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Atoms

Atoms. 400 b.c. Greeks. Greeks philosophers ponder the nature of matter: what is it made of? Democritus: basic particle of matter = “atom” which means “ indivisble ”. Envisions these to be “ hard spheres” Aristotle: does not believe in atoms. Dalton’s Atomic Theory 1803.

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Atoms

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  1. Atoms

  2. 400 b.c. Greeks • Greeks philosophers ponder the nature of matter: what is it made of? • Democritus: basic particle of matter = “atom” which means “indivisble”. Envisions these to be “hard spheres” • Aristotle: does not believe in atoms

  3. Dalton’s Atomic Theory1803 1) All matter is composed of extremely small particles called atoms

  4. Dalton’s Atomic Theory1803 • Atoms of one element are all alike (size, mass)

  5. Dalton’s Atomic Theory1803 3) Atoms can’t be created, destroyed or subdivided

  6. Dalton’s Atomic Theory1803 • Atoms of different elements combine in simple whole number ratios to form compounds

  7. Dalton’s Atomic Theory1803 5) In a chemical reaction, atoms are combined, separated, or rearranged

  8. Conservation of massin chemical reactions

  9. Conservation of massin chemical reactions

  10. 1897 J.J. Thompson Cathode Ray Experiments The electron is discovered…. “PLUM PUDDING” model

  11. Rutherford’s Gold Foil Experiment1909 Ernst Rutherford bombards a piece of gold foil with positively charged alpha particles (the nucleus of a helium atom)

  12. Some alpha particles bounce back

  13. Rutherford’s Gold Foil Experiment Observations: • Most of the alpha particles passed straight through the gold foil as if it wasn’t even there! • The nucleus of the atom is small, dense, and positively charged

  14. Rutherford’s Gold Foil Experiment Interpretation (conclusions): • Atoms are mostly empty space and therefore MATTER is mostly empty space • Atoms have a small, dense, positively charged nucleus

  15. + + + This alpha particle passes through the atom’s empty space + + + Alpha particles have + charge two + charges will repel each other

  16. Subatomic Particles(Table O) Proton Electron Neutron

  17. Protons • Located in the atom’s nucleus • Positive charge +1 • Mass = 1 amu (Atomic Mass Unit)

  18. Neutrons • Located in the atom’s nucleus • zero charge (neutral) • Mass = 1 amu (Atomic Mass Unit)

  19. Electrons • Located in the electron cloud outside the nucleus • Negative charge -1 • Mass = 1/1836 amu (negligible)

  20. What are the subatomic particles in lithium and carbon?

  21. Models of the atom

  22. A model of the atom to scale • If YOU are the nucleus of an atom, your closest electron would be…. • ……..in downtown Rhinebeck!

  23. Actual image of 2 atoms

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