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10/5-6 Starter

10/5-6 Starter. A neutral atom contains 34 electrons and has an A of 59. Write the nuclear symbol notation and hyphen notation for this isotope. Ch. 3 Atoms. 3.3 Counting Atoms. Relative Atomic Mass.

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10/5-6 Starter

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  1. 10/5-6 Starter A neutral atom contains 34 electrons and has an A of 59. Write the nuclear symbol notation and hyphen notation for this isotope.

  2. Ch. 3 Atoms 3.3 Counting Atoms

  3. Relative Atomic Mass • since masses of atoms are so small, it is more convenient to use relative atomic masses instead of real masses • to set up a scale, we have to pick one atom to be the standard • since 1961, the carbon-12 nuclide is the standard and is assigned a mass of exactly 12 amu

  4. Relative Atomic Mass • atomic mass unit (amu)- one is exactly 1/12th of the mass of a carbon-12 atom • mass of proton= 1.007276 amu • mass of neutron= 1.008665 amu • mass of electron= 0.0005486 amu

  5. Relative Atomic Mass • the mass number (A) and the relative atomic mass are very close but not the same because • relative atomic mass includes electrons • the proton and neutron masses aren’t exactly 1 amu

  6. Average Atomic Mass • weighted relative atomic masses of the isotopes of each element • each isotope has a known natural occurrence (percentage of that elements’ atoms)

  7. Calculating Average Atomic Mass • Naturally occurring copper consists of: • 69.71% copper-63 (62.929598 amu) • 30.83% copper-65 (64.927793 amu) (0.6971 x 62.929598)+(0.3083 x 64.927793) =63.55 amu

  8. Calculating Average Atomic Mass • An element has three main isotopes with the following percent occurances: • #1: 19.99244 amu, 90.51% • #2: 20.99395 amu, 0.27% • #3: 21.99138 amu, 9.22% • Find the average atomic mass and determine the element.

  9. Calculating Average Atomic Mass Neon

  10. The mole • a unit for measuring a very large amount- like number of atoms or molecules in a sample • like one dozen (1 dozen = 12 things) • except bigger: 1 mole = 6.022x1023 things • Why 6.022x1023 ? • 6.022x1023 is the number of atoms in exactly 12 g of carbon-12

  11. The mole • 6.022x1023 is called Avogadro’s Number in honor of all of his contributions to chemistry • can be used as a conversion factor between a number of things and mole

  12. Molar Mass • the mass of one mole of pure substance in grams per mole • numerically equal to average atomic mass • under the symbol on the periodic table • can be used as a conversion factor between moles and grams

  13. Conversion Factors # Atoms Grams Moles Use Molar Mass: grams per mole Use Avog.’s Number: atoms per mole

  14. C = 12 x 6 = 72 • H = 1 x 12 = 12 • O = 16 x 6 = 96 • 180 g/mol

  15. Gram  Moles • use molar mass • Ex. 32.3 g Na = ? mol Na • Ex. 0.56 mol Fe = ? g Fe

  16. # Atoms  Moles • use Avogadro’s Number • Ex: 1.40 mol Na = ? Na atoms • Ex: 3.4x1023 atoms Fe = ? mol Fe

  17. Grams  # Atoms • use both: Avogadro’s # and molar mass • Ex: 0.0326 g N = ? atoms of N • Ex: 2.01x1041 atoms of H = ? g H

  18. Mass  Atom Conversion Practice • How many grams are in 1.50 X 10 23 atoms of Na? • How many grams are in 6.02 X 10 23 atoms of Oxygen? • How many atoms are in 35 grams of Lithium? • How many atoms are in 24 grams of C?

  19. Mass  Atom Conversion Practice • 5.73 g Na • 15.99 g O • 3.05 x 10 24 atoms Li • 1.20 x 10 24 atoms C

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