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CHM 101 – Chapter Two
1.
2.
3.
4.
5.
6.
7.
8.
Dalton’s Atomic Theory
Discovery of atomic structure
Modern view of atomic theory
Atomic Weights
The Periodic Table
Molecules and Molecular Compounds
lons and ionic compounds
Naming inorganic compounds
Department of Chemistry and Biochemistry
CHM 101 - Reeves
CHM 101 – Atomic Theory
Between 1803 and 1807, John Dalton proposed his Atomic
Theory to explain experimental observations about gases
and chemical reactions occurring in the gas phase.
• Each element is composed of extremely small particles called
atoms.
• All atoms of a given element are identical; atoms of different
elements are different and have different properties.
Department of Chemistry and Biochemistry
CHM 101 - Reeves
CHM 101 – Atomic Theory
Between 1803 and 1807, John Dalton proposed his Atomic
Theory to explain experimental observations about gases
and chemical reactions occurring in the gas phase.
•Atoms are not changed into different atoms; atoms are neither
created nor destroyed.
•Compounds are formed when atoms of at least two different
elements combine; a given compound always has the same
kind and ratio of atoms.
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CHM 101 - Reeves
CHM 101 – Experimental Evidence
In the late 19th and early 20th century, experimental evidence
began to accumulate that contradicted some of Dalton's basic ideas
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CHM 101 - Reeves
CHM 101 – Experimental Evidence
In the late 19th and early 20th century, experimental evidence
began to accumulate that contradicted some of Dalton's basic ideas
Department of Chemistry and Biochemistry
CHM 101 - Reeves
CHM 101 – Experimental Evidence
In the late 19th and early 20th century, experimental evidence
began to accumulate that contradicted some of Dalton's basic ideas
Department of Chemistry and Biochemistry
CHM 101 - Reeves
CHM 101 – Modern View of the Atom
The experiments of the early 20th century dispelled the
myth of the indestructible atom. Instead, we now believe
that the atom is itself composed of simpler particles. It is
convenient for chemists to focus on protons, neutrons
and electrons.
Department of Chemistry and Biochemistry
CHM 101 - Reeves
CHM 101 – Atomic Number & Mass
Atoms are identified by the atomic number (Z), which is the
number of protons ( ) in the nucleus. The atomic mass
is,approximately, the sum of the atom's protons and the
neutrons (
). For example, all Mg atoms have 12
protons.
Department of Chemistry and Biochemistry
CHM 101 - Reeves
CHM 101 – Atomic Number & Mass
Because atoms are electrically neutral, the number of
electrons = the number of proton. Ions are atoms that have
more (anions) or less (cations) electrons than protons.
Symbol
39
Protons Neutons Electrons
K
53
56
Name
Fe
74
53
3
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CHM 101 – Average Atomic Mass
• The atomic mass unit is defined by assigning the
12
mass of one atom of C is exactly 12 amu. This
leads to the relationship
1amu  1.66 x1024 g
• However, the mass of carbon in the Periodic
Table is 12.01 amu
6
C
12.01
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CHM 101 – Average Atomic Mass
6
C
12.01
Although carbon-12 is its most common isotope
(98.93%), carbon also contains 1.03% of the
isotope C-13, with an atomic mass of 13.00335
amu. Thus, the average atomic weight of
Carbon is:
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CHM 101 – Average Atomic Mass
29
Cu
63.564
Copper has two important isotopes, 63Cu and 65Cu.
Based on the atomic weight reported in the
Periodic Table, what are the approximate
abundances of the two isotopes?
90% 63Cu
10% 65Cu
75% 63Cu
25% 65Cu
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50% 63Cu
50% 65Cu
25% 63Cu
75% 65Cu
CHM 101 - Reeves
CHM 101 – The Periodic Table
When the elements are arranged in the order of
increasing atomic number, their properties are observed
to vary in a repeating or periodic pattern.
The Periodic Table arranges atoms in order of
increasing atomic number such that elements with
similar chemical and physical properties appear in the
same column (group) of the table.
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CHM 101 - Reeves
CHM 101 – The Periodic Table
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CHM 101 - Reeves
CHM 101
Molecules and Molecular Compounds
• Most atoms are metals at room temperature.
Metallic character increases as you go to the left
and down the Table. Nonmetals are concentrated
to the right and top of the Table. Metalloids are
between metals and nonmetals.
• Nonmetals combine together to form molecules by
sharing some of their valence electrons. Seven
nonmetal elements are most commonly found in
nature as diatomic molecules.
• When two or more different nonmetals combine, a
molecular compound is formed.
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CHM 101 - Reeves
CHM 101
Molecules and Molecular Compounds
Compounds are represented by a variety of formulae
that present different types of information:
• Space-filling model: represents the molecule's
actual spatial arrangement of atoms
• Structural formula: shows how atoms are
connected, using symbols to represent atoms.
Department of Chemistry and Biochemistry
CHM 101 - Reeves
CHM 101
Molecules and Molecular Compounds
• Molecular formula: provides number and symbol
for each atom in the compound
• Empirical formula: provides smallest whole-number
ratio of atoms in the compound.
• Binary molecular compounds are named using a
prefix before each atom to indicate how many there
are in the molecule. (cf pg 66 & Table 2.6)
Department of Chemistry and Biochemistry
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CHM 101
Molecules and Molecular Compounds
Compounds are represented by a variety of formulae
that present different types of information:
O
O S
O
O
O
N N
O
Space-Filling
Model
O
Structural
Formula
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SO3
SO3
Sulfur trioxide
N2O4
NO2
Dinitrogen
tetraoxide
Molecular
Formula
Empirical
Formula
Name
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CHM 101
Ions and Ionic Compounds
Positive ions (cations) form when atoms loose electrons.
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CHM 101
Ions and Ionic Compounds
• A-group metals form only one kind of cation, consistent with
their position in the Periodic Table. Cations have the same
name as the atoms from which they are derived.
Department of Chemistry and Biochemistry
CHM 101 - Reeves
CHM 101
Ions and Ionic Compounds
Cations form when atoms loose electrons.
• A-group metals form only one kind of cation, consistent with
their position in the Periodic Table. Cations have the same
name as the atoms from which they are derived.
• B-group (transition) metals can form two or more different
ions. To name them, a Roman Numeral following the
symbol is used to indicate the charge on the ion.
Cr3+:
Fe2+:
Ag+:
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CHM 101
Ions and Ionic Compounds
Negative ions (anions) form when atoms gain electrons.
Nonmetals consistently form anions.
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CHM 101
Ions and Ionic Compounds
A-group elements form only one kind of monatomic ion,
consistent with their position in the Periodic Table. They are
named by replacing the last syllable with "ide"
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CHM 101
Ions and Ionic Compounds
Anions may also be polyatomic, consisting of two or more
atoms covalently bonded together, with one or more extra
electrons.
• Some common polyatomic anions have names ending in
“ide”
• Oxyanions are polyatomic ions that contain one or more
oxygen atoms. Their names end in “ite” or “ate”.
• See rules on p. 62 regarding naming conventions.
Memorize common ions in Tables 2.4 & 2.5
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CHM 101
Ions and Ionic Compounds
• All stable materials are electrically neutral.
• Ionic compounds are formed through the attraction
of anions and cations and are named by combining
the cation and anion names
sodium chloride
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CHM 101
Ions and Ionic Compounds
To be electrically neutral, the ions are combined so
that the total positive charge = total negative charge
Cation
Anion
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Name
Formula
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