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  (% abundance of isotope)(mass of isotope) –  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 10 23 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 n o & p + )

7. Problems How many grams are in 2.30 x 10 18 H 2 atoms?  (2.30 x 10 18 atoms)/(6.022 x 10 23 atoms/mole) = (2.3/6.022)(10 18 /10 23 ) = 0.382 x 10 18-23 mole = 3.82 x 10 -6 mol;(3.82 x 10 -6 mol)(2.01 g/mol)= 7.68  g How many atoms are in 3.50 mol Cu?  (3.50 mol Cu)(6.022 x 10 23 atom/mol) = 21.1 x 10 23 = 2.11 x 10 1 x 10 23 = 2.11 x 10 24 atom What is the mass in grams of 3.50 mol Cu?  (3.50 mol Cu)(63.55 gram/mol) = 222 g Cu