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Periodic Table: Patterns

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Title: Periodic Table: Patterns


1
Periodic Table Patterns
2
John Newlands
  • 1864
  • arranged elements in octaves
  • worked for some elements, but not all

3
Dimitri Mendeleev
  • Julius Lothar Meyer
  • both independently created a form of the periodic
    table

4
Dimitri Mendeleev
  • Mendeleev usually credited because he showed how
    useful the table could be to predict properties

5
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6
Using the periodic table
  • The periodic table has so much information
    contained in its organization that it will become
    your most valuable resource!!!

7
Periodic Law
  • Elements are arranged by atomic number, there is
    a periodic repetition in their physical and
    chemical properties.

8
Periodic Table
  • Horizontal rows
  • Called periods
  • 7 periods
  • Show the number of the shell

9
Periodic Table
  • Vertical columns
  • Called groups
  • Show the valance electrons
  • Elements in a group have similar physical and
    chemical properties

10
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11
Periodic Trends
  • We have already learned one periodic trend-
  • the way electrons are organized in atoms

12
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13
Some exceptions
  • Draw the electron configuration of
  • Cr
  • Cu

14
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15
Single electron
  • The energy of a single electron reflects how
    tightly bound that e- is to the nucleus (more
    negative energy)

16
Effective Charge
  • We assume that the electrons are bound by a
    positive charge Z
  • But there is an effective charge that e- feels

17
Effective Charge
  • The effective charge (Zeff) represents the net
    effect of the attraction of the nuclear charge
    and the repulsion of the other e-s

18
Effective Charge
  • An electron closer to the nucleus would feel more
    of the positive charge

19
Shielding
  • The protection by the inner electrons so that
    the outer electrons do not feel the full nuclear
    charge

20
Orbital Filling
  • Shielding helps explain why the orbitals are
    filled in the order that they are
  • The lower energy orbitals (ones closer to the
    nucleus) are always filled first

21
Orbital Shielding
  • Orbitals to the inside of the other orbitals do a
    good job of shielding the outer electrons

22
Polyelectronic Model
  • The energy required to remove an electron from an
    atom depends on two factors

23
Two Factors
  • The effective nuclear charge
  • The average distance of the electron from the
    nucleus

24
Atomic radius Half the distance between the
nuclei of two atoms. (Atoms are the same and
bonded together)
25
Element Characteristics
Radius size increases
Radius size decreases
26
Element Characteristics
  • Ionization energy
  • Energy required to remove an electron from an
    atom
  • Easier to remove an electron from group 1 than
    group 8
  • Easier to remove electrons that are farther away
    from the nucleus (elements at the bottom of a
    group)

Ionization energy generally decreases
Ionization energy increases
27
The general trend
  • As we go across a period from left to right, the
    first ionization energy increases

28
Why??
  • Electrons added in the same principle quantum
    level do not completely shield the increasing
    nuclear charge

29
Exceptions
  • Decreases in ionization energy moving across
    (i.e. N to O) is because e- in 2s provide some
    shielding for the 2p

30
Electron Affinity
  • The energy change associated with the addition of
    an electron to a gaseous atom
  • X(g) e- --gt X-(g)

31
Sign for the energy
  • Defined as energy change when electron is added
  • if addition is exothermic then the sign is
    negative

32
Electron affinity
  • What is the trend going down a group?
  • Generally becomes more positive b/c e- added at
    increasing distance

33
Trends...
  • Electron affinities generally become more
    negative from left to right across a period,
    there are several exceptions

34
Element Characteristics
  • Electronegativity
  • It is a measure of the element's ability to
    attract the electrons which are in a bond

Electronegativity decreases
Electronegativity increases
35
Element Characteristics
More nonmetallic
Liquids
Periodic Table
More metallic
Solids
36
Periodic Table Trends Summary
Atomic radius decreases
Ionization energy and Electronegativity increase
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