Electron configuration and Periodic Properties.

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Section 5-3

• Electron configuration and Periodic Properties.

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Information Contained in the Periodic Table

• Grps. of Representative elements exhibit similar
  chemical properties that change in a regular way.
• Each group has the same valence electron
  configuration.

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The number and type of valence electrons,
primarily, determine an atoms chemistry.
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Special Names for Groups in the Periodic Table
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Atomic Radius

• Just as size of orbital cant be exactly
  specified,
• Size of an atom cant be exactly specified.
• 1) Covalent Atomic radii
• 2) Metallic Radii

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Figure 7.34The Radius of an Atom
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Figure 7.35Atomic Radii for Selected Atoms
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• Ion An atom or group of atoms that has a
  positive or negative charge.
• Ionization Process that results in the
  formation of an ion.

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Ionization Energy

• The quantity of energy required to remove an
  electron from the gaseous atom or ion.

X (g) energy ? X (g) e-
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Periodic Trends

• First ionization energy
• increases from left to right across a period
• decreases going down a group.

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Consider step-ionization
1st ionization energy Al (g) energy ? Al
(g) e- I1 580 kJ/mole 2nd ionization
energy Al (g) energy ? Al2 (g) e- I2
1815 kJ/mole 3rd ionization energy Al2 (g)
energy ? Al3 (g) e- I3 2740
kJ/mole 4th ionization energy Al3 (g)
energy ? Al4 (g) e- I4 11600 kJ/mole
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• 2nd IE larger than 1st.
• Largest jump after removing
• outer shell (Valence) electrons.

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Electron Affinity

• Neutral atoms can also acquire electrons.

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Electron Affinity

• The energy change associated with the addition
  of an electron to a neutral atom.
• X(g) e? ? X?(g)

If addition of an electron is exothermic, then EA
is negative.
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• Some atoms must be forced to acquire an electron.
• When energy is absorbed, it is represented by a
  positive number.

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EA generally becomes more negative from L ? R
across a period. EA becomes more positive as
you go down a group. There are numerous
EXCEPTIONS!
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Second Electron Affinity

• Always positive.
• Always more difficult to add a 2nd electron to a
  negative ion.

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Ion An atom or group of atoms that has a
positive or negative charge.

• Positive ions cations
• Negative ions -- anions

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Size of Ions

• Absolute ion sizes Impossible to define.
• Mostly Interested in Trends
• A ? A e- smaller
• A e- ? A- larger

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Sizes of Ions Related to Positions of the
Elements in the Periodic Table
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Valence Electrons

• Electrons available to be lost, shared or gained
  in the formation of chemical compounds.
• They are the electrons in the highest energy
  levels.

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Electronegativity

• The ability of an atom in a molecule to attract
  shared electrons to itself.
• Electronegativity Ranges
• from 4.0 (Fluorine) to
• 0.7 (Cesium Francium).

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The Pauling Electronegativity Values
Electronegativity values range from 4.0 (F) to
0.7 (Cs).
The alkali metals and the alkaline-earth metals
are the least electronegative elements.