11
The Atom
Atomic Number and Mass Number
Isotopes
22
Atomic TheoryAtomic 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
33
Subatomic ParticlesSubatomic Particles
Particle Symbol Charge RelativeMass
Electron e- 1- 0
Proton p+ + 1
Neutron n 0 1
44
Location of Subatomic ParticlesLocation of Subatomic Particles
10-13 cm
electrons
protons
neutrons
10-8 cm
nucleus
55
Atomic NumberAtomic Number
Counts the number
of
protons
in an atom
66
Periodic TablePeriodic 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
77
Periodic TablePeriodic Table
1 2 3 4 5 6 7 8
11 Na
88
Atomic Number on the Periodic Atomic Number on the Periodic TableTable
11
Na
Atomic Number
Symbol
99
All atoms of an element have All atoms of an element have the same number of protonsthe same number of protons
11
Na
11 protons
Sodium
1010
Learning Check AT 1Learning 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
1111
Solution AT 1Solution 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
1212
Number of ElectronsNumber of Electrons
An atom is neutral The net charge is zeroNumber of protons = Number of electronsAtomic number = Number of electrons
1313
Mass NumberMass Number
Counts the number
of
protons and neutrons
in an atom
1414
Atomic SymbolsAtomic Symbols
Show the mass number and atomic number
Give the symbol of the element
mass number
23 Na sodium-23
atomic number 11
1515
More Atomic SymbolsMore Atomic Symbols
16 31 65
O P Zn 8 15 30
8 p+ 15 p+ 30 p+
8 n 16 n 35 n
8 e- 15 e- 30 e-
1616
IsotopesIsotopes
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
1717
Questions 2Questions 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 _______ _______ _______
1818
Solutions 2Solutions 2
12C 13C 14C 6 6 6
#P __6___ _ 6___ ___6___
#N __6___ _ _7___ ___8___
#E __6___ _ 6___ ___6___
1919
Questions 3Questions 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
2020
Solutions 3Solutions 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
2121
Questions 4Questions 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- ___________
2222
Solutions 4Solutions 4
16OA. 8 p+, 8 n, 8 e- 8
B. 17p+, 20n, 17e- 37Cl 17
C. 47p+, 60 n, 47 e- 107Ag 47
2323
Questions 5Questions 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
2424
Solutions 5Solutions 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
2525
Masses of AtomsMasses 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.
2626
Atomic MassAtomic 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
2727
Questions 6Questions 6
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 __________
2828
Solution AT6Solution 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__
2929
Calculating Atomic MassCalculating Atomic Mass
Percentage (%) abundance of isotopes
Mass of each isotope of that element
Weighted average =
mass isotope1(%) + mass isotope2(%) + …
100 100
3030
Atomic Mass of MagnesiumAtomic 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
3131
Questions 7Questions 7
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?
3232
Solutions 7Solutions 7
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
3333
Finding An Isotopic MassFinding 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?
3434
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
3535
Collect X terms
10.0 X - 11.0 X = 1080 - 1100
- 1.0 X = -20
X = -20 = 20 % 10B
- 1.0
Y = 100 - X
% 11B = 100 - 20% = 80% 11B
3636
Questions 8Questions 8
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%
3737
Solutions 8Solutions 8
2) 70%
Solution
62.9X + 6490 = 64.9X = 6350
-2.0 X = -140
X = 70%