CHEMISTRY = Chemistry is the study of matter and energy and the interactions between them

Studying science requires that one be a good observer. observationinference involves a judgment or assumption uses the five senses Observations

Data Observations are also called data. There are two types of data. qualitative dataquantitative data descriptions; measurements; no numbersmust have numbers and UNITS

How good are the measurements? Scientists use two word to describe how good the measurements are- Accuracy- how close the measurement is to the actual value. Precision- how well can the measurement be repeated.

Differences Accuracy can be true of an individual measurement or the average of several. Precision requires several measurements before anything can be said about it.

PRECISION VERSUS ACCURACY Problem : Identify if the following figures are either accurate or precise or both: A._________ B._________ C.__________ D._________ A ? Both A & P Only Precise Neither A/P

In terms of measurement Three students measure the room to be 10.2 m, 10.3 m and 10.4 m across. Were they precise? Were they accurate?

Data Must be organized Can be organized into charts, tables, or graphs

Line Graph shows continuous change Stock Price over Time

Elements of a “good” line graph axes labeled, with units use the available space title neat

How to read a graph Interpolate - read between data points What volume would the gas occupy at a temperature of 150 K? Extrapolate - read data beyond data points What volume would the gas occupy at a temperature of 260 K? Which do you have more confidence in? Why? (independent variable) (dependent variable) 7 L ~4 L

Line Graph Mass (g) Age (Year of Penny) Mass (g) Age (Year of Penny) Mass (g) Age (Year of Penny) Mass (g) Age (Year of Penny) How does the mass of a penny change with age? A B C D

Hypothesis A suggested solution to the problem. Must be testable Sometimes written as If…Then… statements Predicts an outcome

Scientific Law vs. Scientific Theory Law of Gravity A theory tries to explain why or how something happens. A law states what happens. Theory of Gravity Atomic Theory Collision Theory of Reactions

Significant Figures Numbers in science are used to measure Measurements can only be taken to the least precise level of the measuring device

, Significant Figures Counting Sig Fig Examples , sig figs, rule # 3 sig figs, rule # 2 sig figs, rule # Courtesy Christy Johannesson

Rounding rules Look at the number behind the one you’re rounding. If it is 0 to 4 don’t change it. If it is 5 to 9 make it one bigger. Round to four sig figs. to three sig figs. to two sig figs. to one sig figs

Watch the Sig Figs When rounding, you don’t change the size of the number. You should end up with a number about the same size (magnitude). Use place holders- they’re not significant. – Round to 3 sig figs – Round to 3 sig figs

Significant figures (cont’d) __________ 950.9__________ 0.08__________ 0.058__________ 8.097__________ 74.99__________ Round to the tenthsRound to the hundredths

# of sig figs in the answer is based on the # sig figs in least precise measurement. Which is the least precise? 7.22m or m Significant Figures Calculating with Sig Figs

Significant Figures Calculating with Sig Figs – Add/Subtract - The # with the lowest decimal value determines the place of the last sig fig in the answer. (This is the measurement that is the LEAST precise) 3.75 mL mL 7.85 mL 224 g g 354 g  7.9 mL  350 g 3.75 mL mL 7.85 mL 224 g g 354 g Courtesy Christy Johannesson

Significant Figures Calculating with Sig Figs – Multiply/Divide - The # with the fewest sig figs determines the # of sig figs in the answer. (This is the measurement that is the LEAST precise) (13.91g/cm 3 )(23.3cm 3 ) = g 324 g 4 SF3 SF Courtesy Christy Johannesson

MEASURING WITH ACCURACY AND PRECISION

Practice Measuring Length 4.5 cm 4.54 cm 3.0 cm Timberlake, Chemistry 7 th Edition, page 7 cm

How to measure Mass

How to Measure Volume Graduated Cylinder Come in variety of sizes measure milliliters

Meniscus - the curve the water takes in the cylinder How to Measure Volume l Meaure at the bottom of the meniscus.

The Metric System The units of measurement in science are from the metric system. The three most common are mass (grams), volume (liters), and length (meters) The metric system utilizes these base units then adds prefixes to indicate values increasing or decreasing by a factor of 10.

Converting khDdcm how far you have to move on this chart, tells you how far, and which direction to move the decimal place. The box is the base unit, meters, Liters, grams, etc

Converting khDdcm In order to convert from one unit to another, set up a proportion where the unknown (X) and the given (G) with their respective units of measurement are on top and the conversion factors are under in the right place

Metric Conversions 10cm =_____m 1mm =_____cm 10dL = _____mL 5 liters = _____mL

Metric Conversions 0.1dL =_____cL 1Kg = _____g 100 mm = _____cm 300,00mg = _____g

What about micro- and nano-? The jump in between is 3 places Convert μm to m Convert cm to nm k hDdcmμn

Scientific Notation

How wide is our universe? 210,000,000,000,000,000,000,000 miles (22 zeros) This number is written in decimal notation. When numbers get this large, it is easier to write them in scientific notation.

Powers of 10 cienceopticsu/powersof10/ cienceopticsu/powersof10/

Scientific Notation A number is expressed in scientific notation when it is in the form a x 10 n where a is between 1 and 10 and n is an integer

Write the width of the universe in scientific notation. 210,000,000,000,000,000,000,000 miles Where is the decimal point now? After the last zero. Where would you put the decimal to make this number be between 1 and 10? Between the 2 and the 1

2. 10,000,000,000,000,000,000,000. How many decimal places did you move the decimal? 23 When the original number is more than 1, the exponent is positive. The answer in scientific notation is 2.1 x 10 23

1) Express in scientific notation. Where would the decimal go to make the number be between 1 and 10? 9.02 The decimal was moved how many places? 8 When the original number is less than 1, the exponent is negative x 10 -8

Write in scientific notation x x x x 10 5

2) Express 1.8 x in decimal notation ) Express 4.58 x 10 6 in decimal notation. 4,580,000 On the graphing calculator, scientific notation is done with the button x 10 6 is typed

4) Use a calculator to evaluate: 4.5 x x Type You must include parentheses if you don’t use those buttons!! (4.5 x 10 -5) (1.6 x 10 -2) Write in scientific notation x 10 -3

5) Use a calculator to evaluate: 7.2 x x 10 2 On the calculator, the answer is: 6.E -11 The answer in scientific notation is 6 x The answer in decimal notation is

6) Use a calculator to evaluate (0.0042)(330,000). On the calculator, the answer is The answer in decimal notation is 1386 The answer in scientific notation is x 10 3

7) Use a calculator to evaluate (3,600,000,000)(23). On the calculator, the answer is: 8.28 E +10 The answer in scientific notation is 8.28 x The answer in decimal notation is 82,800,000,000

Write (2.8 x 10 3 )(5.1 x ) in scientific notation x x x x 10 11

Write in PROPER scientific notation. (Notice the number is not between 1 and 10) 8) x x ) x 10 4 on calculator: x 10 2

Write x 10 5 in scientific notation x x x x x x x 10 8