Catalyst 9/19/12

• Welcome Back! This week all rules/procedures are now in place, which means you should all be wearing your IDS!

• In your notes, write down 3 class rules you remember from last week.

• Pick up your honors books!!! • BINDERS and FOLDER DUE TOMORROW!!!• Turnitin.com DUE FRIDAY (see website)• Class Dojo is in effect (participate!)

9/17-9/21 Week 2 HWASSIGNED DUE

Wed. 9/19 Book Problems: Ch2: Questions and Problems: 1, 5, 6, 8, 13abcefg. TURNITIN.COM DUE FRIDAY!

Signed Forms

Thurs. 9/20 Problem Set due next Monday! Binder, Book Problems, Turnitin.com

Fri. 9/21 Density Column Extra Credit, work on problem Set, Study for QUIZ Tuesday!

None

Mon. 9/24 Finish Density Blocks Lab, Study for Ch.2 Quiz tomorrow!

None

Tues. 9/25 Chris Jordan Turnitin.com Density Blocks Lab, Quiz TODAY

Scientific Notation, SI Units, and

Significant Figures

Scientific NotationWhy is scientific notation useful in science?

- Many measurements in science are very large or very small numbers. Scientific notation expresses these numbers as a product of a number between 1 and 10 and a power of ten.

1. Decimal placement…move the decimal point until you have a number between 1 and 10 623 6.23 x 10???

2. Exponent…how many times do you have to multiply the new number by 10 to

get the original number?623 = 6.23 x 10 x 10 = 6.23 x 102

Scientific Notation2. Exponent…multiplying by 10 is the same as moving the decimal point!

Think of scientific notation as a condensed representation of a number. The exponent tells you how many places and in which direction you need to move the decimal place to get the original number.

420000. = 4.2 x 105

0.000715 = 7.15 x 10-4

5 4 3 2 1

1 2 3 4

*REMEMBER LIP!Left Is Positive

Scientific Notation

Which one is the bigger number?A) 3,520B) 2.1 x 104

A) 0.065B) 9.8 x 10-5

B! 2.1 x 104 = 21,000

A! 9.8 x 10-5 = 0.000098

Scientific Notation

A few more examples…800 = 8 x 10 x 10

= 8 x 102

2531 = 2.531 x 10 x 10 x 10 = 2.531 x 103

0.0014 = 1.4 ÷ 10 ÷ 10 ÷ 10 = 1.4 x 10-3

Decimal after the first non-zero digit!

Scientific Notation Practice: Convert back to an ordinary number

1.87 x 10–5 =

3.7 x 108 =

7.88 x 101 =

2.164 x 10–2 =

0.0000187

370,000,000

78.8

0.02164

Convert to Scientific Notation:

12,340 =

0.369 =

0.008 =

1,000,000,000 =

1.234 x 104

3.69 x 10–1

8. x 10–3

1. x 109

No Cussing!The following 4-Letter

words are forbidden here:

Inch MileFoot PintYard Acre

And we never swear the BIG F (useoC)

Please keep it clean andMetric

SI System• The International System of Units• Derived Units Commonly Used in Chemistry

Map of the world where red represents countries which do not use the metric system

The International System of Units

• Lengthmeter m• Mass kilogram kg• Time second s• Amount of substance mole mol• Temperature Kelvin K• Electric current amperes amps• Luminous intensity candela cd

Quantity Name Symbol

Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 16

SI Unit PrefixesPrefix Symbol Meaning Power of 10mega- M 1,000,000 106

kilo- k 1,000 103

hecto- h 100 102

deca- da 10 101

----- ----- 1 100

deci- d 0.1 10-1

centi- c 0.01 10-2

milli- m 0.001 10-3

micro- 0.000001 10-6

nano- n 0.000000001 10-9

Significant figuresMethod used to express accuracy and

precision.

You can’t report numbers better than the method used to measure them.

67.20 cm = four significant figures

EstimatedDigit

Certain Digits

???

Significant figuresThe number of significant

digits is independent of the decimal point.

255 31.7 5.60 0.934

0.0150

These numbersAll have three

significant figures!

Significant figures

Zeros are what will give you a headache!

They are used/misused all of the time.

SEE p.24 in your book!

Rules for zerosLeading zeros are not significant.

Captive zeros are always significant!

0.421 - three significant figuresLeading zero

Trailing zeros are significant …IF there’s a decimal point!

114.20 - five significant figuresTrailing zero

???

???

4,008 - four significant figuresCaptive zeros

???

Examples

250 mg \__ 2 significant figures 120. miles \__ 3 significant figures 0.00230 kg \__ 3 significant figures 23,600.01 s \__ 7 significant figures

Significant figures:Rules for zeros

Scientific notation - can be used to clearly express significant figures.

A properly written number in scientific notation always has the proper number of significant figures.

0.00321 = 3.21 x 10-3

Three SignificantFigures

Significant figures and calculations An answer can’t have more

significant figures than the quantities used to produce it.Example

How fast did you run if youwent 1.0 km in 3.0 minutes?

speed = 1.0 km 3.0 min

= 0.33 km min

+-1

/x

02 3

4 5 67 8 9

.

CE

EE

log

ln

1/x

x2

cos tan

0.333333

Significant figures and calculationsMultiplication and division.Your answer should have the same number of sig figs as the quantity in the calculation with the smallest number of significant figures.

21.4 cm x 3.095768 cm = 66.2 cm2

135 km ÷ 2.0 hr = 68 km/hr

ONLY 3 SIG FIGS!

ONLY 2 SIG FIGS!

Significant figures and calculationsAddition and subtractionYour answer should have the same number of digits to the right of the decimal point as the number having the fewest to start with.

123.45987 g+ 234.11 g 357.57 g

805.4 g- 721.67912 g 83.7 g

Rounding off numbers

After calculations, you may need to round off.

If the first insignificant digit is 5 or more, you round up

If the first insignificant digit is 4 or less, you round down.

If a set of calculations gave you the following numbers and you knew each was supposed to have four significant figures then -

2.5795035 becomes 2.580

34.204221 becomes 34.20

Examples of rounding off

1st insignificant digit

5.

Rewrite each of the following as an ordinary number

a. 4.31 x 10-2

b. 9.54 x 103

c. 3.79 x 10-5

d. 7.19 x 102

a. 0.0431b. 9540c. 0.0000379d. 719

8.

What will the exponent for the power of 10 be when each of the following numbers is written in scientific notation?

a. 3981.2b. 0.0004521c. 453.9d. 0.994 x 102

a. 3b. -4c. 2d. 1

Catalyst 9/20/12

Take out your class materials:•1 Binder•5 Dividers (Class Notes, Daily Hwk, Handouts/Labs, Quizzes/Tests, Reference •2 pocket folder•Scientific Calculator

Take out your homework and stamp sheet! In your class notes section, answer the following questions:

1. Which is smaller, 1 x 10-7 or 1 x 10-3

2. Which is larger, 2.3 x 103 or 1.8 x 106