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Chem

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  • 1. Chapter 4 History and Atomic Structure
  • 2. <ul><li>IDEAS: </li></ul><ul><ul><ul><li>He believed that matter was not divisible </li></ul></ul></ul><ul><ul><ul><li>He believed that matter was made up of tiny particles – atoms. </li></ul></ul></ul><ul><ul><ul><li>Properties of matter were due to the size and shape of the atoms. </li></ul></ul></ul><ul><ul><ul><li>Changes in matter were due to the grouping of atoms (not from changes within the atom) </li></ul></ul></ul><ul><li>PROBLEMS: </li></ul><ul><ul><li>He could not experiment, therefore he could not validate his ideas. </li></ul></ul><ul><ul><li>(For example, he could not explain what held the atoms together) </li></ul></ul>
  • 3. <ul><li>IDEAS </li></ul><ul><ul><ul><li>Questioned the idea that atoms moved through empty space. </li></ul></ul></ul><ul><ul><ul><li>He rejected the idea of atoms. </li></ul></ul></ul><ul><li>PROBLEMS </li></ul><ul><ul><li>Many people respected his ideas, therefore the atomic theory that was proposed 100 years earlier was rejected for the next 2000 years. </li></ul></ul>
  • 4. Obj. 1…Dalton’s Atomic Theory <ul><li>Four postulates (1808)... </li></ul>* * 2. Atoms of the same element are identical... each element is unique proton, neutron and electron isotopes exist <ul><li>Much of this theory is still accepted, </li></ul>with 2 exceptions 3. Atoms of different elements can physically mix or chemically combine (compounds). 1. All elements are composed of tiny, indivisible particles called ‘atoms’. 4. Chemical rxns. occur when atoms are separated, joined, or rearranged.
  • 5. Obj. 2…Atomic Scientists <ul><li>J. J. Thomson discovered electrons (e-) in 1897. </li></ul><ul><li>He passed an electric current through a glass </li></ul>tube filled with gas. <ul><li>He discovered that a beam of negative charges </li></ul>traveled from the cathode (-) to the anode (+).
  • 6. Obj. 2 cont... <ul><li>E. Goldstein discovered positive particles in atoms </li></ul>in 1886. <ul><li>He observed rays traveling in the opposite direction of </li></ul>cathode rays. <ul><li>These particles were termed ‘ protons’ (p + ) by Ernest </li></ul>Rutherford in 1920. <ul><li>His discovery was based on the fact that </li></ul>different atoms’ atomic mass and atomic # (# of protons) were not adding up. <ul><li>James Chaddwick discovered neutrons (n 0 ) </li></ul>in 1932.
  • 7. Obj. 2 cont... <ul><li>all e- carry exactly one unit of negative charge. </li></ul><ul><li>mass of an e- is 1/1840 the mass of a hydrogen atom (p + ). </li></ul><ul><li>Robert Millikan furthered Thomson’s work by describing </li></ul>the electron more in depth.
  • 8. Obj. 3 and 4…The Bohr-Rutherford Model 1. atoms are mostly space. (football arena) <ul><li>Ernest Rutherford conducted the famous ‘gold foil </li></ul>experiment’ (1911) which concluded that: 2. atoms have a solid nucleus at the center which contains most of the mass. <ul><li>This overturned the accepted ‘plum pudding model’ of the </li></ul>time.
  • 9. Obj. 3 and 4 cont... <ul><li>The Gold Foil Experiment... </li></ul><ul><li>Stats... </li></ul><ul><li>98% of particles went straight through (expected) </li></ul><ul><li>2% of particles deflected at large angles </li></ul><ul><li>0.01% of particles deflected straight back (canon balls & tissue!) </li></ul>(BBs and cream cheese!)
  • 10. Obj. 3 and 4 cont... <ul><li>The progression of the atom... </li></ul><ul><li>Why don’t the (-) e- fall into the (+) nucleus? </li></ul>Plum Pudding Rutherford Rutherford-Bohr Quantum <ul><li>After Rutherford’s findings, Niels Bohr further explained </li></ul>the atom by concentrating on the e- (1913). <ul><li>Bohr proposed that the e- travel on concentric </li></ul>orbits around the nucleus. <ul><li>Each orbit has a fixed energy (energy level) and e- do not </li></ul>lose energy.
  • 11. Obj. 5…Subatomic Particles PROPERTIES OF SUBATOMIC PARTICLES e- p + n 0 -1 +1 0 1/1840 1 1 9.11 x 10 -28 1.67 x 10 -24 1.67 x 10 -24 PARTICLE SYMBOL ELECTRICAL CHARGE RELATIVE MASS ACTUAL MASS (g) Electron Proton Neutron
  • 12. Obj. 6…Characteristics of Elements atomic # element symbol element name atomic mass K 19 Potassium 39.098
  • 13. Obj. 6 cont... <ul><li>Atomic # : </li></ul><ul><li># of p + in an atom </li></ul><ul><li>identifies element </li></ul><ul><li># p + = # e- in neutral atom </li></ul>(change atomic # = change of element). ** (+) charge = less e- than p + ** (-) charge = more e- than p + <ul><li>Atomic mass : </li></ul><ul><li>mass of the nucleus </li></ul><ul><li>p + + n 0 </li></ul><ul><li>units are a.m.u. (atomic mass unit) </li></ul>(a.k.a. mass #)
  • 14. Obj. 7…Atomic Symbols <ul><li>There are two ways to represent elements: </li></ul><ul><li>Symbol Form: </li></ul>OR <ul><li>Shorthand Form: </li></ul>name of element followed by atomic mass. <ul><li>Ex... </li></ul>Carbon - 14 Aluminum - 27 Nitrogen - 14 # X # atomic mass (# of p + ) atomic # element symbol # X atomic mass element symbol <ul><li>You can find mass #, atomic #, # of n 0 , and # of e- with </li></ul>either notation!
  • 15. Obj. 8…Atomic Calculations <ul><li>All mass of the atom is in the nucleus. </li></ul>- only p + and n 0 are in the nucleus. - if you know the mass of any atom, you can find the # of n 0 . <ul><li>Ex... </li></ul>element = _______________ atomic mass = ___________ atomic # = ______________ # of p + = _______________ # of n 0 = _______________ # of e - = _______________ Phosphorus 31 a.m.u.s 15 15 16 14 Manganese - 55 symbol = ______________ atomic mass = __________ atomic # = ____________ # of p + = ______________ # of n 0 = ______________ # of e - = ______________ Mn 55 a.m.u.s 25 25 30 25 31 P 15 +1 electrical charge on atom - if you know the # of n 0 and the # of p+, you can find the mass.
  • 16. Obj. 9…Isotopes - different # of n 0 !!! <ul><li>Three isotopes of Carbon: </li></ul>Carbon - 14 Carbon - 12 Carbon - 13 (6p + , 6n 0 ) (6p + , 7n 0 ) (6p + , 8n 0 ) <ul><li>Which of the following are isotopes of the same element? </li></ul>element of life extremely rare radioactive…carbon dating <ul><li>Note: atomic # will NEVER change in isotopes… </li></ul>only mass and # of n 0 do! 22 X 12 +3 22 X 10 25 X 10 -1 Neon - 20 Neon - 22 Fluorine - 20 <ul><li>Isotopes : atoms of the same element with different atomic </li></ul>masses .
  • 17. Obj. 10…Average Mass of Isotopes <ul><li>Isotopes are naturally occurring. </li></ul>- abundance of isotope is just as important as mass! <ul><li>Ex... </li></ul>Natural copper (Cu) consists of 2 isotopes ... Copper - 63 (mass = 62 .930 g/mole) Copper - 65 (mass = 64 .930 g/mole) 69% 31% <ul><li>To calculate avg. mass... </li></ul>mass x abundance for each isotope Step 1 : Step 2 : add the two values from step 1 together 62 .93 x .69 = 64 .93 x .31 = 43.42 20.13 43.42 20.13 + <ul><li>The mass # of an element (periodic table) is the weighted </li></ul>avg. of all isotopes that exist in nature. 63.55 g/mole
  • 18. Obj. 10 cont... <ul><li>Ex... </li></ul>Three isotopes of Oxygen: Oxygen - 18 Oxygen - 16 Oxygen - 17 99 . 759% 0.037% 0.204% <ul><li>The avg. mass (from P.T.) is closest to 16, therefore, </li></ul>Oxygen-16 is the isotope that is most abundant in nature. <ul><li>The average mass of an element is closest to the isotope </li></ul>that is most plentiful in nature.

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