SI
UNITS
I. SI System
 In America, most people measure
things using the English or Imperial
System of Units.
 It is very confusing and has too many
units.
I. SI System
 Take length for an example:
 12 inches = 1 foot
 3 feet = 1 yard
 1760 yards = 1 mile
I. SI System
 Volume has gallons, quarts, pints, cups,
tablespoons, teaspoons, fluid ounces,
etc.
I. SI System
 In chemistry, we will use the
metric system.
 It is often called the International
System of Units, or in French,
Système International (SI).
 SI Units all have base units, and
then base all other measurements
on multiples of 10.
I. SI System
 THE METRIC SYSTEM IS EASY!
II. The Base Units
Quality
Length
Volume
Unit
meter
liter
or cubic
meter
Mass
kilogram
Temperature Kelvin,
Celcius
Time
second
Symbol
m
L
m3
(1 L = 1000
cm3)
kg
K, °C
s
Where do the Units Come From?
  The same place where everything good comes from…
  FRANCE!
III. The Definitions
  International Bureau for Weights and Measures in
Sèvres, France.
III. The Definitions
Kilogram - defined
as equal to the
mass of the
kilogram
prototype (the
piece of metal
shown sealed in
vacuum
chambers).
III. The Definitions
 The meter – the distance light travels in
1/299,792,458 of a second.
III. The Definitions
  Or…in other words…a little longer than a yard.
III. The Definitions
 The second – the
duration of
9,192,631,770
periods of a
certain radiation
emitted from
Cs-133.
III. The Definitions
 Gabriel Fahrenheit, 1714
III. The Definitions
  Forget Fahrenheit
  SI Units are °Celsius and Kelvin
  Endpoints:
0°C = freezing point of water
100°C = boiling point
III. The Definitions
 0 K = absolute zero
 No colder temp. b/c molecules stop
moving.
 Conversion factors:
 K = °C + 273.15
III. The Definitions
  Comparison…
IV. Density
 Density - amount of mass per unit of
volume.
 density = mass
or D = m
volume
0.86 g/cm3
19.3 g/cm3
V
DH2O = 1.0 g/cm3
Ex. #1
 Try this problem…
 A sample of aluminum metal has a
mass of 8.4 g. The volume of the
sample is 3.1 cm3. Calculate the density
of aluminum.