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History Democritus - First to use the term atom Aristotle - Defined matter as composed of hot, cold, wet and dry John Dalton - Modern Atomic Theory and Law of Multiple Proportions Antoine Lavoisier - Law of conservation of mass Joseph Proust - Law of Definite Proportions J.J. Thomson - Discovered the electron with cathode ray experiment and proposed Plum pudding model Robert Millikan - Discovered the charge/mass of the electron using Oil Drop Experiment Ernest Rutherford - Discovered the nucleus using gold foil experiment James Chadwick - Discovered the neutron Henri Becquerel - discovered radiation emitted by Uranium Marie Curie - discovered two other elements that emitted radiation (Polonium and Radium) Niels Bohr - Proposed energy levels and the Planetary model of the Atom Louis de Broglie - Proposed the wave particle duality of nature Werner Heisenberg - Proposed the Uncertainty Principle Erwin Schrodinger – Proposed electron cloud model (quantum mechanical model) of an atom John Newlands – noticed pattern when elements were arranged by atomic mass (repeated every 8th element). He used the word periodic to describe this pattern and named it the Law of Octaves Lothar Meyer – made a connection between atomic mass and properties of elements and made periodic table Dmitri Mendeleev– made a connection between atomic mass and properties of elements and made periodic table. Also predicted unknown elements. Henry Mosely – arranged periodic table by atomic number and gave us Periodic Law Four parts of an experiment Independent variable – what the scientist changes, what is being tested. Dependent variable – what changes because of the independent variable. Control – the comparison item, it is used to see if the independent has an effect (usually a sample with no independent used) Constants – everything else that is in the experiment that we keep constant 5 Branches of Chemistry Organic – Carbon containing compounds Inorganic – compounds that do not contain carbon Analytical – analyze compounds to determine composition Physical – combines chemistry with physical to explain what happens when reactions occur Biochemical – combines chemistry with biology to explain why life occurs on a molecular level