Shielding	Atomic radii definition
Atomic radii trends	Atomic radii notes
Ionic radii	Ionization Energy
Electron Affinity	Electronegativity

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Ionization Energy

• Energy required to completely remove one electron from a gaseous atom
  • always endothermic, requires energy
  • successive ionizations are higher in energy
    • increasing positive charge makes removing next electron more difficult
• General Trends
  • IE generally increases left to right across a period (some exceptions! see below)
    • increaseing effective nuclear charge (Zeff) makes removal more difficult
  • IE generally decreases down a group
    • valence electron is in higher energy orbital that is further from the nucleus and therefore more easily removed

 

Atomic Radius:

• Increases down the group
  • valence electrons placed in orbitals with increasing n
    
    
• Decreases across (left to right) the period (esp. within s- and p-block)
  • electrons placed in orbitals within same level
  • nuclear charge increases steadily since electrons in same shell are unable to screen efficiently
    
    

• Note the following trend of atomic radii for group 6 metals:

  Cr 1.29 angs., Mo 1.40 angs, W 1.41 angs.

  Is this unusual? What is occurring?

Ionic Radii

• Cations
  • smaller radii than neutral, isoelectronic atom
  • As charge increases, the radius decreases
    • increased nuclear charge has stronger attraction for electron
    • reduced electron-electron repulsions
• Anions
  • radius increases with greater negative charge
    • increased electron-electron repulsions

• Lanthanide contraction :
  • second and third row transition metals have nearly the same radii
    • 4f orbitals are filled and provide poor shielding
    • Zeff increase offsets expected increase in radii

Electronegativity:

• X is the ability of a atom to attract electron density to itself within a bond.
  • Atoms with high electronegativities will attract more electron density to itself
  • electronegativities may be used to determine bond polarity
    
    
• Atoms with low electronegativity are termed electropositive
  
  
• Electronegativity will increase with increasing oxidation state

• Several Electronegativity scales have been developed
  • the best known is Pauling's scale based on thermodynamic data
  • Muliken's relates electronegativity to the average of the ionization energy and electron affinity
    
    
• Trends in Electronegativity
  • Increases left to right across a period
  • Decreases down a group

Electron Affinity

• Energy change that occurs when a gaseous negative ion releases an electron
  • can be thought of as the ionization energy of an anion.
  • value may be positive or negative (endothermic or exothermic)
  • the more negative the value, the more favorable the process
    
    
• Trends mimic that of ionization energy
  • EA generally increases left to right across a period (more negative and fav.)
  • EA generally decreases down a group (less negative and less favorable)