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400
Greek Atomic Theory: Democritus-everything is composed of atoms
Democritus: everything is composed of atoms -
Period: 400 to
Atomic Theory TImeline
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Law of definite composition
A compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound. -
Law of multiple proportions
Applies to different compounds made from the same elements.
Mass ratio for one of the elements that combines with a fixed mass of the other element can be expressed in small whole numbers. -
Antione Lavoisier
Conservation of mass-total mass of a product of a chemical reaction is always same as total mass.Total mass of the products is the same as the sum of the masses of the reactants. Matter cannot be neither created nor destroyed, just rearranged. -
Law of Conservation of Mass
Matter cannot disappear it can only be rearranged, at high speeds mass changes to energy -
Joseph Louis Proust
created the law of constant composition -
Dalton's Atomic Theory
Oxygen and Carbon combined to make 2 compounds. ALL matter is made of invisible/indestructable atoms. Atoms of a given element are identical in their physical and chemical properties. Atoms of different elements have different physical/chemical properties. Atoms of different elements combine in simple, whole-number ratios to form chemical compounds. Atoms cannot be subdivided, created, or destroyed when they are combined, separated, or rearranged in chemical reactions. -
John Dalton
Recorded the 1st tables of relative atomic mass and the atomic number -
Law of Definite Proportions
If formula AB is constant then the weight ratio will stay the same -
Dmitri Mendeleev
Created the periodic table and the list of elements -
Eugene Goldstein
Investigated the X-rays and discovered the cathode rays -
Erwin Schrodinger
Created the Schrodinger equation that is used to describe the behavior of electrons in atoms -
Cathode Ray Tube
2 positive lead atoms connected into a neon tube will make it light up, electric makes light -
Plum Pudding Model
there has to be a positive and a negative charge to balance out the atom, atoms are neutral -
J.J Thompson
Discovered that cathode rays (applied the voltage across glass tubes which was sealed with various gases) are small steams of atoms and an electron has a negative charge. Implied that the ray was not a consequence of the gas, but rather an entity in and of itself. -
Marie Curie
Discovered the radioactive elements -
Rutherford Model
Model of nucleus and electrons, discovered that the nucleus is in the center and the electrons orbit it -
Ernest Rutherford
Discovered/studied alpha particles and discovered the positively charged nucleus. There must be something within the atom that must be massive as the particles being shot at it. -
Robert Milikan
Made the oil drop experiment which made electron have an electric charge -
Bohr Planetary Model
He thought that electrons only orbit in one direction, called stationary orbits. Electrons/planets in an atom can reside only in certain energy levels; the energy of an electron in an atom is quantized. -
NIels Bohr
Considered the term of stationary orbits for the electrons and that there is more than one level to orbit, also introduced the Electron cloud. "The electron in a hydrogen atom moves around the nucleus only in certain allowed circular orbits". Proposed that the energy of an electron in an atom is quantized. -
Henry Mosdeley
Numbered and ordered the elements -
Quantam Mechanical Model
Mathematical equation developed by Schrodinger, calculated where electrons are at any given moment -
Gold Foil Experiment
Showed that the nucleus is positive, and electrons orbit it -
James Chadwick
Found the neutron, and his discovery led to nuclear fission and the atomic bomb. The neutron is found in the nucleus with the proton. The mass of a neutron=mass of a proton. The neutron has no charge. -
Lise Meitner
FIrst discovered nuclear fission