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440 BCE
Plato
Plato believed that there were not 2 elements (atoms and the void) but 4: earth, air, fire, and water. Some believed that plato's real name was aristocles. -
400 BCE
Democritus
The Greek philosopher Democritus suggested that all matter was formed of different types of tiny discrete particles and that the properties of these particles also determine the properties of matter. He is viewed by many the "father of modern science." -
500
The Alchemists
The alchemists contributed to the atomic theory by breaking down the chemical composition of fire, earth, wind, and water. they believed that metals were formed of 2 principles mercury, and sulfur, and tried to invent potions that would make people live forever. -
Antone Lavoisier
Antone Lavoisier contributed to the development of the atomic theory by grouping elements as simple substances, metals, non-metals and earthly simple substances based on their physical and chemical properties. He is known as the father of chemistry. -
Robert Boyle
Robert Boyle contributed to the atomic theory by demonstrating that matter is made of many particles that he called corpuscles, but that are now know as atoms. He was a founding fellow of the royal society. -
Billiard Ball Model
Created in the early 1800s, proposed by John dalton, he thought atoms were small, hard spheres with no internal parts, as the concepts of atomic nucleus and electrons were unknown at the time. -
John Dalton
Once considered the father of chemistry. John Dalton proposed the atomic theory by doing lots of experiments that provided evidence for the existence of atoms. His theory suggested that matter was compromised of indivisible and indestructible atoms with distinct masses and properties. In 1810 Dalton refused his Royal Society membership invitation. -
Amedeo Aogadro
Amedeo contributed to the atomic theory when he made a law that states that equal volumes of gases at the same pressure and temperature contain an equal number of molecules. -
Dmitri Mendeleev
Dmitri was a big contribution to the atomic theory as he created the periodic table himself. He jotted down symbols for chemical elements, putting them in order according to the atomic weight. Dmitri's father became blind in the year of Dimitri's birth and died in 1847. -
JJ thomson
Thomson contributed to the atomic theory by announcing his discovery that atoms were made up of smaller components. Thomson developed what became known as the plum pudding model where the electrons were implanted in a sphere of positive charge. He also began studying in college when he was only 14. -
Pierre and Marie curie
Perre and Marie contributed to the atomic theory when they discovered the strongly radioactive elements polonium, and radium. These elements naturally occur in in uranium minerals. The couple also won a nobel prize for physics. -
Plum Pudding Model
in 1904 Thomson developed the Plum Pudding Model. In this model the electrons were embedded in a uniform sphere of positive charge. -
Albert Einstein
Albert helped to develop the atomic theory by mathematically proving the existence of atoms. This helped revolutionize all the sciences. Through the statistics and probability he mathematically predicted the size of both atoms and molecules. He wrote his first scientific paper when he was about 16 years old. -
Robert Millikan
Robert Millikan succeeded in precisely determining the magnitude of the electrons charge using the oil drip experiment. Millikan was also an enthusiast tennis player. -
Ernest Rutherford
Rutherford contributed to the development of the atomic theory by describing the atom as having a tiny. dense and positively charged core called the nucleus. In 1908 he won the nobel prize in chemistry. -
Neils Bohr
Neils Bohr contributed to the atomic theory by proposing the theory for the hydrogen atom based on the quantum theory that some physical quantities only take discrete values. Bohr developed a new model of an atom called the solar system model. He also worked on the Manhattan Project during world war 2, which eventually led to the development of the atomic bomb. -
Henry G.J. Moseley
Henry contributed to the atomic theory when he reported that the frequencies are proportional to the square of whole numbers that are equal to the atomic number plus a constant. Henry also predicted the existence of 4 elements: technetium, promethium, hafnium and rhenium -
Solar System Model
In 1913 Neils Bohr developed a new model of an atom. He proposed that electrons are arranged in concentric circular orbits around the neucleus. This model is patterned on the solar system and is known as the planetary model. -
Werner Heisenberg
Heisenberg contributed to the atomic theory through formulating quantum mechanies in terms of matrices and in discovering the uncertainty principle. With the help of Erwin Schrodinger, Heisenberg was able to create the eletron cloud model which showed the positions of an electron in an atom. Heisenberg was awarded nobel prize in 1932 for physics. -
Electron Cloud Model
Erwin Schrodinger and Werner Heisenberg developed the electron cloud model, which visualized the most likely electron positions in an atom. The electron cloud model describes the atom as containing a dense nucleus of protons and neutrons surrounded by regions of space (clouds) where electrons are most likely to be found. -
James Chadwich
James contributed to the atomic theory when he made a fundimental discovery by proving the existence of neutrons. He was elected a fellow at the royal society.