Periodicity

1
Periodicity
2
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.

3
Classification of the Elements

• OBJECTIVES
• Use electron configurations to classify elements
  as noble gases, main group elements, transition
  metals, or inner transition metals.

4
Periodic Table Revisited

• Russian scientist Dmitri Mendeleev taught
  chemistry in terms of properties.
• Mid 1800s - molar masses of elements were known.
• Wrote down the elements in order of increasing
  mass.
• Found a pattern of repeating properties.

5
Mendeleevs Table

• 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.

6
The modern table

• Elements are still grouped by properties.
• Similar properties are in the same column.
• Order is by increasing atomic number.
• Added a column of elements Mendeleev didnt know
  about.
• The noble gases werent found because they didnt
  react with anything.

7

• Horizontal rows are called periods
• There are 7 periods

8

• Vertical columns called groups
• Elements are placed in columns by similar
  properties
• Also called families

9

• The elements in the A groups are called the
  representative elements
• outer s or p filling

8A0
1A
2A
3A
4A
5A
6A
7A
10

• The group B are called the transition elements

11

• Group 1A are the alkali metals
• Group 2A are the alkaline earth metals

12

• Group 7A is called the Halogens
• Group 8A are the noble gases

13
Why?

• 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
  repeats.
• The properties of atoms repeat.

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• 1s1
• 1s22s1
• 1s22s22p63s1
• 1s22s22p63s23p64s1
• 1s22s22p63s23p64s23d104p65s1
• 1s22s22p63s23p64s23d104p65s24d10 5p66s1
• 1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p67
  s1

15
He

• 1s2
• 1s22s22p6
• 1s22s22p63s23p6
• 1s22s22p63s23p64s23d104p6
• 1s22s22p63s23p64s23d104p65s24d105p6
• 1s22s22p63s23p64s23d104p65s24d10 5p66s24f145d106p6

2
Ne
10
Ar
18
Kr
36
Xe
54
Rn
86
16
S- block
s1
s2

• Alkali metals all end in s1
• Alkaline earth metals all end in s2
• really should include He, but it fits better
  later.
• He has the properties of the noble gases.

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Transition Metals -d block
s1 d5
s1 d10
d1
d2
d3
d5
d6
d7
d8
d10
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The P-block
p1
p2
p6
p3
p4
p5
19
F - block

• inner transition elements

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1 2 3 4 5 6 7

• Each row (or period) is the energy level for s
  and p orbitals.

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• d orbitals fill up after previous energy level,
  so first d is 3d even though its in row 4.

1 2 3 4 5 6 7
3d
22
1 2 3 4 5 6 7
4f 5f

• f orbitals start filling at 4f

23
Writing electron configurations the easy way
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Electron Configurations repeat

• The shape of the periodic table is a
  representation of this repetition.
• When we get to the end of the column the
  outermost energy level is full.
• This is the basis for our shorthand.

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The Shorthand

• Write symbol of the noble gas before the element,
  in .
• Then, the rest of the electrons.
• Aluminums full configuration
• 1s22s22p63s23p1
• previous noble gas Ne is 1s22s22p6
• so, Al is Ne 3s23p1

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More examples

• Ge 1s22s22p63s23p64s23d104p2
• Thus, Ge Ar 4s23d104p2
• Hf 1s22s22p63s23p64s23d104p65s2
  4d105p66s24f145d2
• Thus, Hf Xe6s24f145d2

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The Shorthand Again
Sn- 50 electrons
The noble gas before it is Kr
Takes care of 36
Next 5s2
Then 4d10
Finally 5p2
Kr
5s2
4d10
5p2