jwallach

1. Units Introduction

2. All measurements need units
• If I said an object has a length of 10, would this make any sense?
• We need a unit with every number:
– Length = 10 inches
– Length = 10 feet
– Length = 10 meters
• Writing a number without a unit makes it meaningless

3. Standard Units
• In science, we like to use standard units so that everyone around the
world understands the measurements
• The following are the seven standard base units:
Measurement Unit Abbreviation
Length Meter m
Mass Kilogram kg
Time Second s
Amount of
Substance
Mole mol
Electric Current Ampere A
Luminous intensity Candela Cd
Temperature Kelvin K

4. Derived Units
• Notice how there are only 7 standard units. These are sufficient to cover
many more than 7 measurements when you combine the base units.
Below are a some examples of derived units – units that are combinations
of base units. There are many more than shown in the table.
Measurement Derived Unit Abbreviation In base
units
Area Square
meters
𝑚2
𝑚2
Energy Joule J 𝑘𝑔 ∙ 𝑚2
𝑠2
Pressure Pascal Pa 𝑘𝑔
𝑠2 ∙ 𝑚
Force Newton N 𝑘𝑔 ∙ 𝑚
𝑠2

5. Using Units in Chemistry
• While they are certainly required in chemistry, units can also be very
helpful. In calculations, if you are careful with your units, then it becomes
easy to spot mistakes in your calculations.
• As you go through the exercises in this and later units, you will see units
used quite a bit. Pay attention to them and ensure that when you are
doing calculations on your own that you incorporate units.
• For Blackboard, when entering numbers in as answers to problems, you
should not include units. The reason for this is that Blackboard can easily
misinterpret a unit. You should still have them on your own paper with
your calculation, just do not try to enter units in with the answers to the
problems.

6. Misconception Alert!
• Students like to use calculators instead of paper. They try to solve
questions on the calculator without taking the time to write the work out
on paper and show their units.
• Unless you are a student who is pretty certain you will get an A in the
course and can lay everything out in your head, you should have good
habits in solving problems. Get your problem set-up on paper before you
plug numbers into a calculator and ensure that your units are correct all
the way through the calculation.