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Atoms and Elements. The Atom Atomic Number and Mass Number Isotopes. The Atom. An atom is the smallest particle that retains the characteristics of an element. Atomic Theory. Atoms are building blocks of elements Similar atoms in each element Different from atoms of other elements - PowerPoint PPT Presentation
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LecturePLUS Timberlake 1
Atoms and Elements
The Atom
Atomic Number and Mass Number
Isotopes
LecturePLUS Timberlake 2
The Atom
An atom is the smallest particle that retains the
characteristics of an element
LecturePLUS Timberlake 4
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
The Parts of the AtomAtoms are composed
of three subatomic particles:
• Protons have a positive charge (+)
• Electrons carry a negative charge (-)
• Neutrons are electrically neutral.
LecturePLUS Timberlake 6
Subatomic Particles
Particle Symbol Charge RelativeMass
Electron e- 1- 0
Proton p+ + 1
Neutron n 0 1
LecturePLUS Timberlake 7
Location of Subatomic Particles
10-13 cm
electrons
protons
neutrons
10-8 cm
nucleus
The Structure of the Atom The protons and
neutrons, each with a mass of about 1 amu are found in the tiny, dense nucleus.
The electrons are located outside the nucleus.
Models of the Atom
9
LecturePLUS Timberlake 10
Atomic Number
Counts the number
of
protons
in an atom
LecturePLUS Timberlake 11
Atomic Number on the Periodic Table
11
Na
Atomic Number
Symbol
LecturePLUS Timberlake 12
All atoms of an element have the same number of protons
11
Na
11 protons
Sodium
LecturePLUS Timberlake 13
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
LecturePLUS Timberlake 14
Periodic Table
1 2 3 4 5 6 7 8
11 Na
LecturePLUS Timberlake 15
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 16
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 17
Number of Electrons
An atom is neutral The net charge is zeroNumber of protons = Number of electronsAtomic number = Number of electrons
LecturePLUS Timberlake 18
Mass Number
Counts the number
of
protons and neutrons
in an atom
LecturePLUS Timberlake 19
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 20
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 21
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 22
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 23
Solution
12C 13C 14C 6 6 6
#p 6 6 6
#n 6 7 8
#e 6 6 6
LecturePLUS Timberlake 24
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 25
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 26
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 27
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 28
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 29
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
LecturePLUS Timberlake 30
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.
LecturePLUS Timberlake 31
Atomic Mass on the Periodic Table
11
Na
22.99
Atomic Number
Symbol
Atomic Mass
LecturePLUS Timberlake 32
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 33
Atomic Mass
Atomic mass is the weighted average mass of all the atomic masses of all the isotopes of that atom.
Weighted Average
• You have two types of coins: pennies and quarters.The pennies have a mass of 5g.The quarters have a mass of 15g.57% of the coins are pennies, 43% of the coins are quarters.What is the average mass of your coins?
34
Weighted Average – Atomic Mass
• You have two isotopes of Boron: 10B and 11B.The 10B has a mass of 10amu.The 11B has a mass of 22 amu.57% of the atoms are 10B, 43% of the atoms are 11B.What is the average mass of your atoms?
35
LecturePLUS Timberlake 36
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
LecturePLUS Timberlake 37
Problem 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 38
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__
LecturePLUS Timberlake 39
Calculating Atomic Mass
Add :
Percent (%) abundance of each isotope
Multiplied by the
Mass of each isotope of that element
Weighted average = mass isotope1(%) + mass isotope2(%) + …
LecturePLUS Timberlake 40
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 41
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?
LecturePLUS Timberlake 42
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 43
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?
LecturePLUS Timberlake 44
Assign X and Y values:X = % 10B Y = % 11B
Determine Y in terms of X X + Y = 100
Y = 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
LecturePLUS Timberlake 45
Collect X terms
10.0 X - 11.0 X = 1080 - 1100
- 1.0 X = -20
-1.0 X = -20
-1.0 - 1.0
X = 20 % 10B
Y = 100 - X
% 11B = 100 - 20%
= 80% 11B
LecturePLUS Timberlake 46
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 47
Solution AT8
2) 70%Solution
X + Y = 100
Y = 100 - X
Solve for X:X (62.9) + (100 - X )(64.9) = 63.5
100 100
Multiply through by 100
62.9X + 6490 - 64.9X = 6350
-2.0 X = -140
X = 70%