Download Ch. 4 Atoms and Elements Early Atomic Theory

Ch. 4 Atoms and Elements
Chapter Overview
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Introduction to atomic theory [4.2, 4.3]
Properties of atomic particles, elements [4.4, 4.5]
Your friend, the Periodic Table! [4.6]
Atomic symbols [4.8]
Isotopes [4.8]
Average atomic mass [4.9]
Ions [4.7]
You are expected to know the names and symbols
for elements 1 - 20
(Hydrogen, H through Calcium, Ca)
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Early Atomic Theory
• Four elements from the
ancient Greeks: Air,
Earth, Fire and Water.
• Largely based in
astrology.
• Ideas present for how
these elements
combine to affect life!
http://www.c s.utk.edu/~mclennan/BA/AGEDE/Water.html
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Modern Atomic Theory (~1803 - 1930s)
Dalton’s Postulates
1. Each element is composed of tiny indestructable
particles, called atoms.
2. All atoms of a given element have the same
mass and other properties that distinguish them
from the atoms of other elements.
3. Atoms combine in simple, whole-number ratios
to form compounds.
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Modern Atomic Theory
• Through a series of experiments by Thompson,
Rutherford, and Millikan, the structure of an atom
and the characteristics of fundamental particles are
determined.
– Nucleus in center, surrounded by an electron cloud.
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Sub-Atomic Particles
Particle
Symbol
Charge (C)
Charge
Mass (kg)
Mass
(amu)
Electron
e-
-1.60218 x 10-19
-1
9.10939 x 10-31
0.00055
Proton
p, p+, H+
1.60218 x 10-19
+1
1.67262 x 10-27
1.0073
Neutron
N
0
0
1.67493 x 10-27
1.0087
1 p = 1 n = 1 amu; 1 e- = 1/1836 amu
1 amu = 1.66054 x 10-27 kg
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Properties of Atoms
• All atoms of the same element have identical
numbers of protons.
– All carbon atoms have 6 protons, all chromium
atoms have 24 protons.
• The mass of 1 p+ ≈ 1 n >> 1 e– The total number of p+ + n = mass of an atom
• Neutral atoms are charge neutral:
# p+ = # e – This is because protons and electrons have equal
and opposite charges! And opposites attract!
• Neutrons “dilute” the protons in the nucleus.
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Periodic Table Properties
• A Period: A horizontal row on the periodic table.
• A Family or Group: A vertical column on the periodic
table.
• Metals: conductors, malleable and ductile; mainly
solids at room temp.
• Metalloids: semiconductors; mainly solids at room
temp.
• Nonmetals: poor conductors; few solids, liquids,
mainly gases at room temp.
• Each time you step along the periodic table, you add
one proton and one electron to create a new element.
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Atomic Symbols
X = Element Symbol
A
Z
X
Z = Atomic Number
A = Mass Number
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Practice
Protons
Neutrons
A
31
39
B
32
38
C
38
50
D
31
38
Symbol
What is the relationship between A and D?
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More Practice
Name
Z
A
30
64
153
p+
n
e-
6
6
63
92
143
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Atomic masses
The masses on the periodic table do not match the
mass numbers!
Atomic Mass = a weighted average of the masses of
the isotopes.
Atomic Mass =
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! (relative abundance of isotope x exact mass of isotope)
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Atomic Masses
Example: What is the atomic mass of carbon?
12C: 98.89% abundance, 12.000 amu
13C: 1.11% abundance, 13.003354 amu
12
C: 0.9889 x 12.000 amu
13
C: 0.0111 x 13.003354 amu = 0.144 amu
mass = 12.01 amu
= 11.87 amu
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Problem
Iron(Fe):
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54Fe
5.845%
53.9396 amu
56 Fe
91.754%
55.9349 amu
57 Fe
2.119%
56.9354 amu
Determine the
average atomic
mass of iron.
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Problem
Iron(Fe):
54Fe
5.845%
53.9396 amu
56 Fe
91.754%
55.9349 amu
57 Fe
2.119%
56.9354 amu
Determine the
average atomic
mass of iron.
54
Fe: 0.05845 x 53.9396 amu = 3.153 amu
56
Fe: 0.91754 x 55.9349 amu = 51.323 amu
57
Fe: 0.02119 x 56.9354 amu = 1.206 amu
55.682 amu
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Problem
Lead(Pb):
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204Pb
1.48%
203.973 amu
206Pb
23.6%
205.975 amu
207Pb
22.6%
206.976 amu
208Pb
52.3%
207.977 amu
Determine the
average atomic
mass of lead.
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Ions
• Ions occur when there is an imbalance between
protons and electrons.
– Protons > electrons: the resulting ion is positive; this is
called a cation.
– Protons < electrons: the resulting ion is negative; this is
called an anion.
– Ion charge = # p+ - # e-
• Examples:
– A calcium ion has 20 p+ and 18 e-. The charge on the ion is
20 - 18 = +2 → Ca+2.
– A fluoride ion has 9 p+ and 10 e-. The charge on the ion is 9
- 10 = -1 → F- or F-1.
– How many electrons are in a phosphide ion, P-3?
-3 = 15 - # e# e- = 18 eCHEM 100 F07
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Predicting Ion Charges
We can use the Periodic Table to predict many
(but not all) ion charges.
Cations: Group # = charge
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Anions: 8 - (group #) = charge
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Predicting Ions
Determine the typical charge, the number of
protons and the number of electrons for the
following ions.
Element
Charge
# p+
# e-
Aluminum
Beryllium
Oxygen
Bromine
Potassium
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