Units 1: Introduction to Chemistry Chapter 3.1 Pages 63-72

What clothes would you wear to school if the temperature was 22 degrees? If I told you I weighed 120 am I overweight?

Measurement Measurement is both a number and a unit. The measurements we use in science is of the International system of measurements (SI)

Measurement To deal w/ very large and very small numbers we use scientific notation 602000000000000000000000 or 6.02 X 1023

Measurement A number in scientific notation has 2 parts The coefficient which is b/w 1 and 10 The exponent: (X 10n) n= the number of times you move the decimal/ the number of times you multiply the new number

Measurement Lets put 125 into Scientific notation; 1. Place a decimal in the number to make it a number b/w 1 and 10 125.  1.25

Measurement 2. How many places did you move the decimal? 125.  1.25 2 125.  1.25 2 -3. Now place the number 2 as the exponent

Measurement 4. If the original number was greater than 1 the exponent is +, if the original number is less than 1 (.00125) than the exponent is -.

Measurement So…. 125.  1.25 X 102 Try 87.073 8.7073 X 101

Measurement Now try the other direction 1.00 X 105 105 = 100000 so multiply 1.00 X 100000 or move the decimal 5 places. The 5 is positive so make the number bigger. = 100000

Measurement Try these on the mini boards 4 X 102 400 5 X 10-6 .000005

Measurement When multiplying exponents you add the exponent When dividing you subtract the exponent 2.865 X 104 X 1.47 X 103 = 4.21 X107

Significant Figures Accuracy: How close a measurement comes to the actual true value Precision: How close the measurements are to one another

Significant Figures Sig figs are the amount of decimal places that are in a number in order to make the number accurate and precise.

Significant Figures Measurements must be precise and accurate All instruments have a specific # of sig fig. Be sure to read to the correct # of sig figs

Significant Figures To read the correct # of sig figs you must record all the numbers you can read from the instrument plus one additional number that is estimated.

How would you read these rulers. Which is more precise How would you read these rulers? Which is more precise? Use the mini board Which ruler is more uncertain?

Significant Figures Rules for sig figs 1. Nonzero integers = always significant

1247 = 4 sig figs 23896 = 5 sig figs 5.264 =

Significant Figures 2. Zeros: 3 classes Leading zeros (zeros before nonzero digits – 0.00013 – 4 leading zeros) are never significant just place holders 0.00013 – 2 sig figs 0.0256 – 3 sig figs

Significant Figures Captive zeros (zeros b/w nonzero digits – 4.00002 – 4 captive zeros) are always significant 1.00002 – 6 sig figs 5.0236 5 sig figs

Significant Figures Trailing zeros (zeros at the end of # - 1100 – 2 trailing zeros) significant only if # has a decimal. 1100 – 2 sig figs 1100. – 4 sig figs 5.2300 – 5 sig figs

Significant Figures Exact #: # not obtained through measurements have unlimited sig figs 3 pies 22 students 1” =2.54 cm (given)

Rounding Last # less than 5 - # prior stays the same 1.24 = 1.2 Last # equal to or greater than 5 - # prior increases 1.25 =1.3 5467 = 5470

Calculations w/ Sig figs Adding/Subtracting: Add or subtract and record the least number of decimal places 15.86 + 22.0 + 2.0085 = 39.8685  39.9 = true answer

Calculations w/ Sig figs Multiplying/Dividing – multiply or divide and record the least # of sig figs 2.35 X 2.5 = 5.875  5.9 is true answer. 2 sig figs is the limiting term.