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

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

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

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

5. 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

6. 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

7. 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

8. 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 -.

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

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

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

12. 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

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

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

16. 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

17. 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.

18. 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?

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

20. 1247 =
4 sig figs
23896 =
5 sig figs
5.264 =

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

22. Significant Figures
Captive zeros (zeros b/w nonzero digits – – 4 captive zeros) are always significant
– 6 sig figs
sig figs

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

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

25. 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

26. Calculations w/ Sig figs
Adding/Subtracting: Add or subtract and record the least number of decimal places
=  = true answer

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