or

Exploiting Electrons for Nefarious Reasons

by Dr. Deborah L. Boxall

PowerPoint can be used for data chunking….

What is the difference between accuracy and precision?

Good precisionLow accuracy

= average position

Low precisionHigh accuracy

Significant figures: represent the precision of a measurement

A 20 g weight is weighed on four different balances, and the four masses shown below were obtained. Which measurement is the most precise?

19.9 g 19.94 g 19.935 g 19.9351 g

19.9351 g is the most precise. It has the greatest number of significant figures.

# sig figs 3 4 5 6

Determining the number of significant figures:

1. All nonzero figures are significant.

2. The only time zeros are NOT significant is when they precede nonzero numbers.

#SigFigs?

1.15

101.5

0.015

Sci. Notation

0.00150

101.50

1.15 3

1.015 x 102 4

1.0150 x 102 5

1.5 x 10-2 2

1.50 x 10-3 3

Value

Math with significant figures:

Addition/subtraction: line up the decimal points. The answer is rounded to the same number of decimal places as the value with the least number of decimal places.

28.0 cm

23.542 cm

25.64 cm+

77.2 cm

(77.182 cm)

Rounding Rules:

1. Round up if the next number is greater than 5.

2. Round down if the next number is less than 5.

3. If the next number is exactly 5, round up only if the number to be rounded is ODD.

Ex: 1.15 and 1.25 both round to 1.2

Rounding Rules:

1. Round up if the next number is greater than 5.

2. Round down if the next number is less than 5.

3. If the next number is exactly 5, round up only if the number to be rounded is ODD.

Ex: 1.15 and 1.25 both round to 1.2

For example, add: 28.0 cm + 23.542 cm + 25.64 cmFor example, add: 28.0 cm + 23.542 cm + 25.64 cm

PowerPoint can also be used to demonstrate a problem-solving algorithm.

For example: after learning how to ‘read’ the periodic table to obtain oxidation numbers of the representative elements, the process of writing chemical formulas of simple binary compounds could be demonstrated.

Li: 1s2 2s1 Li+1: 1s2 3 p + 2 e = +1 charge

Atom Ion Oxidation number

Mg: 1s2 2s2 Mg+2: 1s2 4 p + 2 e = +2 charge

B: 1s2 2s2 2p1 B+3: 1s2 5 p + 2 e = +3 charge

C: 1s2 2s2 2p2 Carbon can either lose four electrons or gain four electrons and doesn’t form ions readily

N: 1s2 2s2 2p3 N-3: 1s2 2s2 2p6 7 p + 10 e = -3 charge

O: 1s2 2s2 2p4 O-2: 1s2 2s2 2p6 8 p + 10 e = -2 charge

F: 1s2 2s2 2p5 F-1: 1s2 2s2 2p6 9 p + 10 e = -1 charge

Oxidation Numbers of Representative Elements+1

+2 +3 -3 -2 -1± 4

Now, you try some…

Write the formulas for the combination of:

1. Sodium and chlorine

2. Boron and chlorine

3. Calcium and oxygen

4. Aluminum and fluorine

5. Boron and oxygen

6. Aluminum and oxygen

Na Cl+1 1-

B Cl+3 1-

Ca O+2 2-

Al F+3 1-

B+3 O 2-2

Al+3 O 2-2

PowerPoint can also be used to illustrate a dynamic concept.

For example, Collision Theory is used to explain why some reactions occur very slowly…

…while others occur very rapidly.

First premise: Reactants must collide in order to react and form products.

A2 + B2 2 AB

Collision Theory

Collision Theory

First premise: Reactants must collide in order to react and form products.

A2 + B2 2 AB

Second premise: Reactants must have the correct orientation to form the products upon collision

Collision Theory

First premise: Reactants must collide in order to react and form products.

A2 + B2 2 AB

Second premise: Reactants must have the correct orientation to form the products upon collision

Third premise: Reactants must have sufficient energy for the collision to result in formation of products

E < Ea

Collision Theory

First premise: Reactants must collide in order to react and form products.

A2 + B2 2 AB

Second premise: Reactants must have the correct orientation to form the products upon collision

Third premise: Reactants must have sufficient energy for the collision to result in formation of products

E > Ea

Reaction progress

En

erg

y

Ea

Activated complex: an unstable transition state between reactants and products. It can either fall back down on the reactant side or go on to the product side.

Hrxn

Reaction progress

En

erg

y

Ea

Hrxn

Ea

A catalyst speeds up the rate of a reaction by lowering the activation barrier

Reaction progress

En

erg

y

Hrxn

Ea

A catalyst speeds up the rate of a reaction by lowering the activation barrier

PowerPoint can also be used to tell a story.

In the following example, the fact-based story was intended to demonstrate that the scientific method is not some dusty old technique used only by dead guys that lived long ago…

Or limited to the socially inept stereotype associated with modern day scientists.

As a matter of fact…

Real people do science!

During WWII, Allied forces established a number of air bases on islands in the South Pacific. The influx of material goods improved the living conditions of the native islanders.

Airplanes bring good things to

the island.

The airplanes didn’t appear until after the man started

sitting in the metal shack.

The airplanes disappeared after

the man left.

Step 1: Make observationsI’ll apply the Scientific Method!

Airplanes bring good things to

the island.

The airplanes didn’t appear until after the man started

sitting in the metal shack.

The airplanes disappeared after

the man left.

Step 1: Make observations

If we put a man back in the metal

shack, the airplanes will come back.

Step 2: Formulate a hypothesis

If we put a man back in the metal

shack, the airplanes will come back.

Step 2: Formulate a hypothesisStep 3: Design an experiment

The man needs a table to work

at

and he needs to be wearing coverings

over his earsand a chair to

sit on

Step 3: Design an experiment

The man needs a table to work

at

and he needs to be wearing coverings

over his earsand a chair to

sit on

Step 4: Collect data

I wonder how long it will be before the

planes come back?

Thirty days later…

This isn’t working.

I need to change my approach.

Step 5: Revise hypothesis

Writing Assignment #1 (due tomorrow)

Write at least one paragraph describing a situation in which you applied, or attempted to apply the scientific method to solve a problem in your everyday life. Be sure to explicitly state your hypothesis, the results of your experiment (the data collected) and any conclusions that you were able to draw from the data.

And finally, answer the question:

What would you do differently if you were to do it all over again?

Different learning modalities can be accessed by incorporating sounds as well as visual effects into a PowerPoint animation.

Wave speed: How fast the wave is traveling through the medium

It’s possible to estimate how far away lightning has struck by counting the number of seconds between the flash and the arrival of the thunder.

It takes about 5 s for the sound of the thunder to travel one mile

Wave speed = 1 mile/5 s = 1700 m/5 s = 340 m/s

The speed of sound in air is about 340 m/s

In which direction was the xylophone played?

Frequency and Pitch

The shorter the bar, the higher the pitch.

• Shorter bar = shorter wavelength = higher frequency

• The higher the frequency, the higher the pitch

Doppler Effect: a change in pitch due to motion of the source of the wave or of the observer.

Source moving toward observer.Sound wave compressed

= higher frequency

Source moving away.Sound wave expanded

= lower frequency

Siren emits at a constant 300 Hz

Which way is the sound travelling?Toward the observer or away?

Away Toward

Diffraction: the bending of waves around an object

Diffraction around an obstacle

Diffraction through an opening

Diffraction around a corner

The amount of diffraction that occurs depends upon the size of the obstacle or opening and the wavelength of the incident wave

Links to websites with pedagogically useful material can be easily inserted into PowerPoint presentations.

All excerpted PowerPoint presentations were prepared over the course of the 2006-2007 school year using public domain materials…

…by a moderately OCD teacher, a cranky SRHS laptop, an even crankier IBM desktop computer, and PowerPoint 2003.