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Chapter 3

Chapter 3. Atoms: Basic Building Block of Matter. Atoms. Democritus coined term in 400 B.C. Dalton’s Atomic Theory Atoms compose all matter. An element’s atoms are identical is size, mass, & properties. {Didn’t know about isotopes}

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Chapter 3

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  1. Chapter 3 Atoms: Basic Building Block of Matter

  2. Atoms • Democritus coined term in 400 B.C. • Dalton’s Atomic Theory • Atoms compose all matter. • An element’s atoms are identical is size, mass, & properties. {Didn’t know about isotopes} • Atoms cannot be subdivided, created, or destroyed. {Didn’t know about fusion or fission} • Atoms of different elements combine in simple whole-number ratios. • Atoms combine/ separate/ rearrange in reactions

  3. Structure of Atom • Proton: 1 amu; (+) charge; Goldstein found it using cathode ray tube • Neutron: 1 amu; 0 charge; Chadwich • Electron: 0 amu; (-) charge; Thomson found it with cathode ray tube; Millikan measured charge & mass; Bohr proposed concentric electron orbitals • Nucleus: composed of protons & neutrons; Rutherford found it using gold-foil experiment

  4. Counting Atoms • Atomic Number = # of protons • # found in corner of element’s box on periodic table • Mass Number = # of protons + # of neutrons • Rounded value of mass below symbol on periodic table • Mass # minus Atomic # = # neutrons • Na’s atomic mass 23 [protons + neutrons] • minus atomic number 11 [ protons] • equals 12 [neutrons]

  5. Counting Atoms II • Average Atomic Mass = Weighted average of all naturally found isotopes of that element • S (% abundance of isotope)(mass of isotope) • S means “the sum of “ For oxygen: O-16 99.757% @15.994915 amu; O-17 0.038% @ 16.999132 amu; O-18 0.205 % @ 17.999160 amu (0.99757)(15.994915 amu)+ (0.00038)(16.999132) + (0.00205)(17.999160amu) = 15.9994053 amu

  6. Counting Atoms III • Molar Mass = grams/ mole • Noted on periodic table under the symbol of the element • Mole = same # of atoms of C-12 in 12 grams of C-12 • Avogadro’s number = 6.022 x 1023 particles/mole • Relative atomic masses • Noted on periodic table (Same # as the molar mass) • amu = atomic mass unit • 1 amu = 1/12 of C-12 mass (i.e., avg mass of no & p+)

  7. Problems • How many grams are in 2.30 x 1018H2 atoms? • (2.30 x 1018atoms)/(6.022 x 1023atoms/mole) = (2.3/6.022)(1018/1023) = 0.382 x 1018-23 mole = 3.82 x 10-6 mol;(3.82 x 10-6mol)(2.01 g/mol)= 7.68 mg • How many atoms are in 3.50 mol Cu? • (3.50 mol Cu)(6.022 x 1023 atom/mol) = 21.1 x 1023 = 2.11 x 101 x 1023 = 2.11 x 1024 atom • What is the mass in grams of 3.50 mol Cu? • (3.50 mol Cu)(63.55 gram/mol) = 222 g Cu

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