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History of the Atom
Democritus <ul><li>Proposed that all matter is  composed of tiny, indivisible particles called “ atomos” </li></ul><ul><li...
Dalton’s Atomic Theory (1807) <ul><li>1) Elements are made of tiny particles called atoms. </li></ul><ul><li>2) All atoms ...
Dalton’s Atomic Theory (cont.) <ul><li>Atoms of one element can combine with atoms of other elements to form compounds.  A...
Dalton’s Atomic Theory (cont.) <ul><li>5) Atoms are indivisible in chemical processes.  That is, chemical reactions do not...
Some of Dalton’s Symbols for the Elements
Sir William Crookes (1879) <ul><li>Invented the cathode ray tube and investigated electrical charges in gases. </li></ul>
Figure 3.7 :  Schematic of a cathode ray tube
John Joseph (JJ) Thomson (1903) <ul><li>Discovered the negatively charged particles ( 0 -1 e) </li></ul><ul><li>Proposed t...
Ernest Rutherford (1909) <ul><li>Discovered the positively charged dense central portion of the atom using his “gold foil ...
Figure 3.5 :  Rutherford’s experiment
Figure 3.6:   Results of foil experiment if Plum Pudding model had been correct
Figure 3.6 :  Actual Results.
Figure 3.9 :  A nuclear atom viewed in cross section
Niels Bohr (1913) <ul><li>Electrons are located in specific energy levels </li></ul><ul><li>Electrons move in a definite o...
James Chadwick (1932) <ul><li>Discovered the third subatomic particle (neutron) </li></ul><ul><li>Neutron has no charge an...
Figure 3.10 :  Two isotopes of sodium. Mass number ( A ) = protons + neutrons Atomic Number ( Z ) = protons A Z  X
An Ion of Sodium
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Notes Key History Of The Atom Teacher

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Notes Key History Of The Atom Teacher

  1. 1. History of the Atom
  2. 2. Democritus <ul><li>Proposed that all matter is composed of tiny, indivisible particles called “ atomos” </li></ul><ul><li>Today, we define an atom as the smallest part of an element that retains the chemical identity of that element </li></ul>
  3. 3. Dalton’s Atomic Theory (1807) <ul><li>1) Elements are made of tiny particles called atoms. </li></ul><ul><li>2) All atoms of a given element are identical. </li></ul><ul><li>3) The atoms of a given element are different from those of any other element. </li></ul>
  4. 4. Dalton’s Atomic Theory (cont.) <ul><li>Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms. </li></ul>
  5. 5. Dalton’s Atomic Theory (cont.) <ul><li>5) Atoms are indivisible in chemical processes. That is, chemical reactions do not create or destroy atoms, they simply change the way the atoms are grouped together. </li></ul>
  6. 6. Some of Dalton’s Symbols for the Elements
  7. 7. Sir William Crookes (1879) <ul><li>Invented the cathode ray tube and investigated electrical charges in gases. </li></ul>
  8. 8. Figure 3.7 : Schematic of a cathode ray tube
  9. 9. John Joseph (JJ) Thomson (1903) <ul><li>Discovered the negatively charged particles ( 0 -1 e) </li></ul><ul><li>Proposed the “plum pudding model” </li></ul><ul><li>Postulated the positive particles </li></ul>
  10. 10. Ernest Rutherford (1909) <ul><li>Discovered the positively charged dense central portion of the atom using his “gold foil experiment” </li></ul><ul><li>1 1 p </li></ul>
  11. 11. Figure 3.5 : Rutherford’s experiment
  12. 12. Figure 3.6: Results of foil experiment if Plum Pudding model had been correct
  13. 13. Figure 3.6 : Actual Results.
  14. 14. Figure 3.9 : A nuclear atom viewed in cross section
  15. 15. Niels Bohr (1913) <ul><li>Electrons are located in specific energy levels </li></ul><ul><li>Electrons move in a definite orbit around the nucleus </li></ul>
  16. 16. James Chadwick (1932) <ul><li>Discovered the third subatomic particle (neutron) </li></ul><ul><li>Neutron has no charge and a mass of ~1 amu </li></ul><ul><li>1 0 n </li></ul>
  17. 17. Figure 3.10 : Two isotopes of sodium. Mass number ( A ) = protons + neutrons Atomic Number ( Z ) = protons A Z X
  18. 18. An Ion of Sodium

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