Week 2 Chemistry Notes
Week 2 Chemistry Notes CHEM 1127Q-011
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This 3 page Class Notes was uploaded by Amelia on Thursday September 8, 2016. The Class Notes belongs to CHEM 1127Q-011 at University of Connecticut taught by Dr. Cady in Fall 2016. Since its upload, it has received 42 views. For similar materials see General Chemistry in Chemistry at University of Connecticut.
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Date Created: 09/08/16
9/7 CHAPTER 1 Essential Ideas (cont.) Measurement (cont) 1) The goal is to be accurate and precise a) Accuracy: the degree to which the result of a measurement, calculation, or specification conforms to the correct value or a standard. b) Precision: the degree to which the results are similar (how often you get the same number) Scientific Notation 1) A method for writing numbers that is more pre−6se and often shorter a) Example: .0000025 = 2.5 × 10 2) Significant Figures a) The numbers we know precisely b) Zeros in Significant Figures i) Zeros in the middle of numbers are significant. Zeros after a real number and decimal point are real. (1) example: 203 = 3 significant figures (2) example: 1.003 = 4 significant figures ii) Zeros before a decimal point are real. (1) example: 2000.0 = 5 significant figures iii) Zeros are not significant when real numbers follow the zeros and the decimal place. (1) example: 0.00002 = 1 significant figure iv) Zeros are not significant after a real number without a decimal point. (1) example: 500 = 1 significant figure 3) Exact Numbers a) Exact counting of discrete thing. For example, 12 eggs are countable, simply 12. 4) Significant Figures in Math a) Multiplication and division i) Take least number of significant figures (1) example: 10.0÷ 3.3333 = 3.33 33 → 3.33 b) Addition and subtraction i) Take the least number of decimal places (1) example: 15624 + 1.02 = 15625 .02 → 15625 c) Multiple step equations i) Do the stuff in parentheses “(...)” first ii) Don’t round until the end! (1) example: (2.0×5.01) 0.002 (2) (2.0×5.01) = 10.02 (3) 10 .02 0.002 = .018 → 10 Converting Between Units 1) Always write out all units 2) Cancel units as you go. All units must cancel or be in your product! a) Example: 2.0km/g → ?m/g b) 2.0km/g • ( −3 ) 2.0 g •( 1−3 )• m → 2.0 m/g (10 ) 3 10 kg 10 c) 2.0 × 10 m/g 3) Units Raised to a Power a) When you have a unit like cm and you want to convert it to ft you may need to adjust your conversion factor b) Example: Credit https://www.chem.tamu.edu/class/fyp/mathrev/mrda.html 4) Temperature Units a) Fahrenheit water freezes at 32° and boils at 212° based on salt water freezing at 0° and 100° being around body temperature. b) Celsius water freezes at 0° and boils at 100° c) Kelvin absolute zero is 0° d) Formulas: i) C° = (°F32)/1.8 ii) F° = °C× 1.8 + 32 (1) Example: convert 80°F into Celsius (2) (80°32°)/1.8 = (3) 48 °/1.8 = 6.6666 → 30° Celsius iii) K = °C + 273.15 (1) Example: 77K in °C (2) 77273 . 15 = 196.15 → 196° Celsius iv) °C = K 273.15 CHAPTER 2 Atoms and Elements The Atom 1) History a) John Dalton i) Established Atomic Theory around 1800 ii) Atom the smallest unit of an element that can not be divided and remain himself iii) Atomic Theory (1) Atoms of different elements have different masses (2) Different combinations produce different compounds (3) Atoms cannot be created or destroyed b) JJ Thomson and Ernest Rutherford i) Used a cathode ray to discover negatively charged particles in atoms called electrons. c) Rutherford Backscattering i) Used a beam of alpha particles aimed a piece of gold foil. Most of the atoms went through the foil, with some small deflections, leading to the discovery of empty space in atoms. 2) Atoms are made up of protons, neutrons and electrons. a) Protons and neutrons reside in the nucleus b) Electrons revolve around the nucleus in a ‘cloud’
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