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350
Aristotle
In 350 BC, Aristotle made a model based on the four elements. Today we know that there are more than four elements, but what he did get right was that there are four states of matter - solid, liquid, gas, and plasma. He believed everything was made of certain amounts of fire, air, water, and earth. -
Period: 450 to
450 BC - 1932
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465
Democritus
In 465 BC, a Greek philosopher named Democritus had one of the earliest perceptions about atoms. He knew that; all matter consists of atoms, atoms are indescructible, atoms are solid but invisible, atoms are homogenous, atoms differ in shape, mass, position and arrangement, His theory wasn't entirely correct, but it did allow other scientists to use his theory as the building blocks for their theories. -
John Dalton
In 1803, John Dalton came up with an atomic theory. His theory was that elements consist of tiny particles called atoms. According to his theory, elements are pure because all atoms of an element are identical and they have the same mass. Dalton came to his theories based on what he researched about gases. He saw that only certain gases could be combined in certain proportions, even if the compounds were different and had the same element. He did some deductive reasoning and made this discovery -
Marie Curie
In 1898, Marie Curie and her husband Pierre studied uranium and thorium and defined radioactivity. They also discovered the radioactive elements polonium and radium. Marie Curie’s daughter had a shortcoming when studying radioactive elements – and James Chadwick used that fault as the building blocks for his theory. -
Albert Einstein
In 1905, Albert Einstein formulated the Special Theory of Relativity. He set laws of mass-energy equivalence, which led to his E=mc2. This theory is based on the fact that only relative motion can be measured. These almost entirely contradicted Isaac Newton’s laws of motion, including intertia. -
Ernest Rutherford
Discovered in 1911, the Rutherford atomic model, proposed by Ernest Rutherford, described an atom as a small, dense, positively charged core (nucleus), and inside all of the mass is concentrated. Around this, the light and electrons revolve like planets around the sun. He gave “alpha” and “beta” names to certain types of radiation. His model did not include neutrons to start out with, but they were discovered after his model was created. -
Niels Bohr
In 1913, Niels Bohr stated he had a theory for the hydrogen atom based on quantum theory that energy can be transferred only in certain defined amounts. Electrons move around in the nucleus, but only in specific orbits. His theory could be used to explain why atoms give off light in wavelengths. His model sort of built on Ernest Rutherford’s model, as it was proposed after the discovery of the electron and radioactivity. -
James Chadwick
In 1932, James Chadwick discovered the neutron. He did nuclear research during his school years, and looked more into the nucleus. He learned about how some other scientists had released protons from wax using gamma rays. He was confused, and withdrew the conclusion that the protons had been hit by the neutron. He used polonium as the source of neutrons, and used wax also. Protons were released and he made measurements of their behavior.
