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Unit Objectives

Unit Objectives. 1)understand the evolution of models of the atom: Dalton, Thomson, Rutherford, Bohr, the ‘quantum model 2 ) understand the meaning of mass number, atomic (proton) number. 3) be able to write and work with full atomic symbols

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Unit Objectives

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  1. Unit Objectives 1)understand the evolution of models of the atom: Dalton, Thomson, Rutherford, Bohr, the ‘quantum model 2) understand the meaning of mass number, atomic (proton) number. 3) be able to write and work with full atomic symbols 4) be able to calculate relative atomic, molecular and formula mass

  2. Refreshing some Old Terminology • Bohr Rutherford Diagrams • Isotopes and ions • R.A.M. (Relative Atomic Mass)

  3. How can we know? 1.8 Mass spectrometer (SB p.20) Cl has 2 isotopes:Cl-35and Cl-37

  4. 1.8 Mass spectrometer (SB p.20) Mass spectrometer consists of 6 parts:

  5. 1.8 Mass spectrometer (SB p.21) Mass spectrum of Cl2:

  6. 1.8 Mass spectrometer (SB p.21) Mass spectrum of CH3Cl:

  7. ISOTOPES &AVERAGE ATOMIC OR MOLAR MASS

  8. 90.92 Abundance / % 8.82 0.26 19 20 21 22 23 m/z • MASS SPECTRA • R.A.M. • Consider neon and its 3 isotopes... 20Ne21Ne22Ne. • We use these values to determine the • average molar mass of an element or • Relative atomic mass, called RAM • Calculate the average relative atomic mass of neon using the above information. • Out of every 100 atoms 90.92 are 20Ne , 0.26 are 21Ne and 8.82 are 22Ne • Average = (90.92 x 20) + (0.26 x 21) + (8.82 x 22) = 20.179 • 100 • Relative atomic mass = 20.18

  9. Calculate the relative atomic mass of the following – give your answers to 3 significant figures Bromine : 79 Br 50% , 81 Br 50% Copper : 63 Cu 69% , 65 Cu 31% Zirconium : 90 Zr 51.5% , 91 Zr 11.2%, 92 Zr 17.1%, 94 Zr 17.4%, 96 Zr 2.8% Lead : 204 Pb 1.5% , 206 Pb 23.6%, 207 Pb 22.6%, 208 Pb 52.3% Neon : 20 Ne 90.9% , 21 Ne 0.2%, 22 Ne 8.9% 63.6 91.3 207. 20.2

  10. Can we calculate the % composition if we know the isotopes ? • Naturally occurring potassium consists of potassium-39 and potassium-41. • Calculate the percentage of each isotope present if the average is 39.1. • Assume there are x nuclei of 39K in every 100; so there will be (100-x) of 41K • so 39x + 41 (100-x) = 39.1 • 100 • therefore 39 x + 4100 - 41x = 3910 • thus - 2x = - 190 • and x = 95 • ANSWER There will be95%39K and • 5% 41K

  11. Right, ok now you try, see the handout

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