Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download The History of the Atom and Its Structure
Document related concepts
Transcript
Early History The Greeks in 400 B.C. proposed matter composed 4 fundamental substances: fire, earth, water & air. B. Early Philosophers believed matter was continuous could be divided infinitely C. Democritus Disagreed with early philosophers - small indivisible particles, called atomos _________ “Atoms” Whose theory was correct, Greeks or Democritus? unable to test theory - lack of equipment II. John Dalton (1766-1844) Developed modern atom theory using sci. meth. observed chem rxns hypothesis on reactant & product ratios developed theory, still mostly true! Dalton’s Theory 1 - Elements -tiny indivisible particles - atoms. 2 atoms of the same element are identical. 3 – Atoms of 1 element combine w/otherscompounds 4 - Chem rxns - atoms separated, joined, or rearranged Which statements are no longer true? SPLITTING THE ATOM Hydrogen-1 Hydrogen-2 Hydrogen-3 Lithium- Lithium- Carbon- Carbon- Nitrogen Carbon- Carbon How many Protons ? Electrons ? Neutron ? Nuclear Particles ? What are Isotopes? - average atomic mass is usually closest to the most abundant isotope - Elements w avg atomic mass close to whole numbers have only 1 isotope most elements occur as 2 or more isotopes. Sodium How many Protons? Electrons? Neutron? Nuclear Particles? III. Discovery - 3 subatomic particles Electron Proton Neutron He was also wrong about isotopes! A. Discovery of the electron: Sir. J. J. Thomson 2. How? +charged plate Cathode ray Negatively charged plate Cathode rays bent towards + charge repelled by plate with a (-) charge. concluded - cathode rays tiny (-) charged particles Thomson named particles: electrons negatively charged written e- Ernest Rutherford Gold-Foil Experiment 1910 used alpha rays & gold foil Rutherford’s Gold Foil Experiment alpha particles that have scattered alpha particles bouncing back alpha particles passing through the gold foil in a straight line What were the results? •alpha particles shot thru gold foil. •MOST particles passing directly thru •some bounced back Rutherford’s Conclusion •atoms have a very small dense region - a “nucleus” Which has most of the mass & a (+) charge rest - empty space w/ electrons the proton: E. Goldstein 1886 rays opposite direction of cathode rays Canal rays - + charged ions remain in gas proton is + charged (p+) James Chadwick After predicted by Rutherford 1920 the neutron : A Neutral particle, written as n0 Interesting Facts •If an atom was the earth, the nucleus radius would be only 60 m. •A pure copper coin penny contains about 2.4 x 1023 atoms. Earth’s population approx. 6 x 109. There are 4 x 1012 as many atoms in the coin as people on Earth. How small is the nucleus? • If the atom was the size of a football stadium, the nucleus would be an ant or sitting on the 50 yard line and the electron an ants foot traveling around the stadium • END V. Composition of an atom cont.. Smallest particle of element keeping properties -atom • Small dense nucleus w/ + charge. • Nucleus - neutrons & protons. •Most of mass in nucleus. • Electrons surround nucleus occupy most of the volume. Review: Atomic # = # of protons # of protons = # of electrons Mass # = Protons + Neutrons Neutrons = Mass # - Atomic # II. Average Atomic mass or amu the sum of protons & neutrons in the nucleus & the relative abundance of isotopes. Average Atomic mass is a decimal #. Atomic Number 11 Na Sodium Average Atomic Mass 22.990 What is C-12’s mass #, 12 or 12.01? What is carbon’s atomic mass, 12 or 12.01? Mass # Element Atomic # How many neutrons are in: 108 47 19 9 Ag F Neutrons = Mass # - Atomic # 19 – 9 = 10 neutrons Designate the atom, Chlorine, in the form of “symbol of element-mass #”. Cl - 35 D. Write the formula for the following isotopes of chlorine, Cl-35 & Cl-37. Determine the # of neutrons in each isotope of chlorine. Cl Cl 35 17 37 17 18 neutrons 20 neutrons IV. How is the average atomic mass of an element calculated? Mass of Formula: the isotope X % abundance of isotope expressed as a decimal 3. The mass of an electron 1916 - Robert Millikan found charge on electrons oil-drop experiment. calculated charge:mass ratio Emission spectrums • http://webmineral.com/help/FlameTest.shtml Chp 4 Quiz 1. What is Lithium’s symbol 2. Write Lithiums’ 2 isotopes, ex.12C6 3. List the 2 isotopes number of Protons, Electrons & Neutrons. 4. Which isotope is more common? 5. How do you know # 4 above? 6. About what % of Lithium weighs 7 7. Where is most of an atoms wt. 8. What occupies most of the volume of an atom. 5 THE ATOM REVIEW DOT • Proton Neutron Electron Mass Number Atomic # Neutrons 2. Anode Cathode Hertz Nucleus Quarks 3 Same as # of Protons Sodium does have 12 Was predicted by Chadwick It’s Positively Charged Is protons and neutrons Particles in a cathode ray has a positive & neutral charge the number of waves/sec Negatively charged electrode Positively charged electrode makes up protons and neutrons Bohr Chadwick found charge on electrons discovered nucleus Rutherford J.J. Thompson Millikin Mass/Charge ratio found something neutral determined atomic number Moseley Planetary model anode P+N cathode Freq. 3 in 1 VI. Instruments used to view atoms scanning electron microscope (SEM) can be used to view atoms SEM creates a 3D image. A scanning tunneling microscope views the atoms surface. 4.Avogadro Dalton Democritus Einstein Planck Abouaf Guy Lussac modern billiard ball 22.4 L of gas 6.02 x 10^23 No experiment-atoms indivisible energy relates to frequency mass changes to energy gases react in vol. proportion no great discovery YET! 5.Atomic mass based on Mass number of calcium Neutrons charge and Mass Electrons charge and Mass 0,1 carb-12 -1,0 40 6.Freq. of 100 MHz Wavelength 400nm, f =? 70%7.0 a.m.u., 20% 8 a.m.u. 10% 9.0 a.m.u. The energy of the above light is 6 protons eff. isotp 1/1800 20 neut. 3.0 7.5 7.4 _____ Joules work! Flame Test Spectrums Emission Spectrum - when an atom emits radiation when excited by heat/electric charge Na Cu K Ba Ca Sr Developed a spectroscope that focused the light from a burner flame onto a prism that separated the light into its spectrum. Studied the emission spectrum of several metals. 1855-1860 Robert Bunsen Gustav Kirchhoff For info on Xrays http://www.colorado.edu/physics/2000/quantumzone/lines2.html http://www.colorado.edu/physics/2000/xray/making_xrays.html 1885 - Johann Jacob Balmer (series) Analyzed the hydrogen spectrum & found that Hydrogen emitted 4 bands of light within the visible spectrum:
