Do Now Activity

• Sit down quietly in your assigned seat and begin writing 3 to 4 sentences about what is an atom and how atoms relate to elements. (8 minutes to complete this)

• This should be written in your notebook for this class or loose leaf paper if you do not have a note book yet.

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2

ChemistryLuskin Academy

Mr. BerlinIntroduction to Chemistry

Measurements

Significant figures

The Atom

Atomic Number and Mass Number

Isotopes

Measurements

Measured Numbers and Significant Figures

Measured Numbers

When you use a measuring tool is used to determine a quantity such as your height or weight. These type of numbers are called simply measured numbers.

Reading a Meterstick

. l2. . . . I . . . . I3 . . . .I . . . . I4. . cm

First digit (known) = 2 2.?? cm

Second digit (known) = 0.7 2.7? cm

Third digit (estimated) between 0.05- 0.07

Length reported = 2.75 cm

or 2.76 cm

or 2.77 cm

Known + Estimated Digits

Known digits 2 and 7 are 100% certain

The third digit 6 is estimated (uncertain)

In the reported length, all three digits

(2.76 cm) are significant including the

estimated one

Learning Check

. l8. . . . I . . . . I9. . . .I . . . . I10. . cm

What is the length of the line?

1) 9.3 cm

2) 9.32 cm

3) 9.33 cm

How your answer compare with your neighbor’s

answer? Why or why not?

Solution

. l8. . . . I . . . . I9. . . .I . . . . I10. . cmEstimate to the hundreth’s place (0.01 cm)

2) 9.32 cm

3) 9.33 cm

The estimated digit may be slightly different.

Both readings are acceptable.

Learning Check

l5. . . . I . . . . I6. . . .I . . . . I7. . cm

What is the length of the line?

1) 6.0 cm

2) 6.09 cm

3) 6.60 cm

Solution

l5. . . . I . . . . I6. . . .I . . . . I7. . cm

Estimate to the hundreth’s place (0.01 cm). The reading is between 6.0 and 6.1. You may have estimated 6.07 cm as well.

2) 6.09 cm

Zero as a Measured Number

. l3. . . . I . . . . I4 . . . . I . . . . I5. . cm

What is the length of the line?

First digit 4.?? cm

Second digit 4.6? cm

Last (estimated) digit is 4.60 cm

(not to the left or right of .5)

Exact Numbers

Obtained when you count objects2 soccer balls

1 watch

4 pizzasObtained from a defined relationship

1 foot = 12 inches

1 meters = 100 cmNot obtained with measuring tools

Learning Check

A. Exact numbers are obtained by

1. measuring

2. counting3. definition

B. Measured numbers are obtained by

1. measuring

2. counting

3. definition

Solution

A. Exact numbers are obtained by

2. counting

3. definition

B. Measured numbers are obtained by

1. Using a measuring tool

Learning Check

Classify each of the following as an exact (1)

or a measured (2) number.

A.___Gold melts at 1064°C

B.___1 yard = 3 feet

C.___A red blood cell with diameter 6 x 10-4 cm

D.___There were 6 hats on the shelf

E.___A can of soda contains 355 mL of soda

Solution

Classify each of the following as an exact (1) or a measured(2) number. Give reason.

A. 2 Requires a thermometer(measuring tool)

B. 1 From a definition in U.S. system

C. 2 Need measuring tool to determine

D. 1 Counted the hats

E. 2 Measured

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Measurements

Significant Figures in Calculations

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Significant Figures in Measurement

The numbers reported in a measurement are limited by the measuring tool

Significant figures in a measurement include the known digits plus one estimated digit

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Counting Significant Figures

Number of Significant Figures

38.15 cm 4

5.6 ft 2

65.6 lb ___

122.55 m ___

Complete: All non-zero digits in a measured number are (significant or not significant).

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Leading Zeros

Number of Significant Figures

0.008 mm 1

0.0156 oz 3

0.0042 lb ____

0.000262 mL ____

Complete: Leading zeros in decimal numbers are

(significant or not significant).

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Sandwiched Zeros

Number of Significant Figures

50.8 mm 3

2001 min 4

0.702 lb ____

0.00405 m ____

Complete: Zeros between nonzero numbers are

(significant or not significant).

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Trailing Zeros

Number of Significant Figures

25,000 in. 2

200 yr 1

48,600 gal 3

25,005,000 g ____

Complete: Trailing zeros in numbers without decimals are (significant or not significant) if they are serving as place holders.

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Learning Check

A. Which answers contain 3 significant figures?1) 0.4760 2) 0.00476 3) 4760

B. All the zeros are significant in

1) 0.00307 2) 25.300 3) 2.050 x 103

C. 534,675 rounded to 3 significant figures is

1) 535 2) 535,000 3) 5.35 x 105

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Solution

A. Which answers contain 3 significant figures?2) 0.00476 3) 4760

B. All the zeros are significant in

2) 25.300 3) 2.050 x 103

C. 534,675 rounded to 3 significant figures is

2) 535,000 3) 5.35 x 105

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Learning Check

In which set(s) do both numbers contain the same number of significant figures?

1) 22.0 and 22.00

2) 400.0 and 40

3) 0.000015 and 150,000

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Solution

In which set(s) do both numbers contain the same number of significant figures?

3) 0.000015 and 150,000

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State the number of significant figures in each of the following:

A. 0.030 m 1 2 3

B. 4.050 L 2 3 4

C. 0.0008 g 1 2 4

D. 3.00 m 1 2 3

E. 2,080,000 bees 3 5 7

Learning Check SF3

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A. 0.030 m 2

B. 4.050 L 4

C. 0.00008 g 1

D. 3.00 m 3

E. 2,080,000 bees 3

Solution

Exit Question….

• Remain in your seats until the bell rings.

• “What are significant figures in your own words? How are zeros counted in regards to significant figures? What did you learn about measuring tools and how accurate they can be?”

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Do Now activity….Answer the following:

How many significant figures in; a) 0.00065 cm, b) 4.50 cm, c) 7600 feet, d) 3406.05 mm, e) 550 ml, f) 0.780 km

Which would be the proper tool to measure 4.5 ml of water; a) 100 ml graduated cylinder, b) 10 ml graduated cylinder, 10 ml beaker

For measuring a room in feet a) meter stick, b) tape measure, c) ruler 30

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Significant Numbers in Calculations

A calculated answer cannot be more precise than the measuring tool.

A calculated answer must match the least precise measurement.

Significant figures are needed for final answers from

1) adding or subtracting

2) multiplying or dividing

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Adding and Subtracting

The answer has the same number of decimal places as the measurement with the fewest decimal places.

25.2 one decimal place

+ 1.34 two decimal places

26.54

answer 26.5 one decimal place

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Learning Check

In each calculation, round the answer to the correct number of significant figures.

A. 235.05 + 19.6 + 2.1 =

1) 256.75 2) 256.8 3) 257

B. 58.925 - 18.2 =

1) 40.725 2) 40.73 3) 40.7

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Solution

A. 235.05 + 19.6 + 2.1 =

2) 256.8

B. 58.925 - 18.2 =

3) 40.7

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Multiplying and Dividing

Round (or add zeros) to the calculated answer until you have the same number of significant figures as the measurement with the fewest significant figures.

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Learning Check

A. 2.19 X 4.2 = 1) 9 2) 9.2 3) 9.198

B. 4.311 ÷ 0.07 = 1) 61.58 2) 62 3) 60

C. 2.54 X 0.0028 =

0.0105 X 0.060

1) 11.3 2) 11 3) 0.041

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Solution

A. 2.19 X 4.2 = 2) 9.2

B. 4.311 ÷ 0.07 = 3) 60

C. 2.54 X 0.0028 = 2) 11 0.0105 X 0.060

Continuous calculator operation =

2.54 x 0.0028 0.0105 0.060

Precision, accuracy and measurements

• https://www.youtube.com/v/b38hFWvEjwI

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Atomic Theory

Atoms are building blocks of elements. Remember how

tiny an atom is. Billions of atoms are on a pencil tip.

Similar (same) atoms in each element

Different from atoms of other elements

Two or more different atoms bond in simple ratios to

form compounds (Molecules)

40

Subatomic Particles: atoms are made of smaller particles.

Particle Symbol Charge RelativeMass

Electron e- 1- 0

Proton p+ + 1

Neutron n 0 1

41

Location of Subatomic Particles

Atom size about 10 -8 cm

Neutron (0)

Proton (+)

Electron (-)

Bohr Atomic Model

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Modern Atomic Model

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Atomic model overview

• https://www.youtube.com/v/UDIprICe9kg

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Atomic Number

Atomic number is the number of protons in an atom (the positive sub-atomic particle)

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Atomic Number - The periodic table is arranged by the atomic number.

11

Na

Atomic Number

Symbol

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All atoms of an element have the same number of protons

11

Na

11 protons

Sodium

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Periodic Table

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https://www.youtube.com/v/IsBZx0tv6dQ

• https://www.youtube.com/v/k6NlVM5YBsw

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Learning Check

State the number of protons for atoms of each of the following:

A. Nitrogen

1) 5 protons 2) 7 protons 3) 14 protons

B. Sulfur

1) 32 protons 2) 16 protons 3) 6 protons

C. Barium

1) 137 protons 2) 81 protons 3) 56 protons

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Solution

State the number of protons for atoms of each of the following:

A. Nitrogen

2) 7 protons

B. Sulfur

2) 16 protons

C. Barium

3) 56 protons

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Mass Number

Counts the number

of

protons and neutrons

in an atom

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Atomic Symbols

Show the mass number and atomic number

Give the symbol of the element

mass number

23 Na sodium-23

atomic number 11

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Number of Electrons

An atom is neutral on the Periodic TableThe net charge is zeroNumber of protons = Number of electronsAtomic number = Number of electrons

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Subatomic Particles in Some Atoms

16 31 65

O P Zn

8 15 30

8 p+ 15 p+ 30 p+

8 n 16 n 35 n8 e- 15 e- 30 e-

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Isotopes

Atoms with the same number of protons, but

different numbers of neutrons.

Atoms of the same element (same atomic

number) with different mass numbers

Isotopes of chlorine

35Cl 37Cl17 17

chlorine - 35 chlorine - 37

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Learning Check

Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.

12C 13C 14C 6 6 6

#p _______ _______ _______

#n _______ _______ _______

#e _______ _______ _______

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Solution

12C 13C 14C 6 6 6

#p 6 6 6

#n 6 7 8

#e 6 6 6

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Learning Check

An atom of zinc has a mass number of 65.

A. Number of protons in the zinc atom

1) 30 2) 35 3) 65

B. Number of neutrons in the zinc atom

1) 30 2) 35 3) 65

C. What is the mass number of a zinc isotope

with 37 neutrons?

1) 37 2) 65 3) 67

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Solution

An atom of zinc has a mass number of 65.

A. Number of protons in the zinc atom

1) 30

B. Number of neutrons in the zinc atom

2) 35

C. What is the mass number of a zinc isotope

with 37 neutrons?

3) 67

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Learning Check

Write the atomic symbols for atoms with the following:

A. 8 p+, 8 n, 8 e- ___________

B. 17p+, 20n, 17e- ___________

C. 47p+, 60 n, 47 e- ___________

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Solution

16OA. 8 p+, 8 n, 8 e- 8

B. 17p+, 20n, 17e- 37Cl 17

C. 47p+, 60 n, 47 e- 107Ag 47

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Atomic Mass on the Periodic Table

11

Na

22.99

Atomic Number

Symbol

Atomic Mass

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Atomic Mass

Atomic mass is the weighted average mass of all the atomic masses of the isotopes of that atom.

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Example of an Average Atomic Mass

Cl-35 is about 75.5 % and Cl-37 about 24.5% of natural chlorine.

35 x 75.5 = 26.4 100

35.5

37 x 24.5 = 9.07

100

Exit Question….

What is a proton? What is a neutron? What is an electron? What is atomic number? How is the periodic table arranged?

Once you are done remain in your seats and turn in your exit question as you leave the classroom.

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