Teaching the Metric System

Sally B. Mitchell sallybchemistry.com

For meaning and understanding

Identify the problem

Engineer a Solution to a problem with education

7 years of research

Writing to learn

Re-teach teachers (keep an open mind)

Numbers

How many ways can you express this number?

Three hundred million

Normal Notation

300,000,000

Scientific Notation

3 x 108

Engineering Notation

300 x 106

Metric Notation

300 M

Ways to express quantities

Written notation (three hundred million)

Number notation (300,000,000)

Scientific notation ( 3 x 108)

Engineering notation ( 300 x 106)

Metric notation ( 300 M)

Infinite number of other ways ( 30 x 107)

What is a metric prefix?

Quantity?

Number?

Symbol?

Why do we even use prefixes?

Easier to write

Easier to say

Easier to manipulate

It is concise

Do you know your prefixes?

10-12 10-9 10-6 10-3 100 103 106 109 1012

p n μ m k M G T

Try another0.000 000 000 032

Notice the spaces between groups of 3 numbers

3.2 x 10-11 (Scientific Notation)

32 x 10-12 (Engineering Notation)

32 p (Metric Notation)

What is the appropriate prefix for this quantity?

The time was 45,000,000,000 seconds

45 Gs

The distance between the objects was 0.000 050 m

50 μm

Why change the prefix?Yet, we assess the student’s ability to CONVERT

from kilometers to nanometers on the first day of class!

Convert 2 km to nm

REALLY? Is this a conversion?

Sound Mathematical Principles

2 x 103 m

Multiplicative Identity and Multiplicative Inverse

2 x 103 x ( ) m10-9109 x

Associative Law and

Law of Exponents

(2 x 103 x 109 ) x 10-9 m

2 x 1012 x 10-9 m

Substitution of Symbol

2 x 1012 nm

Check it

2 km = 2 x 1012 nm?

Look at only the quantity

2 k = 2 x 1012 n?

2 x 103 = 2 x 1012 x 10-9

Calculate the density of radon gas at STP

Mass = 450 mg Volume = 50 mL

Express your answer in g/L

Density = 9 g/L

100 % confidenceTeach about numbers and different ways to

express

Review Scientific Notation

Introduce Engineering Notation

Discuss prefixes

Remember to develop “Prefixes are symbols”

Challenge your students to express quantities using different symbols

Remember

NO DIMENSIONAL ANALYSIS

No tricks

No centi

Groups of 3 (300,000,000 0.000 000 000 032)

What is a MOLE?

6.02 x 1023 ?

602 x 1021 ?