Chapter 1. Huh? 100% NATURAL 7- UP. Why Study Chemistry? aka Why are you here? Why Study Chemistry? aka Why are you here?

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1 Why Study Chemistry? aka Why are you here? Chapter 1 Chemistry: Matter and Measurement Huh? 1 Why Study Chemistry? aka Why are you here? What s the difference? Ethanol CH 3 CH 2 OH Methanol CH 3 OH Why Study Chemistry? aka Why are you here? 100% NATURAL 7- UP Now with NATURAL citric acid!! Natural Non-Natural Why Study Chemistry? aka Why are you here? Medicine Energy sources Materials Technology Food Agriculture Cooking Cars, clothes, computers, sporting goods 1

2 Scientific Method A systematic way to conduct research Define the problem Perform experiments and make observations Record data from experiment Interpret data Formulate/test hypothesis Summarize data (devise theory or law to explain phenomena) The Periodic Table On the periodic table, elements are located adjacent to other elements with similar general physical properties Metals usually solid at room temperature, lustrous, conduct electricity, malleable Non-metals solid, liquid, or gas at room temperature. Solids are brittle. Do not conduct electricity. Metalloids or Semi-metals shares properties of both metals and non-metals. Lustrous like metals, but brittle like non-metals Antimony. Looks like a metal, but is not a good conductor of electricity The Periodic Table Elements and the Periodic Table Groups (Families): columns. Divides elements into more closely related properties Periods: rows (we ll talk more about this relationship in later chapters) (Semi-metals) Elements and the Periodic Table Elements and the Periodic Table Alkali metals (react violently with water) Noble gases (very unreactive) Transition Metals Other Stuff Alkaline earth metals (less reactive than alkali metals) Halogens colorful, corrosive gases, liquids and solids Inner Transition Metals 2

3 Relative Abundances of elements On Earth Chemistry and the Elements Elements are not distributed evenly within the universe. In the Human Body H is 75% of mass of universe O, Si are 75% of the earth s crust O, C, H are more than 90% of the human body Fats Proteins (with N) Carbohydrates All contain O, C, H.. Some Chemical Properties of the Elements Intensive properties: do not depend on amount of material (freezing point, boiling point) Extensive properties: depend on amount of material (volume, mass) Physical properties: color, temperature, texture, odor, boiling point, melting point, conductance Chemical properties: reactivity; how an element reacts with other elements. (flammability, enthalpy of combustion) Physical and Chemical Changes Physical Changes: changing from one state to another. How elements are arranged does not change. How atoms are chemically bonded does not change. Chemical Changes: changes how elements are arranged with in matter. How atoms are chemically bonded does change. States of Matter Physical or chemical change? Physical and Chemical Changes Physical or chemical change? What has changed?

4 Which elements should I know? Need to know names and symbols: Elements 1-36 Groups 1, 2, 17, 18 Ag, Cd, Pt, W, Au, Hg, Sn, Pb, Sb, Bi SI Base Units Each physical quantity measured has its own SI base unit Volume meters cubed m 3 These are NOT the same m 3 = 1000L, cm 3 = ml liters l or L Remove the kilo when other prefixes are used SI Prefixes units Measurements Note: micro Mass is a Greek mu kg, g, mg, mm Length m, km, cm, mm, mm, nm Base unit Temperature K, o C, o F K = o C F = (9/5 * o C) + 32 o F C = 5/9 * ( o F 32) Need to be memorized Volume L = dm 3, ml = cm 3 Converting Prefixes Many times, we need to convert from one prefix to another. For example, how many kiloseconds (ks) are in 1 megasecond (Ms)? The fool-proof method mega = 10 6 kilo = 10 3 Converting Prefixes Short Cut: Move-the-decimal method Subtract the exponents. This determines how many places to move the decimal mega = 10 6 kilo = 10 3 Larger to smaller unit move to the right Smaller to larger unit move to the left Set-up the equation & cancel units 6 10 s 1Ms 1Ms 6 10 s 1ks 1Ms 3 1Ms 10 s 1ks 3 10 ks 3 10 s 6-3 = move 3 spaces 1Ms = 1 ks = ks = 1000 ks = 10 3 ks 4

5 Uncertainty in Measurement There is always uncertainty in measurement! Measurements are never exact. Different measuring devices have differing levels of precision and accuracy. Precision vs. Accuracy Describe each in terms of accuracy and precision How close repeated measurements are in respect to one another. Reproducibility. How close measurements are to the actual value. We use reference standards. Uncertainty in Measurement The temperature outside is o F. Several thermometers made by one manufacturer record the temperature as 67.8, 68.2, 67.2, 67.6, and 68.0 o F. How would you describe this data in terms of accuracy and precision? Significant Figures What are significant figures? Why are they important? When do you need to worry about them? How many decimal places can you use on the rulers below (shown in cm)? Would the price of the thermometers change your answer? 99 vs. $ Rules for Significant Figures Rules for Significant Figures All non-zero digits are significant (335 cm). Zeroes in the middle of a number are significant (3406 mg). Zeroes at the beginning of a number are NOT significant. Called leading zeros. ( km). Zeroes at the end of a number and after the decimal point are significant. Called following zeros. ( g). Zeroes at the end of a number and before the decimal point may or may not be significant (6890 ft). You will have to look at the measurement to determine this. Ambiguous. Not sure if the measurement to the 10 s or 1 s place. 5

6 Scientific Notation and Powers of tens Sometimes certain numbers, especially large or small numbers, are awkward to write cm A better way to write this is by using scientific notation How to write using scientific notation Scientific Notation and Powers of tens Write the following numbers in scientific notation and place in order of increasing value: 10 1 x 10-6 Remove all leading zeros Write all numbers after the first non-zero number x 10-5 Place the decimal after the first non-zero number Add x10 after the number Count how many spaces the decimal moves from its original location x x x x If the decimal point moves to the right, the exponent will be negative If the decimal point moves to the left, the exponent will be positive 32 Scientific Notation Practice How to Use Your Calculator Addition and Subtraction Combine numbers with same exponent and add numbers 7.4 x x 10 3 = 9.5 x 10 3 Multiplication Add exponents and multiply numbers 8.0 x 10 4 * 5.0 x 10 2 = 40 x 10 6 = 4.0 x 10 7 Division Subtract exponents and divide numbers 6.9 x 10 7 / 3.0 x 10-5 = 6.9/3.0 x 10 7-(-5) = 2.3 x To enter 1.00 x 10 4 in your calculator, DO NOT enter x or 10. Instead, use the exponent key ( EP or EE ). Press: 1.00 EP (or EE ) 4 Rule of thumb, EE and EP basically mean x10 within scientific notation. Significant Figures How many significant figures are in the following assuming they are measurements? Significant Figures in Calculations Don t round for sig. figs. until the END of all calculations. Keep extra sig figs between steps x Multiplication and division: report to the least number of significant figures. Ex: 2.8 x sig. figs. in answer = Addition and subtraction: report to the least number of decimal places. Ex: digits after decimal =

7 Significant Figures Practice Calculate the following using the correct number of sig figs: x ( ) x ( ) Be careful when you must use both rules in one calculation. Use one rule at a time Dimensional Analysis We use conversion factors convert from one uni to another unit. 1 dozen eggs = 12 eggs 1 inch = 2.54 cm 3 feet = 1 yard 1 Mm = 1x10 6 m 1dozen 12 eggs 1inch 2.54cm 3 feet 1 yard or or or 12 eggs 1dozen 2.54cm 1inch 1 yard 3 feet 1Mm 10 6 m 6 or 10 m 1Mm 38 Dimensional Analysis How many feet are in in? in 1ft 12 in ft How many feet are in cm? 1in 1ft cm ft 2.54 cm 12 in How many inches are in 52 km? More than one possible way to solve this problem: km m cm in km mi ft in Dimensional Analysis A cop clocks you going 4.47 x 10-2 km/s. Were you speeding? If so, are you going to jail? 1 mi = 1.61 km 60 s = 1 min 60 min = 1 hr Density Is density intensive or extensive? m density V If a steel ball bearing weighs 54.2 grams and has a volume of 6.94 cm 3, what is its density? If a steel beam is measured to have a volume of cm 3, how much does it weigh? 7

8 Volumes (cubed) and Areas (squared) If 1 in = 2.54 cm does 1 in 3 = 2.54 cm 3? So.(1 in) 3 = (2.54 cm) 3 1 in or 2.54 cm (1) 3 (in) 3 = (2.54) 3 (cm) 3 1 in 3 = cm 3 8