Atomic Theory Reg

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  • Atomic Theory Reg

    1. 1. ATOMIC THEORY Building blocks of matter
    2. 2. In the beginning <ul><li>Empedocles: Earth, Fire, Water, Air </li></ul>
    3. 4. DEMOCRITUS <ul><li>IN 400 BC,DEMOCRITUS SAID: </li></ul><ul><li>ALL MATTER IS MADE UP OF TINY PARTICLES CALLED “ATOMOS” & empty space </li></ul><ul><li>Atoms are solid, homogeneous, indestructible and indivisible </li></ul><ul><li>Different kinds of atoms have different shapes and sizes </li></ul><ul><li>Different props. of matter due to size, shape and movement of atoms </li></ul><ul><li>Apparent changes in matter is result of changes of atom groupings </li></ul>
    4. 5. Aristotle <ul><li>One of the most influential philosophers </li></ul><ul><li>Disagreed with Democritus </li></ul><ul><li>Didn’t believe in “nothingness” of empty space </li></ul><ul><li>Set science back almost 2000 </li></ul><ul><li>yrs. </li></ul>
    5. 6. Antoine Lavoisier <ul><li>1743-1794; French chemist </li></ul><ul><li>Father of Modern Chemistry </li></ul><ul><li>Conservation of Mass </li></ul><ul><li>He established the consistent use of chemical balance </li></ul><ul><li>developed a new system of chemical nomenclature. </li></ul><ul><li>He was beheaded during the French revolution. </li></ul>
    6. 7. Joseph Proust <ul><li>1754 -1826; French chemist </li></ul><ul><li>Law of definite proportions </li></ul><ul><li>Compound always combines in the same whole-number ratio regardless of the size or source of the sample </li></ul>
    7. 8. John Dalton <ul><li>Teacher at age 12 </li></ul><ul><li>Loved meteorology </li></ul><ul><li>Law of Multiple Proportions </li></ul><ul><li>Atoms of different elements combine in different ratios to form different compounds </li></ul><ul><li>Ex: CO vs CO 2 </li></ul>
    8. 9. Dalton pictured compounds as collections of atoms. Here NO, NO 2 , and N 2 O are represented.
    9. 10. John Dalton (1766 – 1844) was an English scientist who made his living as a teacher in Manchester.
    10. 11. Dalton’s atomic theory <ul><li>1808 JOHN DALTON / ATOMIC THEORY </li></ul><ul><li>1. All matter is made up of atoms </li></ul><ul><li>2. Atoms of the same element are alike. </li></ul><ul><li>3. Atoms of different elements are different. </li></ul><ul><li>4. Compounds have a definite composition by weight and combine in small whole number ratios. </li></ul><ul><li>5. Atoms cannot be subdivided. </li></ul>
    11. 12. Subatomic Particles NUCLEUS ELECTRONS PROTONS NEUTRONS NEGATIVE CHARGE POSITIVE CHARGE NEUTRAL CHARGE ATOM Most of the atom’s mass. QUARKS Atomic Number equals the # of... equal in a neutral atom
    12. 13. Subatomic Particles <ul><li>Quarks </li></ul><ul><ul><li>component of protons & neutrons </li></ul></ul><ul><ul><li>6 types </li></ul></ul><ul><ul><li>3 quarks = 1 proton or 1 neutron </li></ul></ul>He
    13. 14. PARTICLES OF THE ATOM <ul><li>ELECTRON- JJ THOMPSON/1897 </li></ul><ul><ul><li>Mass/ Millikan </li></ul></ul><ul><ul><li>PROTON AND NUCLEUS- RUTHERFORD/ 1911 </li></ul></ul><ul><ul><li>ELECTRON SHELLS/ BOHR/ 1913 </li></ul></ul><ul><ul><li>NEUTRON-CHADWICK / 1932 </li></ul></ul>
    14. 15. Are Atoms Really Unbreakable? <ul><li>J.J. Thomson investigated a beam called a cathode ray </li></ul><ul><li>determined that ray was made of tiny negatively charged particles -- electrons </li></ul><ul><li>measurements led him to conclude that these electrons were smaller than a hydrogen atom </li></ul><ul><li>if electrons are smaller than atoms, they must be pieces of atoms </li></ul><ul><li>if atoms have pieces, they must be breakable </li></ul><ul><li>Thomson also found that atoms of different elements all produced these same electrons </li></ul>
    15. 16. Schematic of a cathode ray tube.
    16. 17. Thomson’s Plum Pudding Model <ul><li>Atom breakable!! </li></ul><ul><li>Atom has structure </li></ul><ul><li>Electrons suspended in a positively charged electric field </li></ul><ul><ul><li>must have positive charge to balance negative charge of electrons and make the atom neutral </li></ul></ul><ul><li>mass of atom due to electrons </li></ul><ul><li>atom mostly “empty” space </li></ul><ul><ul><li>compared size of electron to size of atom </li></ul></ul>
    17. 18. One of the early models of the atom was the plum pudding model.
    18. 19. Hantaro Nagaoka <ul><li>Japanese physicist </li></ul><ul><li>developed the “Saturnian” system in 1904 </li></ul><ul><li>resembled the planet Saturn, with rings of electrons surrounding a concentrated, massive positive charge </li></ul><ul><li>inherently unstable. By radiating continuously, the electron would gradually lose energy and spiral into the nucleus. </li></ul><ul><li>No electron could thus remain in any particular orbit indefinitely. </li></ul>
    19. 20. Robert Millikan <ul><li>Determined the charge of an electron </li></ul><ul><li>E- transferred from brass atomizer to oil droplets </li></ul><ul><li>Droplets fell thru. vacuum chamber </li></ul><ul><li>Calculated the charge on the droplet </li></ul><ul><li>Multiple of one small charge </li></ul>
    20. 22. Rutherford’s Gold Foil Experiment <ul><li>How can you prove something is empty? </li></ul><ul><li>put something through it </li></ul><ul><ul><li>use large target atoms </li></ul></ul><ul><ul><ul><li>use very thin sheets of target so do not absorb “bullet” </li></ul></ul></ul><ul><ul><li>use very small particle as bullet with very high energy </li></ul></ul><ul><ul><ul><li>but not so small that electrons will affect it </li></ul></ul></ul><ul><li>bullet = alpha particles, target atoms = gold foil </li></ul><ul><ul><li> particles have a mass of 4 amu & charge of +2 c.u. </li></ul></ul><ul><ul><li>gold has a mass of 197 amu & is very malleable </li></ul></ul>
    21. 23. Rutherford’s experiment on  -particle bombardment of metal foil.
    22. 24. Rutherford’s Results <ul><li>Over 98% of the  particles went straight through </li></ul><ul><li>About 2% of the  particles went through but were deflected by large angles </li></ul><ul><li>About 0.01% of the  particles bounced off the gold foil </li></ul>
    23. 25. (a) The results that the metal foil experiment would have yielded if the plum pudding model had been correct. (b) Actual results.
    24. 26. Rutherford’s Nuclear Model <ul><li>The atom contains a tiny dense center called the nucleus </li></ul><ul><ul><li>the volume is about 1/10 trillionth the volume of the atom </li></ul></ul><ul><li>The nucleus is essentially the entire mass of the atom </li></ul><ul><li>The nucleus is positively charged </li></ul><ul><ul><li>the amount of positive charge of the nucleus balances the negative charge of the electrons </li></ul></ul><ul><li>The electrons move around in the empty space of the atom surrounding the nucleus </li></ul>
    25. 27. Ernest Rutherford (1871 – 1937) was born on a farm in New Zealand.
    26. 28. Structure of the Nucleus <ul><li>The nucleus was found to be composed of two kinds of particles </li></ul><ul><li>Some of these particles are called protons </li></ul><ul><ul><li>charge = +1 </li></ul></ul><ul><ul><li>mass is about the same as a hydrogen atom </li></ul></ul><ul><li>Since protons and electrons have the same amount of charge, for the atom to be neutral there must be equal numbers of protons and electrons </li></ul><ul><li>The other particle is called a neutron </li></ul><ul><ul><li>has no charge </li></ul></ul><ul><ul><li>has a mass slightly more than a proton </li></ul></ul>
    27. 29. Bohr Model <ul><li>e - exist only in orbits with specific amounts of energy called energy levels </li></ul><ul><li>Therefore… </li></ul><ul><ul><li>e - can only gain or lose certain amounts of energy ( quanta ) </li></ul></ul><ul><ul><li>only certain photons are produced </li></ul></ul>
    28. 30. The Modern Atom <ul><li>We know atoms are composed of three main pieces - protons, neutrons and electrons </li></ul><ul><li>The nucleus contains protons and neutrons </li></ul><ul><li>The nucleus is only about 10 -13 cm in diameter </li></ul><ul><li>The electrons move outside the nucleus with an average distance of about 10 -8 cm </li></ul><ul><ul><li>therefore the radius of the atom is about 10 5 times larger than the radius of the nucleus </li></ul></ul>
    29. 31. A nuclear atom viewed in cross section.
    30. 32. Atomic models Dalton <ul><li>Thomson </li></ul><ul><li>Rutherford </li></ul><ul><li>Bohr </li></ul>H. Nagaoka

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