1. Introductory Chemistry
Dr. George Lessard

2. Handling Numbers and Units
Chapter 2
Chemistry 101
Lecture 2
Dr. George Lessard

3. Since Chemistry deals with matter, chemists measure
Everybody thinks the more decimals the better
Think about global warming
Is it really getting warmer?
And does it make a difference?

4. Atoms are very small, The Universe is very big
Chemistry needs to measure very small numbers and very big numbers!
How many zeros can you remember?

5. Exponents are one way of not having to count zeros
Any number can be expressed as the product of a natural number and and exponent
300 = 3 x 102
N x (base 10)x

6. Any number, big and complex
Look at the number, remember it can be broken down into pennies, dimes and dollars, how many dollars, how many dimes and how many pennies

7. Or small and simple Take the number. Move the decimal
If moving the decimal makes the natural number smaller then the exponent must get bigger to make the number the same
If moving the decimal makes the natural number bigger then the exponent must get smaller to make the number the same

8. There are many ways of expressing exponents, but!
Scientists only use one method - SCIENTIFIC NOTATION
In Scientific Notation there is only one number to the left of the decimal!
Learn to use Scientific Notation

9. Skillbuilders
Skillbuilder 2.1 Scientific Notation
The total U.S national debt in 2010 was approximately $12,102,000,000,000. Express this number in scientific notation.
Skillbuilder 2.2 Scientific Notation
Express the number in scientific notation.
1Point Quiz- write it down without looking it up-1 minute
Clinton lead Trump by thirteen million votes in the popular vote. Express it in scientific notation

10. But, still, how many zeros or how many digits?
Depends!
Depends on how precise the measurement
Adding zeros does not add precision or accuracy
In fact it may be misstating the precision-a lie!
How many pennies? Not a problem! Seven?

11. But in Chemistry we cannot always be sure
Sometimes it more than a Kilogram, but how much more?
I can be sure that its over 45, but how far over?
Remember the balance was made in China!
That brings us to Significant Figures!

12. Significant Figures is a trick to save us having to think
Any non-zero digit is significant
It’s the zeros that have us confused
What does a zero mean?
All nonzero digits are significant
Interior zeros are significant
Trailing zeros after a decimal are significant

13. Some zeros only hold place they don’t define precision!
These zeros are not significant, they do not define precision!
Leading zeros are not significant
Trailing zeros at the end of a number before a decimal point are not significant

14. Some numbers are exact-and have unlimited significant figures
Direct counting of units =7 pennies
Defined quantities-definitions =a meter
Integral numbers in an
= 1/2

15. Rounding off is related to significant figures
How much does she weigh?
Depends on why you are asking
And it depends on how much she paid and how big the airplane is that she is flying on
How much does she weigh?

16. You have known and estimated data
To how many significant figures?
<5 round down
>5 round up
All are correct but a realistic value would be 150
For sure 14X
Pretty sure 148
Estimated

17. Scientific Notation allows correct significant figures
1 1x102
x 102
x 102
Learn how to use Scientific Notation

18. In problem solving always use the proper sig figs
For addition and subtraction the rule is you can’t add value to garbage or subtract value from garbage

19. In multiplication and division you are limited by the least precise value
Your answer can have no more significant figures than your least precise value

20. Skillbuilder 2.3 Reporting the Right Number of Digits
Skillbuilders
Skillbuilder 2.3 Reporting the Right Number of Digits
A thermometer is used to measure the temperature of a backyard hot tub, and the reading is shown in Figure 2.4. Write the temperature reading to the correct number of digits.
Skillbuilder 2.4 Determining the Number of Significant Figures in a Number
How many significant figures are in each number?
(a) 58.31
(b)
(c) 2.7 × 103
(d) 1 cm = 0.01 m
(e) 0.500
(f) 2100

21. Skillbuilders
Skillbuilder 2.6 Significant Figures in Addition and Subtraction
Perform the calculations to the correct number of significant figures.
(a)
+5.621
–1.8
(b)
– 0.56

22. Skillbuilders
Skillbuilder 2.5 Significant Figures in Multiplication and Division
Perform each calculation to the correct number of significant figures.
(a) x×0.512 x×1.301 x ÷ 3.4
(b) ×x ÷ 89.5