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500 BCE
The Alchemists
They developed the theory that all metals are composed of mercury and that you change metals into gold. They broke down the 4 elements Fire, Earth, Wind, and Water. -
450 BCE
Aristotle
Aristotle did not believe in the atomic theory. He thought that that the materials on earth were made up out of the 4 elements. -
428 BCE
Plato
Plato believed that there exists an immaterial Universe of forms.The objects and ideas in our material world are shadows of the forms. -
400 BCE
Democritus
Democritus introduced the idea of the atom as the basic building block matter. He thought that all atoms are small, and that the atoms are surrounded by empty space and moving all the time randomly. He suggested that all matter was formed of different types of discrete particles and that the properties were determined by properties of matter. -
330 BCE
The Solar System
The Bohr or solar system model of the atom states that atoms consist of a nucleus with a number of electrons in orbit around that nucleus. -
Robert Boyle
Robert discovered that the volume of gas decreases with increasing pressure or either or. It was known as Boyle's law. -
Lavioiser
He determined that oxygen was a key substance in combustion, and he gave the element his name. Through a series of experiments Lavoisier found that the total mass of products and reactants in a chemical reactions is always the same. This led to the theory of the law of conservation of mass. -
Solid Sphere of "Billiard Ball" Model
The Solid Sphere was founded by John Dalton.Since he thought the atoms were so small, he envisioned them as solid spheres. He used wooden balls to model them. -
John Dalton
He proposed that all matter is made of tiny invisible particles, he imagined them as solid, messy, and hard moveable particles. -
Dimitri Mendeleev
Mendeleev found that when all the known chemical elements were arranged in order of increasing atomic weight. -
J.J Thompson
His experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. -
The Curies
Marie and Pierre Curie successfully isolate radioactive radium salts from the mineral pitchblende in a laboratory in Paris. They discovered the existence of the elements radium and polonium in their research of pitchblende. -
Plum Pudding Model
Thomson's Model showed an atom that had a positive charge medium and it has negatively charged electrons. His experiment with cathode ray tubes showed that all atoms contain tiny negative charged subatomic particles or electrons. -
Albert Einstein
Einstein mathematically proved the existence of atoms. Einstein explained the photoelectric effect. He showed that when quanta of light energy strikes atoms in the meta. The quanta force the atoms to release electrons. Einstein's work helped justify the quantum theory. -
Robert Milikan
He succeeded in precisely determining the magnitude of the electron's charge. -
Ernest Rutherford
He postulated the nuclear structure of the atom. He discovered alpha and beta rays and proposed the laws of radioactive decay. He believed that the mass and positive charge were concentrated in a small region called the nucleus. -
Neils Bohr
Neils Bohr made a theory for the hydrogen atom based on quantum theory that energy is transferred only in well defined areas. He discovered that electrons should move around the nucleus, but only in prescribed orbits. When jumping from one orbit to another with lower energy, a light quantum is emitted. -
Henry J. Mosely
He observed and measured the X-ray spectra of various chemical elements from crystals. He discovered a systematic relation wave length and atomic number. It is Mosely's law. -
Electron Cloud Model
The electron Cloud Model was developed by Erwin Schrodinger and Werner Heisenberg. It was consisted of a dense nucleus surrounded by cloud of electrons at certain levels.They determined regions mathematically in which electrons would most likely be found. -
Werner Heisenberg
He was a German physicist and philosopher who discovered a way to formulate quantum mechanics in the terms of matrices. He discovered the uncertainty principle, which states that a particle's position and momentum cannot both be known exactly.
