of matter. He thought that if light can exist as both particles and waves. he showed what matter waves would behave like if they existed at all
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In 1926, a German physicist, Max Born had an idea about 'psi'
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1932 did the English physicist James Chadwick finally discover the neutron. He found it to measure slightly heavier than the proton with a mass of 1840 electrons and with no charge (neutral). The proton-neutron together, received the name, "nucleon."
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Werner Heisenberg concluded that charged particles bounce photons of light back and forth between them.
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Conducted the first controlled chain reaction releasing energy from the atoms nucleus.
