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300
Democritus
He said that matter was made up of invisible particles called atoms. He believed that everything is made of tiny things that never get deleted, they can only be moved or changed. -
Period: 300 to
Atomic Theory
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Antoine Lavoisier
He is most noted for his discovery of the role oxygen plays in combustion. He also wrote the first extensive list of elements, helped to reform chemical nomenclature, and he stated the first version of the law of conservation of mass. -
Law of Conservation of Mass
A fundamental principle of classical physics that matter cannot be created or destroyed, but conserved. -
John Dalton
Responsible for the basis of atomic theory "Billiard Ball Model" which represents an atom as a solid ball of matter with no moving parts. His model only shows that atoms of the same element have the same masses, atoms of different elements have different masses, and that atoms of different elements combine in definite proportions to form compounds. -
Dalton's Atomic Theory
1) All matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties.
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of atoms. -
Dmitri Mendeleev
He discovered that the properties of elements tended to repeat after a certain period of increasing proton number. It led directly to the Periodic Table and enabled the discovery of new elements where there were gaps in the table. He could predict properties of undiscovered elements. -
Cathode Ray Tube
An electric current passed through a gas inside a sealed tube. -
JJ Thompson
Discovered the electron, determined the mass to charge a ratio of the particles, proposed 'plum pudding model' -
Plum Pudding Atomic Model
Founded by JJ Thomson, he said that the atomic structure consisted of just a bunch of electrons floating around in a positively charged goo of sorts that balanced the negative charge of the electrons. It was later shown to be false when Rutherford and his colleagues performed the famous gold foil experiment and "discovered" the nucleus was a concentrated mass of positive charge rather than a spread out soup. -
Robert Millikan
Discovered that the accurate determination of the charge carried by an electron, using the elegant "falling-drop method"; he also proved that this quantity was a constant for all electrons thus demonstrating the atomic structure of electricity. -
Rutherford Model
first modern concept of atomic structure; all of the positive charge and most of the mass of the atom are contained in a compact nucleus; a number of electrons (equal to the atomic number) occupy the rest of the volume of the atom and neutralize the positive charge. -
Henry Moseley
He developed the application of X-ray spectra to study atomic structure; his discoveries resulted in a more accurate positioning of elements in the Periodic Table by closer determination of atomic numbers. -
Bohr Planetary
used as a symbol for atomic energy. In the Bohr Model the neutrons and protons occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun. -
Niels Bohr
the electrons absorb and emit radiation of fixed wavelengths when jumping between the fixed orbits around a nucleus. The theory gave a good description of the spectrum from the hydrogen atom, but must be further developed for more complicated atoms and molecules. Assuming that matter, e.g. electrons, could be regarded both as particles and as waves. -
Erwin Schrodinger
Famed for his contributions to quantum mechanics, especially the Schrodinger equation. -
Quantum Mechanical Model
The quantum mechanical model is based on quantum theory, which says matter also has properties associated with waves. According to quantum theory, it’s impossible to know the exact position and momentum of an electron at the same time. This is known as the Uncertainty Principle. The quantum mechanical model of the atom uses complex shapes of orbitals (sometimes called electron clouds), volumes of space in which there is likely to be an electron. -
Gold Foil Experiment
having a central positive nucleus surrounded by negative orbiting electrons. This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space. Rutherford came to this conclusion following the results of his famous gold foil experiment. This experiment involved the firing of radioactive particles through minutely thin metal foils (notably gold) and detecting them using screens coated with zinc sulfide (a scintillator). -
Ernest Rutherford
best known for establishing the theory of the nuclear atom, and is known as the father of nuclear physics. -
James Chadwick
discovered the neutron in the atomic nucleus. He received the Nobel Prize for the discovery -
Electronic Cloud Model
mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom.[1] This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus
