Significant FiguresAgenda

•Review elements

•Notes on Significant Figures

•Practice

Alkali metals

Alkaline Earth Metals

Boron Family

Carbon Family

Nitrogen Family

Oxygen Family

Halogens

Quiz

Flip PT

New Elements

• Accuracy?

• Precision?

Formula for % composition?

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Significant Figures

Date:

Types of Numbers

• Counting – Numbers without units (whole numbers)– Ex: there are 6 chairs in the front row

• Measured– Numbers WITH units (actually measured)– Ex: 58.35 g

• Defined– Fractions or conversion factors– Ex: 12 inches = 1 foot, 2.54 cm = 1 inch

Determine the type of #Discuss with table partner

• 12 people

• 5.34 g

• 16 Tbsp in a cup

• 6 cans

• 16 oz in a pound

• 2.54 cm in an inch

• 40.75 in

• 2.25 cm

SF in numbers

• Counting – infinite, ∞

• Defined – infinite, ∞

• Measured – where the fun begins!

– Digits 1 – 9 ALWAYS count

Determine the # of SFDiscuss with table partner

• 12 people

• 5.34 g

• 16 Tbsp in a cup

• 6 cans

• 16 oz in a pound

• 2.54 cm in an inch

• 40.75 in

• 2.25 cm

SF for measured #

• Zeros SOMETIMES count– LEADING zeros NEVER COUNT

• 0234• 0.034

– MIDDLE zeros ALWAYS COUNT• 101• 5.001

2 SF

3 SF

3 SF

4 SF

SF for measured # CONT

– TRAILING zeros count if a decimal is present• 100.0• 0.900• 100

4 SF3 SF

1 SF

Determine type of ZERO, then # SFDiscuss with table partner

• 0.031 or 3.1*10-2cm

• 6.00 cm

• 107.05 cm

• 2.35*10-3g

• 12.05 mL

• 0.14 cm

• 3.01 cm

• 5.790 g

SF in Calculations

12.0 cm

+2.45 cm

14.45 cm

Round to tenth

14.5 cm

5.79 g

-3.2 g

2.59 g

Round to tenth

2.6 g

•Addition and subtraction-Round to least number of decimal places

SF in Calculations CONT

• Multiplication and division– Round to least number of SF

6 cm

*6 cm

36 cm2

Round to 1 SF

40 cm2

122.5 g/mL

2.0 mL

= 61.25 g

Round to 2 SF

61 g

Homework

• Complete SF worksheet

• Work on elements

– Quiz next Friday before Test

• Lab Report

– Rough Draft due Monday

– Final Draft due Wednesday

• Test next Friday