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Period: 460 BCE to 370 BCE
Democritus
Contributions
-Matter is composed of atoms, which move through empty space.
-Atoms are solid, homogeneous,indestructible, and invisible.
-Different kinds of atoms have different sizes and shapes.
-Size, shape, and movement of atoms determine the properties of matter. -
Period: 384 BCE to 322 BCE
Aristotle
Contributions
-Empty Space Cannot Exist.
-Matter is made of earth, fire, air, and water. -
Period: to
Anton Lavoisier
Contributions
-Father of Chemistry
-Disproved phlogiston theory by showing that oxygen was a major part in combustion
-Discovered that no chemical mass is lost in a chemical reaction (Law of Conservation of Mass) -
Period: to
Dalton
Contributions
-Developed hypothesis that atoms are a type of solid sphere. Four primary statements in his theory: atoms make up all matter, atoms join to form compounds, & that within the same mass, all atoms are identical and indivisible.
-Matter is composed of extremely small particles called atoms.
-Atoms of a given element are identical in size, mass and chemical properties.
-Atoms of a specific element are different from those of another element. -
Period: to
Sir J.J. Thompson
Contributions
-Determined the charge -to- mass ratio
-Concluded that the mass of the charged particle was much less than that of a hydrogen atom
-Plum Pudding Model-atom is a sphere of positively and negatively charged electrons that balance the total positive charge. -
Period: to
Robert Millikan
Contributions
-Determined the charge of an electron using the oil drop apparatus
-Determined that the magnitude of the charge on each drop increased in discrete amounts and determined that the smallest common denominator was 1.602x10*-19
-Calculated the mass of an electron -
Period: to
Sir Ernest Rutherford
Contributions
-Was the first to split the atom
-Awarded the Nobel Prize in Chemistry for atomic structure theory
-Called "Father of the Nuclear Age"
- His atomic model describes the atom as a tiny dense positively charged core called a nucleus -
Period: to
Albert Einstein
Contributions
-Created Theory of Relativity
-Originated Quantum Theory
-Created Theory of Critical Opalescence
-Nobel Prize in Physics
-Einsteinium is the element named for him
-Considered by many to be the most influential scholar of all time -
Period: to
Niels Bohr
Contributions
-Great contribution to modern physics was the atomic model
-The Bohr Model shows the atom as a small, positively charged nucleus surrounded by orbiting electrons.
-First to discover that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element
-The chemical elements Bohrium is named for him. -
Period: to
Erwin Schrodinger
Contributions
-Contributed to the theory of Quantum Mechanics
-Discovered that life feeds on negative entropy
-Thought that genetic information was stored in molecules and this thought caused Watson and Crick to eventually discover DNA.
-Electron Cloud Model-describes where electrons are when they go around the nucleus of an atom. -
Period: to
Sir James Chadwick
Contributions
-Discovered the neutron
-Neutron discovery lead to eventual creation of neutron bomb
-Was a leading advocate for creating atomic bomb -
Period: to
Friedrich Hund
Contributions
-Made contributions to Quantum Theory about atom structure and structure of molecular spectra
-Hund's Rules named for him (electron configuration, spectroscopy, and quantum chemistry) -
Period: to
Wolfgang Pauli
Contributions
-Pioneer of Quantum Physics
-Formulated "Pauli Principle"- no two electrons in an atom can have identical sets of quantum numbers -
Period: to
Otto Hahn, Lise Meitner and Fritz Strassmann
Contributions
-Each worked on separate experiments that made them partially responsible for the discovery of fission.
-Found that if you attack elements with neutrons, most will have some change but Uranium will split in half and each new piece will become radioactive.
-Discoveries lead to formation of the Manhattan Project -
Period: to
The Aufbau Principle
Electrons orbiting one or more atoms fill the lowest energy levels first before filling higher ones. This makes electrons more stable.