atomic mass
TRANSCRIPT
LecturePLUS Timberlake 1
The Atom
Atomic Number and Mass Number
Isotopes
LecturePLUS Timberlake 2
Atomic Theory
Atoms are building blocks of elements
Similar atoms in each element
Different from atoms of other elements
Two or more different atoms bond in simple
ratios to form compounds
LecturePLUS Timberlake 3
Subatomic Particles
Particle Symbol Charge RelativeMass
Electron e- 1- 0
Proton p+ + 1
Neutron n 0 1
LecturePLUS Timberlake 4
Location of Subatomic Particles
10-13 cm
electrons
protons
neutrons
10-8 cm
nucleus
LecturePLUS Timberlake 5
Atomic Number
Counts the number
of
protons
in an atom
LecturePLUS Timberlake 6
Periodic Table
Represents physical and chemical
behavior of elements
Arranges elements by increasing atomic
number
Repeats similar properties in columns
known as chemical families or groups
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Periodic Table
1 2 3 4 5 6 7 8
11 Na
LecturePLUS Timberlake 8
Atomic Number on the Periodic Table
11
Na
Atomic Number
Symbol
LecturePLUS Timberlake 9
All atoms of an element have the same number of protons
11
Na
11 protons
Sodium
LecturePLUS Timberlake 10
Learning Check AT 1
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 11
Solution AT 1
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 12
Number of Electrons
An atom is neutral The net charge is zeroNumber of protons = Number of electronsAtomic number = Number of electrons
LecturePLUS Timberlake 13
Mass Number
Counts the number
of
protons and neutrons
in an atom
LecturePLUS Timberlake 14
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 15
More Atomic Symbols
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 16
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 17
Learning Check AT 2
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 18
Solution AT 2
12C 13C 14C 6 6 6
#P __6___ _ 6___ ___6___
#N __6___ _ _7___ ___8___
#E __6___ _ 6___ ___6___
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Learning Check AT 3
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 20
Solution AT 3
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 21
Learning Check AT 4
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 AT 4
16OA. 8 p+, 8 n, 8 e- 8
B. 17p+, 20n, 17e- 37Cl 17
C. 47p+, 60 n, 47 e- 107Ag 47
LecturePLUS Timberlake 23
Learning Check AT 5
An atom has 14 protons and 20 neutrons.A. Its atomic number is
1) 14 2) 16 3) 34
B. Its mass number is1) 14 2) 16 3) 34
C. The element is1) Si 2) Ca 3) Se
D. Another isotope of this element is
1) 34X 2) 34X 3) 36X 16 14 14
LecturePLUS Timberlake 24
Solution AT 5
An atom has 14 protons and 20 neutrons.A. It has atomic number
1) 14
B. It has a mass number of3) 34
C. The element is1) Si
D. Another isotope of this element would be
3) 36X 14
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Masses of Atoms
A scale designed for atoms gives their small
atomic masses in atomic mass units (amu)
An atom of 12C was assigned an exact mass of
12.00 amu
Relative masses of all other atoms was
determined by comparing each to the mass of 12C
An atom twice as heavy has a mass of 24.00
amu. An atom half as heavy is 6.00 amu.
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Atomic Mass
Listed on the periodic table
Gives the mass of “average” atom of each
element compared to 12C
Average atom based on all the isotopes and their
abundance %
Atomic mass is not a whole number
Na22.99
LecturePLUS Timberlake 27
Learning Check AT6
Using the periodic table, specify the atomic mass of each element (round to the tenths place):
A. calcium __________
B. aluminum __________
C. lead __________
D. barium __________
E. iron __________
LecturePLUS Timberlake 28
Solution AT6
Using the periodic table, specify the atomic mass of each element (round to the tenths place):
A. calcium _40.1 amu _
B. aluminum _27.0 amu _
C. lead _207.2 amu_
D. barium _137.3 amu_
E. iron _55.8 amu__
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Calculating Atomic Mass
Percent(%) abundance of isotopes
Mass of each isotope of that element
Weighted average =
mass isotope1(%) + mass isotope2(%) + …
100 100
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Atomic Mass of Magnesium
Isotopes Mass of Isotope Abundance 24Mg = 24.0 amu 78.70%
25Mg = 25.0 amu 10.13%
26Mg = 26.0 amu 11.17%
Atomic mass (average mass) Mg = 24.3 amu
Mg24.3
LecturePLUS Timberlake 31
Learning Check AT7
Gallium is a metallic element found in
small lasers used in compact disc players.
In a sample of gallium, there is 60.2% of
gallium-69 (68.9 amu) atoms and 39.8% of
gallium-71 (70.9 amu) atoms. What is the
atomic mass of gallium?
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Solution AT7
Ga-69
68.9 amu x 60.2 = 41.5 amu for 69Ga
100
Ga-71 (%/100)
70.9 amu x 39.8 = 28.2 amu for 71Ga
100
Atomic mass Ga = 69.7 amu
LecturePLUS Timberlake 33
Finding An Isotopic Mass
A sample of boron consists of 10B (mass 10.0 amu) and 11B (mass 11.0 amu). If the average atomic mass of B is 10.8 amu, what is the % abundance of each boron isotope?
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Assign X and Y values:X = % 10B Y = % 11B
Determine Y in terms of XX + Y = 100Y = 100 - X
Solve for X:X (10.0) + (100 - X )(11.0) = 10.8
100 100
Multiply through by 10010.0 X + 1100 - 11.0X = 1080
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Collect X terms 10.0 X - 11.0 X = 1080 - 1100
- 1.0 X = -20
X = -20 = 20 % 10B - 1.0Y = 100 - X
% 11B = 100 - 20% = 80% 11B
LecturePLUS Timberlake 36
Learning Check AT8
Copper has two isotopes 63Cu (62.9 amu) and 65Cu (64.9 amu). What is the % abundance of each isotope? (Hint: Check periodic table for atomic mass)
1) 30% 2) 70% 3) 100%
LecturePLUS Timberlake 37
Solution AT8
2) 70%
Solution
62.9X + 6490 = 64.9X = 6350
-2.0 X = -140
X = 70%