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1
Dalton’s Atomic Theory
1) Each element is composed of tiny,
individual particles called atoms.
2) Atoms are indivisible; they cannot be
created or destroyed.
3) All atoms of each element are
identical in every respect.
4) Atoms of one element are different
than atoms of other elements.
5) Atoms of different elements combine
to form compounds (whole # ratios).
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Fig. 5-1, p. 120
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Fig. 5-2, p. 121
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© 2009 Brooks/Cole - Cengage
Table 5-1, p. 122
ATOMIC COMPOSITION
• Protons
–
–
–
+ electrical charge
mass = 1.672623 x 10-24 g
relative mass = 1.007 atomic
mass units (u)
• Electrons
negative electrical charge
– relative mass = 0.0005 u
–
• Neutrons
no electrical charge
– mass = 1.009 u
–
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Fig. 5-CO, p. 119
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Fig. 5-3, p. 123
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Fig. 5-4, p. 123
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Nuclear Model of the Atom
• Atom has small, dense nucleus
• Nucleus contains all the positive
charge and most of the mass of atom
• Nucleus is surrounded by much larger
volume of nearly empty space that
makes up the rest of the atom (sizewise)
• This space contains the electrons; i.e.,
the negative charge to balance the
positive charge of the nucleus.
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ATOM
COMPOSITION
The atom is mostly
empty space
• protons and neutrons in
the nucleus.
PLAY MOVIE
• the number of electrons is equal to the
number of protons.
• electrons in space around the nucleus.
• extremely small. One teaspoon of water
has 3 times as many atoms as the Atlantic
Ocean has teaspoons of water.
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Atomic Number, Z
All atoms of the same element
have the same number of
protons in the nucleus, Z
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Al
26.981
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Atomic number, Z
Atom symbol
Atomic weight
Mass Number, A
• Mass Number (A)
= # protons + # neutrons
• A boron atom can have
A = 5 p + 5 n = 10 u
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A
10
Z
5
B
12
Isotopes
• Atoms of the same element (same Z)
but different mass number (A).
• Boron-10 has 5 p and 5 n: 105B
• Boron-11 has 5 p and 6 n: 115B
11B
10B
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Hydrogen Isotopes
Hydrogen has _____ isotopes
1 H
1
1 proton and 0
neutrons, protium
2 H
1
1 proton and 1
neutron, deuterium
3 H
1
1 proton and 2
neutrons, tritium
radioactive
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Isotope Composition
Isotope
Sulfur-32
Bromine79
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Electrons
Protons
Neutrons
Atomic Weight (Mass)
• This tells us the mass of one atom of
an element relative to one atom of
another element.
• Define one element as the standard
against which all others are measured
• Standard = carbon-12
C atom with 6 protons and 6 neutrons is
the mass standard
• = 12 atomic mass units (u)
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Det’n Atomic Mass
• Use “weighted” averages—includes
mass of each “naturally-occurring”
isotope X relative percentage of that
isotope.
• Can also tell which isotope is most
abundant by comparing to the atomic
mass in periodic table.
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11B
Isotopes
10B
• Because of the existence of isotopes, the
mass of a collection of atoms has an average
value. Average mass = ATOMIC WEIGHT
• Boron is 19.9% 10B and 80.1% 11B. That is, 11B
is 80.1 percent abundant on earth.
• i.e., for a sample of 100 atoms, ~20 would be
boron 10 and ~80 would be boron 11.
• For boron atomic weight
= 0.199 (10.0 u) + 0.801 (11.0 u) = 10.8 u
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Isotopes & Atomic Weight
• Because of the existence of isotopes, the
mass of a collection of atoms has an average
value.
• 6Li = 7.5% abundant and 7Li = 92.5%
– Atomic weight of Li = ______________
•
28Si
= 92.23%, 29Si = 4.67%, 30Si = 3.10%
– Atomic weight of Si = ______________
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Chlorine and Bromine
• Chlorine has 2 isotopes
• Chlorine 35 and chlorine 37
• Atomic mass (from periodic table) =
35.45
• Which isotope is most abundant?
• Bromine has 2 isotopes 79 and 81.
What can we say about their relative
abundance (based on the atomic
mass)?
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Table 5-2, p. 128
Masses of Isotopes
determined with a mass spectrometer
See Active Figure 2.3
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Periodic Table
• Dmitri Mendeleev (18341907) developed the modern
periodic table. Argued that
element properties are
periodic functions of their
atomic weights.
• We now know that element
properties are periodic
functions of their ATOMIC
NUMBERS.
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Table 5-3, p. 130
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Fig. 5-7, p. 131
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Fig. 5-8, p. 131
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Common Elements, p. 134
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Fig. 5-9, p. 134
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Regions of the Periodic Table
(Metalloids, Nonmetals are also “Main Group”)
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Fig. 11-23, p. 330
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Periods in the Periodic Table
(Horizontal Rows #1-7)
PLAY MOVIE
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Groups/Families in the
Periodic Table (Columns)
PLAY MOVIE
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Common Names of Groups
•
•
•
•
Group 1A
Group 2A
Group 7A
Group 8A
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Alkali Metals
Alkaline Earth Metals
Halogens
Noble Gases
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Fig. 11-19, p. 326
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Fig. 11-18, p. 325
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ELEMENTS THAT EXIST AS
MOLECULES
Allotropes of C
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ELEMENTS THAT EXIST AS
DIATOMIC MOLECULES
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ELEMENTS THAT EXIST AS
POLYATOMIC MOLECULES
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S8 sulfur
molecules
White P4 and polymeric
red phosphorus
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Table 5-4, p. 138
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Table 5-5, p. 139