Chemistry01A_Lec2s-2010

Chemistry01A_Lec2s-2010 - Outline 2 Jan-7-2010 Check...

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Chem1A 1 Outline 2 Jan-7-2010 Check ilearn! Review Sig Figs and derived units Atomic Theory Background (Mass Laws) Atomic Structure Electrons, Nuclei, protons, neutrons (Thompson, Milliken, Rutherford) Nuclear Structure - A Z X, nuclides, isotopes, Symbols (X), atomic number (Z), mass number (A) SKILL: Write and interpret nuclide symbols
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Chem1A 2 Sig Fig Rules Significant -- Make sure that the measured quantity has a decimal point. -- Start at the left of the number and move right until you reach the first nonzero digit. -- Count that digit and every digit to it’s right as significant. Not significant: Zeros only identifying decimal point. Ex: (a) 0.00970 = 9.70*10 -3 (3 sig figs) (b) 2100. = 2.100* 10 3 (4 sig figs) (c) 2.1*10 3 (2 sig figs)
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Chem1A 3 14.0 g /102.4 mL = 0.136718 g/mL only three sig figs Sig Figs (example) 14.0 g /102.4 mL = 0.137 g/mL
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Chem1A 4 Rules for Significant Figures in Answers 1. For addition and subtraction . The answer has the same number of decimal places as there are in the measurement with the fewest decimal places. 106.78 mL = 106.8 mL Example: subtracting two volumes 863.0879 mL = 863.1 mL 865. 9 mL - 2.8121 mL Example: adding two volumes 83. 5 mL + 23.28 mL
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Chem1A 5 Derived Units SI derived units , combine SI base units. Volume ≡ length cubed, SI unit m 3 . Chemists use liter (L), volume unit = one cubic decimeter (dm 3 ). Speed - meters per second (m/s), miles per hours (mi/hr).
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Chem1A 6 Derived Units Density mass per unit volume of object d V m = Common mass unit is gram (g), and common volume unit is mL (liquids), cm 3 (solids), and L (gases) Mass = volume x density Volume = mass x 1 density
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Chem1A 7 Density example 1 PROBLEM: A stone weighs 12.4 g and has volume of 1.64 cm 3 . What is density of galena? Density = mass volume
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Chem1A 8 Density Example 2 PROBLEM: A piece of galena has volume of 5.6 cm 3 . If the density of galena is 7.5 g/cm 3 , what is the mass (in kg) of that piece of galena?
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9 Pay Attention to Units If the units are wrong, then your answers must be wrong! 3
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Chemistry01A_Lec2s-2010 - Outline 2 Jan-7-2010 Check...

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