Effective Nuclear Charge (ENC)

1
Effective Nuclear Charge (ENC)

• Effective Nuclear Charge is the pull felt on the
  valence electrons by the protons in the nucleus
• How tightly the valence electrons are pulled by
  the nucleus determines how the element will react
  in forming ions

2
Inner Shell Shielding

• Inner shells (energy levels) of electrons
  shield or hide the valence electrons from the
  protons in the nucleus
• Magnesium has 12 protons
• Magnesium has 10 inner shell electrons
• The valence electrons only feel the pull of 2
  protons

3
Determining ENC

• ENC, in main group elements, is approximately
  equal to the number of valence electrons

4
Effects of Effective Nuclear Charge

• On
• Size
• Ionization Energy
• Electronegativity
• Electron Affinity

5
Size

• As ENC increases, the size decreases.
• Therefore, the size decreases as you go across
  the periodic table
• The size increases as you go down a family

6
Ionization Energy

• This is the amount of energy needed to remove an
  electron making a positive ion.
• Written as
• A energy -gt A e-
• As ENC increases, energy needed to remove an
  electron increases.
• Energy to remove subsequent electrons also
  increases

7
Electron Affinity

• This is the change in energy as an atom gains an
  electron making a negative ion.
• Written as
• A e- -gt A- energy
• As ENC increases, Electron Affinity increases.

8
Electronegativity

• The ability of an atom to attract electrons.
• As ENC increases, Electronegativity increases.

9
Ion size

• Positive (cat) ions get
• Smaller
• Negative (an) ions get
• Larger