1. Units of Measurement
All measurements must include the number and the unit
Ex: 4.5 m or 23g/mL
Use SI System- International System of Units which includes the metric system

2. SI Units Length= meter (m) Mass= kilogram (kg) Time= seconds (s)
Temperature= Kelvin (K) ***
Pressure= pascal (Pa)

3. Derivied units
Area= m2 or cm2
Volume= cm3
Density= g/cm3 or g/mL

4. Non SI Units we will use Volume= Liter (L) or mililiter mL
Temperature= Celsius (oC)
Pressure= atmosphere (atm) or
millimeters of mercury (mmHg)

5. Units we NEVER measure in !!!
Fahrenheit °F
Inches, yards, feet etc.
Ounces, pounds
Cups, teaspoons, etc.
PSI (pounds per square inch)

6. Metric Prefixes Tera- Trillion (T) ex: Giga- Billion (G) ex:
Mega- Million (M) ex:
Kilo- Thousand (k) ex:
Hecto- Hundred (h) ex:
Deca- Ten (da) ex:
Deci- tenth (d) ex:
Centi- hundredth (c) ex:
Milli- thousandth (m) ex:
Micro- millionth (µ) ex:
Nano- billionth (n) ex:
Pico-trillionth (p) ex:

7. Uncertainty in Measurements
When you take down a measurement, take down all the numbers an instrument gives you PLUS one uncertain number you estimate
Ex: grams, the measurement is accurate only to The last digit is not accurate
If you get an exact amount put a decimal behind the last digit.
Ex: g
Yes you can have hanging decimals & if your math teacher says other wise send them to see me 

8. Reading Scales:
Count the # of marks between numbers to calculate scale
I l l l l l l l l l l l l l l l °C
l l l l l l l l l l l g mL

9. Why are measurements uncertain?
Human Error
Instruments are not flawless.
Always involves some estimation
Digital- the last digit is estimated.
Scales- human estimation

10. Significant Figures and Scientific Notation

11. Rules for Significant Figures (aka sig figs)
If your # > 1 (w/o a decimal) then-
Count all whole # and zero’s inbetween
Ex: 1234=
105=
300=
2030=

12. Sig Fig Rules continued
If your # is < 1 then-
Count the first whole # and all the numbers after it (including zero’s)
Ex: = = = =

13. Last Sig Fig Rule If the #>1 with a decimal then- Count ALL the #s
Ex: = = =

14. Adding and Subtracting
Use the least number of decimal places
5.000 cm cm cm cm
9.352 cm cm
Your only as “strong” as the weakest” link

15. 5.00 cm 2 decimal places - 4.352 cm 3 decimal places
0.65 cm is the correct answer in sig figs

16. 430 mm * This one is tricky!
+ 23 mm
453 mm
Still have to use the least significant place holder
430 is only significant to the ten’s place
so the correct answer (in sig figs) is
450 mm, not 453 mm
Why? an answer can only be as precise as the least precise number used in the calculation

17. Multiplying and Dividing
multiply or divide the numbers
count the total number of sig figs in each number
your final answer should have no more sig figs than the lowest number of sig figs you started with

18. 6.7 cm
x cm
7.37 cm2
7.4 cm2 is the correct answer in sig figs

19. Scientific Notation
In chemistry we often use very large or very small numbers.
54, 000
We want to be able to show these numbers without all insignificant zeros, so we use scientific notation.

20. 1. Make the number less than ten 2. Count the number of places the
decimal moves = the exponent.
3. If the original number is less than
one the exponent is negative, if greater than one its positive
Ex: =
Ex: =