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400
Aristotle
The Atom had been introduced by Democritus. Aristotle did not believe in the Atom Theory. Aristotle believed that all matter was made of "The Four Elements" which are fire, earth, air, and water. He did not have any proof to support his theory. The Atom Theory had no proof as well. -
400
Aristotle's Followers
People believed and supported Aristotle's theory because in that time Aristotle was one of the greatest minds and had many followers. -
460
Democritus
Atomic Theory revolved around atoms that are present in the atmosphere. Theory explains the esistance in atoms and its features. Attempted to create Materialism. -
460
Atoms
He began with the idea that everything cold be broken down into smaller pieces. This is how he came upon his Atom Theory. To Democritus the atom looked like a marble. -
Dalton's Laws
Dalton published his law of partial pressures known as Dalton's Law. Dalton's Law says that when different gases combine, the resulting pressure will be the sum of what each gas gives individually. -
Dalton
Dalton's studies led to the conclusion that gases had to be made of small particles. Taking and increasing Democritus' idea that atoms could not be split, Dalton created the new atomic theory. He said that all matter is made of small and invisible parts, they are not capable of being destroyed and that they could not be changed. -
Sir William Crookes
Sir William invented a tube where he could see some sort of particle beam going from the negative cathode to the positive anode. -
Sir William Discovers Thallium
Sir William discovered the element Thallium. He also invented the Crookes tube, which he used in many experiments while dealing with Thallium, led to other inventions by other scientists such as the x-ray. -
Millikan and Thomson
Robert finished the atomic model with Thomson. Millikan was like Broglie, loved to deal with electrons. Robert's Oil Drop Experiment was the downward gravitational force with the upward buoyant and electric forces. -
Rutherford's Experiments
The Gold-Foil Experiment was where he shot alpha particles at gold foil, expecting them to pass right through. Some bounced back, however, and he formulated the planetary model, which showed that most of the mass of an atom was concentrated in the center (nucleus). -
Crookes' Experiments
Sir William Crookes' experiments with cathode-ray tubed led him to confirm that cathode-rays have a negative charge -
J.J. Thomson
J.J. Thomson discovered the electron. -
"Plum Pudding"
Discovering the electron led J.J. to create the "plum pudding" atomic model. In this model, he thoiught that the atom was mostly positive, and negative electrons wandered around the atom. The "plum pudding" model influenced other scientists to make better atomic models. -
Thomson's Suggestion
Thomson suggested a model of the atom as a sphere of positive matter in which electrons are positioned be electrostatic forces. -
Robert Millikan
Robert's measurement of the charge of an electron and his work on the photoelectric effect are very famous. He came up with using an oil drop experiment where he measured the charge of an electron. -
Oil Drop - Millikan
Through the Oil Drop experiment, Millikan and his partner deemed the approximate value of the electron as 1.5924(17)x10^-19C, which is within 1% of the present day accepted value. -
Ernest Rutherford
Rutherford analyzed that J.J. Thomson's model was incorrect. He came up with the region which he called the nucleus. Rutherford created his gold-foil experiment. -
Rutherford Atomic Model
Rutherford thought that electrons in the atom just float freely but that wasn't the case. -
Bohr
Niels Bohr contribution to the atom model helped greatly improve our understanding of the atom in general. He was only able to do so thanks to Rutherford's early model of the atom saying that it had a positively charged nucleus with a negatively charged electron orbiting the nucleus. -
Niels Bohr
Bohr proposed that electrons orbited in larger orbits and that the farther away the electron is from the nucleus the more electrons that layer can hold. And it is this that determines the chemical property. -
Bohr Part II
He later on suggested that atoms emitted radiation when they jump from outer orbit clouds to the inner ones. -
Henry Moseley
Moseley measured the wavelengths of the x-rays given off by certain metals, he was able to determine the number of positive charges in the nucleus of an atom. This was the first concept of the atomic number. -
The Curies
A rare and highly radioactive metalloid, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. -
Curies
Polonium has been studied for possible use in heating spacecraft. This is important to the world around us because it impacts the world of science. -
Aristotle's Belief
Aristotle felt that regardless of the number of times you cut a form of matter in half, you would always have a smaller piece of that matter.
