Chapter 5
Chemical Periodicity
Classification of the Elements
OBJECTIVES:
Explain why you can infer the
properties of an element based on
those of other elements in the
periodic table.
� Use electron configurations to
classify elements as noble gases,
representative elements, transition
metals, or inner transition metals.
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Mendeleev’s Table
Periodic Table Revisited
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Russian scientist Dmitri Mendeleev
taught chemistry in terms of
properties.
Mid 1800’s - molar masses of
elements were known.
Wrote down the elements in order of
increasing mass.
Found a pattern of repeating
properties.
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Mendeleev's Periodic Table
(1871)
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The Modern Periodic Table
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Grouped elements in columns by similar
properties in order of increasing atomic
mass.
Found some inconsistencies - felt that
the properties were more important than
the mass, so switched order.
Also found some gaps.
Must be undiscovered elements.
Predicted their properties before they
were found.
Elements are still grouped by properties.
Similar properties are in the same
column.
In 1913, Moseley changed the order to
increasing atomic number.
This added a column of elements
Mendeleev didn’t know about.
The noble gases weren’t found because
they didn’t react with anything.
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Horizontal rows are called Periods
There are 7 periods
Vertical columns called groups
Elements are placed in columns by
similar properties
Also called families
1
2
3
4
5
6
7
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1A
2A
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The elements in the A groups are
called the REPRESENTATIVE 8A
0
elements
3A 4A 5A 6A 7A
outer s or p filling
The group B are called the
transition elements
These are called the inner
transition elements, and they
belong here
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Group 1A are the alkali metals
Group 2A are the alkaline earth metals
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Group 7A is called the Halogens
Group 8A are the Noble Gases
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Why is the Periodic Table arranged
in Groups and Periods?
H
Li
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The part of the atom another atom sees
is the electron cloud.
More importantly the outside orbitals.
The orbitals fill up in a regular pattern.
The outside orbital electron
configuration, or VALENCE electron
configuration, repeats.
The properties of atoms repeat.
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1s22s1
1s22s22p63s1
• 1 Valence Electron
• s1 configuration
• Become +1 ions to
obtain the OCTET of
electrons
K
19
1s22s22p63s23p64s1
Rb
37
Cs
55
1s22s22p63s23p64s23d104p65s1
Fr
87
1s22s22p63s23p64s23d104p65s24d105p66s24
f145d106p67s1
1s22s22p63s23p64s23d104p65s24d10 5p66s1
• 7 Valence Electrons
• s2p5 configuration
• Become -1 ions to achieve
their octet of electrons
1s22s22p63s23p64s23d104p65s24d10
1s22s22p5
9F
1s22s22p63s23p5 17Cl
1s22s22p63s23p64s23d104p5
35Br
1s22s22p63s23p64s23d104p65s24d105p5
53I
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p5
85At
1s22s22p63s23p64s23d104p65s2
5p66s2
88Ra:
Group 1A Alkali metals
Group 7A Halogens
• 2 Valence Electrons
• s2 configuration
• Become +2 ions to
2
2
6
2
12Mg: 1s 2s 2p 3s
obtain OCTET of
22s22p63s23p64s2
electrons
Ca:
1s
20
2 2
4Be: 1s 2s
56Ba:
3
Na
11
1s1
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Group 2A Alkaline Earth Metals
38Sr:
1
1s22s22p63s23p64s23d104p65s24d105p6
6s24f145d106p67s2
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Group 8A Noble Gases
• 8 Valence Electrons
• s2p6 configuration
• Not reactive, have their
octet of electrons
1s2 He 2
1s22s22p6
Ne
10
Can we determine an element
simply from the Valence Electron
Configuration?
1s22s22p63s23p6 Ar18
Let’s try it …
1s22s22p63s23p64s23d104p6 Kr
1. 3s2
Mg
2. 5s25p4 Te
3. 4s23d6 Fe
36
1s22s22p63s23p64s23d104p65s24d105p6 Xe
54
1s22s22p63s23p64s23d104p65s24d10 Rn
5p66s24f145d106p6 86
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Lewis Dot Structures
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Lewis Dot structures are helpful in
visualizing bonding between atoms.
Dots correspond to the number of
valence electrons. These are the
electrons that are involved in
interactions between atoms.
Dots are placed around the element’s
symbol, 1 at a time, until pairing is
necessary.
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Lewis Dot Structures
K
Ca
In
C
P
S
F
The number of unpaired
dots corresponds to
the number of bonds
that the atom can
form in a compound.
What about ions?
02Br-
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Lewis Dot Structures
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