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370 BCE
democritus
He believed that elements could be broken down into a basic level, which couldn't be broken down any further called atoms. -
322
Aristotle
Aristotle was the first person to suggest that the world was made up of elements, which he believed to be Earth, Wind, Fire and Water. His theory was that elements are infinite and can be continuously broken down. -
robert boyle
he wrote a book overturning aristotle's idea of the 4 elements and replaced it with his idea that elements cannot be separated into simpler components using chemical methods -
antoine lavoisier
Lavoisier created a definition of element - indivisible particles which we have found no means of separating. -
joseph proust
he discovered the law of constant composition. he found that chemical compounds will always combine in constant proportions. -
john dalton
Democritus first suggested the existence of the atom but it took almost two millennia before the atom was placed on a solid foothold as a fundamental chemical object by John Dalton. All matter is made of atoms. -
joseph gay lussac
he discovered a fundamental law of gases which is the law of combining volumes. he discovered that water is made of one part oxygen and two parts of hydrogen. -
amedeo avogadro
he discovered that equal gas volumes at the same temperature and pressure will have the same number of molecules -
max planck
combined laws with the quantum hypothesis that energy is emitted in discrete quanta. -
henri becquerel
he discovered radioactivity using naturally fluorescent minerals to help study x-ray properties. -
robert millikan
he used his oil- drop apparatus to measure the charge on an electron. he believed that the mass of an electron was at least 1000 times smaller than the smallest atom. -
niels bohr
created the bohr model of an atom. he was in a group of scientists that was working on the manhattan project. improved models saying that the atom has a positive nucleus that is surrounded by negative electrons. -
ernest rutherford
made an experiment using alpha particles that was fired at thin sheets of gold leaf. he concluded that the nucleus was surrounded by a large void before the encounterment of the electron cloud. -
louis de broglie
he predicted electrons wave nature and said that all matter has wave properties. -
werner heisenberg
he created the quantum mechanics theory. he discovered allotropic forms of hydrogen. -
Erwin Schrodinger
developed an atom model by combining equations for behavior of waves using the de broglie equation for the distribution of electrons in an atom. the electron is a wave trying to describe the areas in space where electrons can mostly be found. -
j.j thomson
J.J. Thomson discovered electrons and noticed that an atom can be divided. Also, he concluded atoms are made of positive cores and negatively charged particles within it. He developed the Plum Pudding Model before the atomic nucleus was discovered.
