2. Section 2.1 Units and Measurements
Define SI base units for time, length, mass, and temperature.
Explain how adding a prefix changes a unit.
Compare the derived units for volume and density.
Chemists use an internationally recognized system of units to communicate their findings.
Section 2-1

3. Units
Système Internationale d'Unités (SI) is an internationally agreed upon system of measurements.
A base unit
is a defined unit in a system of measurement that is based on an object or event in the physical world, and is independent of other units.
Section 2-1

4. Units (cont.)
Section 2-1

5. Units (cont.)
Section 2-1

6. The SI base unit of temperature is the kelvin (K).
Units (cont.)
The SI base unit of temperature is the kelvin (K).
Zero kelvin is the point where there is virtually no particle motion or kinetic energy, also known as absolute zero.
Two other temperature scales are Celsius and Fahrenheit.
Section 2-1

7. Not all quantities can be measured with SI base units.
Derived Units
Not all quantities can be measured with SI base units.
A unit that is defined by a combination of base units is called a derived unit.
Section 2-1

8. Derived Units (cont.)
Volume is measured in cubic meters (m3), but this is very large. A more convenient measure is the liter, or one cubic decimeter (dm3).
Section 2-1

9. is a derived unit, g/cm3, the amount of mass per unit volume.
Derived Units (cont.)
Density
is a derived unit, g/cm3, the amount of mass per unit volume.
The density equation is density = mass/volume.
Section 2-1

10. A B C D Section 2.1 Assessment
Which of the following is a derived unit?
A. yard
B. second
C. liter
D. kilogram A B C D
Section 2-1

11. A B C D Section 2.1 Assessment
What is the relationship between mass and volume called?
A. density
B. space
C. matter
D. weight A B C D
Section 2-1

12. Section 2.2 Scientific Notation and Dimensional Analysis
Express numbers in scientific notation.
Apply rules for significant figures to express uncertainty in measured and calculated values. (page 50 – 54)
Scientists often express numbers in scientific notation and solve problems using dimensional analysis.
Section 2-2

13. Scientific Notation Scientific notation
can be used to express any number as a number between 1 and 10 (the coefficient) multiplied by 10 raised to a power (the exponent).
Count the number of places the decimal point must be moved to give a coefficient between 1 and 10.
Section 2-2

14. Scientific Notation (cont.)
The number of places moved equals the value of the exponent.
The exponent is positive when the decimal moves to the left
800 =
The exponent is negative when the decimal moves to the right. =
Section 2-2

15. Scientific Notation (cont.)
Addition and Subtraction
Exponents must be the same.
Rewrite values with the same exponent.
Add or subtract coefficients.
Example: x 10-8
x 10-4
Section 2-2

16. Scientific Notation (cont.)
Multiplication and Division
To multiply:
multiply the coefficients
then add the exponents
(2.3 x 103)(4.0 x 105)
To divide:
divide the coefficients
then subtract the exponents
6.7 x 102
1.3 x 103
Section 2-2

17. Homework: page 38 2 page 39 4 - 9 page 41 11, 12 page 42 13

18. A B C D Section 2.2 Assessment
Which of the following expresses 9,640,000 in the correct scientific notation?
A  104
B  105
C × 106
D  610 A B C D
Section 2-2

19. include all known digits plus one estimated digit.
Significant Figures
Significant figures
include all known digits plus one estimated digit.
Section 2-3

20. Significant Figures (cont.)
Rule 1: Any non-zero digit is significant.
329 g
3 significant digits
3.299 x 10-6
4 significant digits
Rule 2: Any zero stuck between other numbers is significant.
2002
4 sig figs
3.09 x 10
3 sig figs

21. Significant Figures (cont.)
Rule 3: Zeros to the left of all the other digits are NEVER significant
.00345
3 sig figs
4 sig figs
Section 2-3

22. Significant Figures (cont.)
Rule 4: Zeros to the right of all the other digits
a.) ARE significant if there is a decimal point
a decimal point TELLS us that the number is a measurement
3900.
21.00
b.) are NOT significant if there is no decimal point.
no decimal point means that the number is an estimate
3900
621000
Section 2-3

23. Calculators are not aware of significant figures.
Rounding Numbers
Calculators are not aware of significant figures.
Answers should not have more significant figures than the original data with the fewest figures, and should be rounded.
Section 2-3

24. Homework
page – 37
page , 39

25. Rounding Numbers (cont.) Rules for rounding
If the digit to the right of the last significant figure is less than 5, do not change the last significant figure.
4.564  4.56
 36.5
Rule 2:
If the digit to the right of the last significant figure is greater than 5, round up to the last significant figure.
 23.6
6.557  6.56
Section 2-3

26. Rounding Numbers (cont.)
Rule 3:
If the digits to the right of the last significant figure are a 5 followed by a nonzero digit, round up to the last significant figure.
 2.54
Rule 4:
If the digits to the right of the last significant figure are a 5 followed by a 0 or no other number at all, look at the last significant figure. If it is odd, round it up; if it is even, do not round up.
 2.54
 2.52

27. Rounding Numbers (cont.)
Addition and Subtraction
First do the calculation
Then round the answer to the same number of decimal places (places to the right of the decimal point) as the number in the calculation with the fewest decimal places.
Note that it is not necessary to count the number of significant digits when adding or subtracting.
Multiplication and Division
Round the answer to the same number of significant figures as the original measurement with the fewest significant figures.
Section 2-3

28. A B C D Section 2.3 Assessment
Determine the number of significant figures in the following: 8,200, 723.0, and 0.01.
A. 4, 4, and 3
B. 4, 3, and 3
C. 2, 3, and 1
D. 2, 4, and 1 A B C D
Section 2-3

29. A B C D Section 2.3 Assessment
A substance has an accepted density of 2.00 g/L. You measured the density as 1.80 g/L. What is the percent error?
A g/L
B. –0.20 g/L
C g/L
D g/L A B C D
Section 2-3

30. Homework
page – 37
page , 39
page – 44

31. Section 2.3 Uncertainty in Data
Define and compare accuracy and precision.
Describe the accuracy of experimental data using error and percent error.
Convert between units using dimensional analysis. (pages 44 – 46)
Measurements contain uncertainties that affect how a result is presented.
Section 2-3

32. Accuracy and Precision
refers to how close a measured value is to an accepted value.
Precision
refers to how close a series of measurements are to one another.
Section 2-3

33. Accuracy and Precision (cont.)
Error
is defined as the difference between an experimental value and an accepted value.
Section 2-3

34. Accuracy and Precision (cont.)
The error equation is error = experimental value – accepted value.
Percent error
expresses error as a percentage of the accepted value.
Section 2-3

35. is a ratio of equivalent values having different units.
Dimensional Analysis
Dimensional analysis
is a systematic approach to problem solving that uses conversion factors to move, or convert, from one unit to another.
A conversion factor
is a ratio of equivalent values having different units.
Section 2-2

36. Dimensional Analysis (cont.)
Writing conversion factors
Conversion factors are derived from equality relationships, such as 1 dozen eggs = 12 eggs.
Percentages can also be used as conversion factors. They relate the number of parts of one component to 100 total parts.
Section 2-2

37. Dimensional Analysis (cont.)
Using conversion factors
A conversion factor must cancel one unit and introduce a new one.
Section 2-2

38. Steps to Problem Solving
Write down the given amount. Don’t forget the units!
Multiply by a fraction.
Use the fraction as a conversion factor. Determine if the top or the bottom should be the same unit as the given so that it will cancel.
Put a unit on the opposite side that will be the new unit. If you don’t know a conversion between those units directly, use one that you do know that is a step toward the one you want at the end.
Insert the numbers on the conversion so that the top and the bottom amounts are EQUAL, but in different units.
Multiply and divide the units (Cancel).
If the units are not the ones you want for your answer, make more conversions until you reach that point.

40. Metric Prefixes Kilo- means 1000 of that unit
1 kilometer (km) = meters (m)
Centi- means 1/100 of that unit
1 meter (m) = 100 centimeters (cm)
1 dollar = 100 cents
Milli- means 1/1000 of that unit
1 Liter (L) = milliliters (mL)

41. A B C D Section 2.2 Assessment
What is a systematic approach to problem solving that converts from one unit to another?
A. conversion ratio
B. conversion factor
C. scientific notation
D. dimensional analysis A B C D
Section 2-2

42. do the following problems:
Page
Page , 20
Page , 22, 24 – 26, 28 – 30
Page