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465
Democritus
Ancient Greek philosopher who advocated the atomic theory of matter in 465 BC. He imagined starting with a large piece of matter and gradually cutting it into smaller and smaller pieces, finally reaching the smallest piece. This tiniest building block that could no longer be cut . The atoms Democritus envisioned differed only in shape and size. In his theory, different objects looked different because of the way the atoms were arranged. -
John Dalton
Daltons theroy was:
1) All matter is made of atoms. Atoms are indivisible and indestructible. 2) All atoms of a given element are identical in mass and properties. 3) Compounds are formed by a combination of two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of atoms.
-Formalized the discovery of Lavoisier into the "Law of Definite Proportions:" When atoms combine to form a particular compound, they always combine in the same ratios by weight. -
Ernest Rutherford
Was a man from New Zealand who did the famous and well-known "gold foil experiment" which disagreed with the J.J. Thompson's plum pudding model of the atom and proved that all atoms have a small, positively charged nucleus and the rest of the atom is made up of mostly empty space. -
J.J. Thomson
Thomson discovered the electron in 1897. The theory said that atoms as a whole were neutrally charged. This was known as the Chocolate Chip Cookie Model because the electrons are like the chocolate chips embedded into the cookie and the dough is like the cloud of positive particles surrounding the chocolate chips(electrons). The Crooke's tube experiment showed J.J. Thomson that there were electrons in an atom. This experiment also showed him that electrons were negatively charged. -
Henri Becquerel
While studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously decompose and give off very pentrating rays. He discovered radioactivity by doing many experiments. He kept a diary that showed all his experiments thats was proven true. -
Maria & Pierre Curie
They did work in the investigations of radioactivity. Marie is the first woman to win a Nobel Prize. They discovered Polonium and Radium - the latter named for the radioactive glow visible in the dark. With numerous experiments Marie confirmed Becquerel's observations that the electrical effects of uranium rays are constant. -
Robert Millikan
Discover that the mass of a hydrogen atom is equal to the charge of an electron and the mass of an electron. The oil drop experiment was an experiment performed by Robert Millikan and Harvey Fletcher in 1909 to measure the elementary electric charge (the charge of the electron). -
Niels Bohr
He worked on the Manhattan Project which constructed the fist atomic bomb an he increased our modern knowledge of the structure of the atom. Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of sucessive orbital shells of electrons. -
Quantum model
The quantum theory is the most up-to-date theory of the times. Its model of the atom explains its stability and like Bohr's Model, treats atoms as electrons surrounding a nucleus. The wave-particle duality of quantum theory allows electrons to be described as waves, instead of particles. The double-slit experiment, sometimes called Young's experiment, is a demonstration that matter and energy can display characteristics of both waves and particles. -
James Chadwick
James Chadwick descovered the neutron and proved that the atomic nucleus contained a neutral particle which had been proposed more than a decade earlier by Ernest Rutherford. In 1935, Chadwick received the Nobel Prize for Physics for this discovery. During World War II, he worked with the British atomic bomb project. -
Aristotle
In 384 BC Aristotle, one of the most influential philosophers of that time, believed in some kind of "smallest part" of matter but not with Democritus's descriptions. Aristotle developed the theroy that all matter consisted of four elements: Earth, Air, Water and Fire. There were also four qualities: dryness, hotness, coldness, and moistness. Fire was dry and hot, water was moist and cold, etc. Aristotle's theory was used for almost 2000 years, until after the scientific revolution.
