teaching the metric system sally b. mitchell sallybchemistry.com for meaning and understanding
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Teaching the Metric System
Sally B. Mitchell sallybchemistry.com
For meaning and understanding
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Identify the problem
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Engineer a Solution to a problem with education
7 years of research
Writing to learn
Re-teach teachers (keep an open mind)
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Numbers
How many ways can you express this number?
Three hundred million
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Normal Notation
300,000,000
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Scientific Notation
3 x 108
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Engineering Notation
300 x 106
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Metric Notation
300 M
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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)
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What is a metric prefix?
Quantity?
Number?
Symbol?
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Why do we even use prefixes?
Easier to write
Easier to say
Easier to manipulate
It is concise
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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
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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)
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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
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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?
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Sound Mathematical Principles
2 x 103 m
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Multiplicative Identity and Multiplicative Inverse
2 x 103 x ( ) m10-9109 x
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Associative Law and
Law of Exponents
(2 x 103 x 109 ) x 10-9 m
2 x 1012 x 10-9 m
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Substitution of Symbol
2 x 1012 nm
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Check it
2 km = 2 x 1012 nm?
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Look at only the quantity
2 k = 2 x 1012 n?
2 x 103 = 2 x 1012 x 10-9
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Calculate the density of radon gas at STP
Mass = 450 mg Volume = 50 mL
Express your answer in g/L
Density = 9 g/L
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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
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Remember
NO DIMENSIONAL ANALYSIS
No tricks
No centi
Groups of 3 (300,000,000 0.000 000 000 032)
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What is a MOLE?
6.02 x 1023 ?
602 x 1021 ?