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ATOMIC THEORY ATOMIC STRUCTURE ATOMIC THEORY DEMOCRITUS - 400BC PROPOSED THE FIRST ATOMIC THEORY. HE SUGGESTED THAT THE WORLD WAS MADE OF TWO THINGS, EMPTY SPACE AND TINY PARTICLES HE CALLED ATOMS. ATOMIC THEORY JOHN DALTONDEVELOPED THE FIRST MODERN ATOMIC THEORY ATOMIC THEORY ALL MATTER IS COMPOSED OF VERY SMALL PARTICLES CALLED ATOMS ATOMS CANNOT BE BROKEN DOWN INTO SMALLER PARTICLES. ALL ATOMS OF AN ELEMENT WERE EXACTLY ALIKE AND ATOMS OF DIFFERENT ELEMENTS ARE QUITE UNLIKE. ATOMS CAN UNITE WITH OTHER ATOMS IN SIMPLE RATIOS TO FORM COMPOUNDS ATOMIC THEORY ANTOINE LAVOSIER-CONDUCTED AN EXPERIMENT THAT PROVED THE LAW OF CONSERVATION OF MASS JOSEPH PROUST-OBSERVED THAT SPECIFIC SUBSTANCES ALWAYS CONTAIN ELEMENTS IN THE SAME RATIO BY MASS. THIS PRINCIPLE IS KNOWN AS THE LAW OF DEFINITE PROPORTIONS (COMPOSITION) ELECTRON DISCOVERY JJ THOMSON-1897 DID SOME SKILLFUL RESEARCH ON CATHODE RAYS. AS A RESULT HE IS GENERALLY CREDITED WITH THE DISCOVERY THAT THE RAYS CONSIST OF ELECTRONS. EARLY RESEARCH ON ATOMIC PARTICLES Robert Millikan- Obtained the first accurate measurement of an electron’s charge. The Oil Drop Experiment EARLY RESEARCH ON ATOMIC PARTICLES Rutherford-discovered the proton using cathode ray tubes and alpha particles. James Chadwick- Credited with the discovery of the neutron. ISOTOPES AND ATOMIC NUMBER JJ Thomson – observed what seemed to be two kinds of neon atoms, chemically alike but different in mass. Atoms of the same element that differ in mass are called isotopes. Isotopes have the same number of protons but different numbers of neutrons. NEON ISOTOPES ISOTOPES AND ATOMIC NUMBER Henry Moseley- Studied x-rays produced in x-ray tubes with different metal anodes. The wavelength depends on the number of protons in the nucleus and is always the same for a given element. The number of protons in an atom is called the atomic number.(Z) ATOMIC STRUCTURE Neils Bohr – Proposed the Planetary Model of the atom. NUCLEAR THEORY OF THE ATOM 1912-1913 Rutherford brought together a brilliant team of physicists whose experiments revealed the modern structure of the atom. The Nuclear Theory of the Atom Nuclear Theory Geiger and Marsden-Members of the team of Physicists brought together by Rutherford who conducted the Gold-Foil Experiment. THE THREE MAIN SUBATOMIC PARTICLES