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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.
LecturePLUS Timberlake 1
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
Timberlake lecture plus 17
Measurements
Significant Figures in Calculations
Timberlake lecture plus 18
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
Timberlake lecture plus 19
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).
Timberlake lecture plus 20
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).
Timberlake lecture plus 21
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).
Timberlake lecture plus 22
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.
Timberlake lecture plus 23
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
Timberlake lecture plus 24
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
Timberlake lecture plus 25
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
Timberlake lecture plus 26
Solution
In which set(s) do both numbers contain the same number of significant figures?
3) 0.000015 and 150,000
Timberlake lecture plus 27
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
Timberlake lecture plus 28
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?”
LecturePLUS Timberlake 29
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
Timberlake lecture plus 31
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
Timberlake lecture plus 32
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
Timberlake lecture plus 33
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
Timberlake lecture plus 34
Solution
A. 235.05 + 19.6 + 2.1 =
2) 256.8
B. 58.925 - 18.2 =
3) 40.7
Timberlake lecture plus 35
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.
Timberlake lecture plus 36
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
Timberlake lecture plus 37
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
LecturePLUS Timberlake 38
39
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
LecturePLUS Timberlake 42
Modern Atomic Model
LecturePLUS Timberlake 43
Atomic model overview
• https://www.youtube.com/v/UDIprICe9kg
LecturePLUS Timberlake 44
LecturePLUS Timberlake 45
Atomic Number
Atomic number is the number of protons in an atom (the positive sub-atomic particle)
LecturePLUS Timberlake 46
Atomic Number - The periodic table is arranged by the atomic number.
11
Na
Atomic Number
Symbol
LecturePLUS Timberlake 47
All atoms of an element have the same number of protons
11
Na
11 protons
Sodium
LecturePLUS Timberlake 48
LecturePLUS Timberlake 49
Periodic Table
LecturePLUS Timberlake 50
https://www.youtube.com/v/IsBZx0tv6dQ
• https://www.youtube.com/v/k6NlVM5YBsw
LecturePLUS Timberlake 51
LecturePLUS Timberlake 52
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
LecturePLUS Timberlake 53
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
LecturePLUS Timberlake 54
Mass Number
Counts the number
of
protons and neutrons
in an atom
LecturePLUS Timberlake 55
Atomic Symbols
Show the mass number and atomic number
Give the symbol of the element
mass number
23 Na sodium-23
atomic number 11
LecturePLUS Timberlake 56
Number of Electrons
An atom is neutral on the Periodic TableThe net charge is zeroNumber of protons = Number of electronsAtomic number = Number of electrons
LecturePLUS Timberlake 57
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-
LecturePLUS Timberlake 58
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
LecturePLUS Timberlake 59
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 _______ _______ _______
LecturePLUS Timberlake 60
Solution
12C 13C 14C 6 6 6
#p 6 6 6
#n 6 7 8
#e 6 6 6
LecturePLUS Timberlake 61
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
LecturePLUS Timberlake 62
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
LecturePLUS Timberlake 63
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- ___________
LecturePLUS Timberlake 64
Solution
16OA. 8 p+, 8 n, 8 e- 8
B. 17p+, 20n, 17e- 37Cl 17
C. 47p+, 60 n, 47 e- 107Ag 47
LecturePLUS Timberlake 65
Atomic Mass on the Periodic Table
11
Na
22.99
Atomic Number
Symbol
Atomic Mass
LecturePLUS Timberlake 66
Atomic Mass
Atomic mass is the weighted average mass of all the atomic masses of the isotopes of that atom.
LecturePLUS Timberlake 67
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.
LecturePLUS Timberlake 68