CHM 101

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CHM 101 Chapter Two

1. Daltons Atomic Theory
2. Discovery of atomic structure
3. Modern view of atomic theory
4. Atomic Weights
5. The Periodic Table
6. Molecules and Molecular Compounds
7. lons and ionic compounds
8. Naming inorganic compounds

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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.

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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 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 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 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 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.
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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.
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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
Protons
Neutons
Electrons
Name
53
74
53
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CHM 101 Average Atomic Mass

• The atomic mass unit is defined by assigning the
  mass of one atom of is exactly 12 amu.
  This leads to the relationship

• However, the mass of carbon in the Periodic
  Table is 12.01 amu

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CHM 101 Average Atomic Mass

• 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

• 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
50 63Cu 50 65Cu
25 63Cu 75 65Cu
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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 The Periodic Table
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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 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.

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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)

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CHM 101 Molecules and Molecular Compounds

• Compounds are represented by a variety of
  formulae that present different types of
  information

Sulfur trioxide
Dinitrogen tetraoxide
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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.

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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

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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
Name
Formula