The SI System of Measurement
The Nature of Measurement
A Measurement is a quantitative
observation consisting of TWO parts
Part 1 - number
Part 2 - scale (unit)
Examples:
20 grams
6.63 x 10-34 Joule·seconds
Derived SI Units
Combinations of SI base units form derived units.
pressure is measured in kg/m•s2, or pascals
SI Prefixes
Common to Chemistry
Prefix
Kilo
Deci
Centi
Milli
Micro
Unit Abbr.
k
d
c
m

Exponent
103
10-1
10-2
10-3
10-6
Metric Conversions
103
102
101
g
m
L
kilo hecto deka Base
unit
10-1
10-2
10-3
deci centi milli
Conversions in the metric system are
merely a matter of moving a decimal point.
The “base unit” means the you have a
quantity (grams, meters, Liters, etc without
a prefix.
Metric Conversions
103
102
101
g
m
L
kilo hecto deka Base
unit
18 L
10-1
10-2
10-3
deci centi milli
1
2
3
18 liters = 18 000 milliliters
Example #1: Convert 18 liters to milliliters
Metric Conversions
103
102
101
g
m
L
kilo hecto deka Base
unit
450 mg = 0.450 g
10-1
10-2
10-3
deci centi milli
3
2
1
450 mg
Example #2: Convert 450 milligrams to grams
Metric Conversions
103
102
101
g
m
L
10-1
10-2
10-3
kilo hecto deka Base deci centi milli
unit
2
3
1
4
5
6
20 kg
20 kg = 20 000 000 mg
Example #3: Convert 20 kilograms to milligrams
Conversion Factors
A conversion factor is a ratio derived from the equality
between two different units that can be used to
convert from one unit to the other.
example: How quarters and dollars are related
4 quarters
1
1 dollar
1 dollar
1
4 quarters
0.25 dollar
1
1 quarters
1 quarter
1
0.25 dollar
Conversion Factors, continued
Dimensional analysis is a mathematical technique
that allows you to use units to solve problems
involving measurements.
quantity sought = quantity given × conversion factor
example: the number of quarters in 12 dollars
number of quarters = 12 dollars × conversion factor
4 quarter
? quarters  12 dollars 
 48 quarters
1 dollar
Factor
Name
Symbol
Factor
Name
Symbol
1024
Yotta
Y
10-1
Deci
d
1021
Zetta
Z
10-2
Centi
c
1018
Exa
E
10-3
Milli
m
1015
Peta
P
10-6
Micro
μ
1012
Tera
T
10-9
Nano
n
109
Giga
G
10-12
Pico
p
106
Mega
M
10-15
Femto
f
103
Kilo
k
10-18
Atto
a
102
Hecto
h
10-21
Zepto
z
101
Deka
da
10-24
Yocto
y
Using Conversion Factors
Conversion Factors, continued
Sample Problem B
Express a mass of 5.712 grams in milligrams and
in kilograms.
Conversion Factors, continued
Sample Problem B Solution
Express a mass of 5.712 grams in milligrams and in
kilograms.
Given: 5.712 g
Unknown: mass in mg and kg
Solution: mg
1 g = 1000 mg
Possible conversion factors:
5.712 g 
1000 mg
1g
and
g
1000 mg
1000 mg
 5712 mg
g
Conversion Factors, continued
Sample Problem B Solution, continued
Express a mass of 5.712 grams in milligrams and in
kilograms.
Given: 5.712 g
Unknown: mass in mg and kg
Solution: kg
1 000 g = 1 kg
Possible conversion factors:
5.712 g 
1000 g
1 kg
and
kg
1000 g
1 kg
 0.005712 kg
1000 g