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Atomic Theory

Atomic Theory. 460 - 370 B.C. Democritus. Matter made of small pieces that cannot be cut into smaller pieces. Pieces called atomos. 1776 – 1844 John Dalton. Introduced his ideas in 1803 Each element is composed of extremely small particles called atoms

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Atomic Theory

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  1. Atomic Theory

  2. 460 - 370 B.C. Democritus Matter made of small pieces that cannot be cut into smaller pieces. Pieces called atomos

  3. 1776 – 1844John Dalton Introduced his ideas in 1803 Each element is composed of extremely small particles called atoms All the atoms of a given elementare identical, but they differ from those of any other element Atoms are neither created nor destroyedin any chemical reaction A given compound always has the same relative numbers and kinds of atoms

  4. 1856 – 1940J. J. Thompson Discovered electron 1897 – Cathode Ray Experiment Plum Pudding model 1904 Electrons in a soupof positive charges Discovered isotopes 1913

  5. 1871 – 1937Ernest Rutherford Nucleus Theory 1910 alpha particle gold foil experiment An atom’s mass is mostly in the nucleus. Rest of the atom is mostly space. Positive charges in nucleus called protons Atom is like a cherry – seed is positive nucleus and pulp the space for electrons

  6. 1885 – 1962Niels Bohr Planetary Model 1913 Nucleus surrounded by orbiting electrons at different energy levels Electrons have definite orbits

  7. 1920sCloud Model Electrons not in orbits but in orbitals around the nucleus Electrons found in different areas depending on energy level

  8. 1932James Chadwick Modern model of atom Identified the neutron in the nucleus – no electrical charge Nucleus made up of protons and neutrons Protons and neutrons made up of quarks

  9. Smallest pieces of matter are called atoms • Democritus • Bohr • Rutherford • Dalton

  10. Each element has a different type of atom • Chadwick • Dalton • Rutherford • Democritus

  11. Atoms are neither created nor destroyed in a chemical reaction • Bohr • Rutherford • Dalton • Thompson

  12. Discovered that atoms contain negative charges – called them electrons • Chadwick • Rutherford • Democritus • Thompson

  13. Atom has a positive charge (proton) at its center (nucleus), but most of the atom is space • Democritus • Rutherford • Dalton • Bohr

  14. Electrons move around the nucleus in orbits, like planets around the Sun • Rutherford • Chadwick • Bohr • Dalton

  15. Nucleus not only contains protons but also neutrons that have no charge • Chadwick • Bohr • Rutherford • Democritus

  16. Protons and neutrons made of smaller parts called quarks • Bohr • Dalton • Rutherford • Chadwick

  17. Much of Dalton’s atomic theory is similar to what is believed today. What is one important difference between Dalton’s theory and present day theory?

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