1. Numbers in Science Chemists deal with very large numbers 602000000000000000000000

2. 299800000 m/s 0.000000000000000000000001673

3. Scientific Notation Is a way of making these numbers easier to write.

4. To write these numbers in scientific notation, move the decimal so that it is expressed as: A number between 1 and 10 Times ten to a power

5. Practice problems 12300= 2.5 X 10 3 = 1.0 X 10 -6 = 2.05 X 10 -3 =

6. The importance of units Numbers are used in science for quantifying measurements. However, all numbers must be followed by a unit!! Naked numbers have no meaning in science!

7. Measurements in science Observations in science should be quantified whenever possible. For this reason, scientists must master the tools used for measuring and the units that are used to express them.

8. General rules for measurement All units will be metric. Memorize the units for: Length = meter (m) mass = gram (g) volume = liter (L)

9. Prefixes used with the basic units Kilo- Centi- Milli-

10. Practice 1 kg = g1 m = cm 1 km = m1 L = mL 1 cm = m1 cm = mm 1 mL = L

11. Significant figures (digits) Pay attention to the precision of your tools Record all of the numbers in a measurement that you are certain of, plus one more (an approximation) called “the uncertainty.” All of the measured numbers, plus the uncertain number are called significant figures.

12. Why are they important? 1. They communicate the precision of the measuring tools used by the chemist. 2. They determine how precise the answers to calculations (using the measuring tools) can be.

13. Precision of Tools? What do you mean?

14. Significant figures (digits) are 1. Non-zero integers 2. Captive zeros Ex: 1.008 3. Trailing zeros with a decimal point 100..100

15. Significant figures are not 1. Leading zeros 0.0025 2.Trailing zeros without a decimal point 1000 3.Exact numbers—they have an unlimited # of Sig. figs. a) counts: 3 apples b) formula numbers:  r 2 c) definition: 1 inch = 2.54 cm

16. Significant figures in calculations 1. Multiplication and division rules Answer will have the same number of sig. figs. as the measurements with the smallest number of sig. figs. Ex: What is the density of an object with a mass of 10.00 g and a volume of 3.3 ml?

17. 2. Addition or Subtraction Answer will have the same number of decimal places as the measurement with the least number of decimal places. Ex: 1.013 mm + 12.11 mm + 8.0 mm =

18. Do you and your calculator have a communication problem? Solve the problem below using your calculator. 3.0 x 10 5 = 1.5 x 10 2 * 2.0 x 10 3

19. Calculations (4 X 10 2 )(2X 10 3 )= (4X10 2 )/(2X 10 -4 )=