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400
The Alchemists
Scientists thought that everything had to be made up of all f the four elements earth, air, fire, and water. -
400
Plato
Plato came up with the word elements in 400 BC. He also favored the four elements theory how everything was made up of four elements. -
430
Democritus
His theory was that matter could not be divided into smaller and smaller pieces eventually the smallest possible piece would be obtained. He named the smallest piece of matter an atomos. -
Robert Boyle
He believed that chemical experiments could demonstrate the truth of the corpuscularian philosophy. -
Lavoisier
He created the Law of Conversation of mass it states that matter can be changed from one form into another, mixtures can be separated or made, and pure substances can be decomposed, but the total amount of mass remains constant. -
Dmitri Mendeleev
Mendeleev predicted the existence and properties of new chemical elements. When these elements were discovered, his place in the history of science was assured. -
John Dalton
He found out that all elements are composed of atoms. -
JJ Thomson
He provided the first hint that an atom is made of even smaller particles. -
The Curies
Discovered radium and polonium. They studied radio activity. -
Albert Einstein
The speed of light in a vacuum was independent of the motion of all observers. This was the theory of special relativity. -
Rutherford
He worked on an experiment where he fired a stream of tiny positively charged particles at a thin sheet of gold foil. Rutherford concluded that an atom had a small positively charged center that repelled his positively charged “bullets.” -
Henry Mosely
Henry Moseley published the results of his measurements of the wavelengths of the X-ray spectral lines of a number of elements which showed that the ordering of the wavelengths of the X-ray emissions of the elements coincided with the ordering of the elements by atomic number. -
Bohr
His theory was that electrons move in orbits around the nucleus,pretty much like planets circle the sun. These orbits are located at certain distances from the nucleus. -
Electron Cloud Model
