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300
Aristotle
Aristotle disagreed with Democritis' theory and believed there was no such thing as seperate particles. His ideas were not contradicted (and agreed with) by anyone until the 17th century. He greatly slowed down the evolution of the atomic theory by saying it didn't exist. -
400
Democritus
Democritus adopted the theory that stated, "the universe is composed of two elements: the atoms and the void in which they exist and move." He came up with the first model of the atom which was simple since there wasn't a lot of information at the time Democritus. According to him atoms were small quantities of matter and he hypothesized that atoms cannot be destroyed, differ in size, shape, shape and temperature, are always moving, are invisible, and that there are infinite number of atoms. -
Period: 400 to
Events in the History of the Atomic Theory
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Joseph Proust
Proust stated the Law of Definite Proportions. The law states that the ratio of elements in a compound is always consistant. He believed that matter could be put together in certain patterns to make bigger, different, unique matter. -
John Dalton
His atomic theory included the following.. All matter is made of atoms, atoms of an element are identical in mass and properties, compounds are formed by a combination of two or more different kinds of atoms, and a chemical reaction is a rearrangment of atoms. -
Antoine Hanri Becquerel
Antoine was one of the discoverers of radioactivity which led him to accept the notion that some radiation comes from within the substance itself rather than by and it was the first successful scientific attempt to detect and measure the effect of an individual subatomic particle. -
Earnest Rutherford
Shot alpha particles through extremely thin gold foil and they reflected unexpectedly in different directions, showing that there was a nucleus, lead to the nuclear model of an atom, and found out the charge of atoms and began the understanding of the interior of an atom. -
Erwin Schrodinger
Schrodinger used mathematic equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the Quantum Mechanical Model of the atom. This model predicts the odds of the location of the electron. -
Neils Bohr
The Bohr Model was created by Bohr and is a planetary model in which the negativitely-charged electrons orbot a small, positively-charged nucleus. There is a gravitational force between the positively-charged nucleusand the negatively charged electrons. Main points are that electrons orbit the nucleus in orbits that have a set size and energy, thergy is related to size and lowest energy is found in the smallest orbit. -
Louis de Broglie
Louis' ideas were a basis for developing the wave mechanics theory. This theory has greatly improved our knowledge of the physical nature on the atomic scale and the wave nature of electrons. -
Werner Heisenberg
Werner's contribution to the atomic theory was that he calculated the behavior of electrons, and subatomic particles that also make up an atom. Instead of focusing on mainly scientific terms, this idea brought mathematics more into understanding the patterns of an atom's electrons. -
James Chadwick
James Chadwick performed radiation experiments with the goal of looking for a neutral particle.. One with the mass the same as a proton, with zero charge. His experiments were successful. He was able to determine that the neutron did exist and that its mass was about 0.1 percent more than the mass of a proton. He recieved a Nobel Prize for his discovery in 1935.
