Units Introduction

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

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

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

Energy Joule J

Pressure Pascal Pa

Force Newton N

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.

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.