7.5 Electron Affinities

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7.5 Electron Affinities

• By Ginny Edwards, Rikin Marfatia, Dave Rodak,
  Dave Nguyen

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What Are Electron Affinities?

• Opposite of ionization energy
• Electron Affinity The energy change resulting
  from an atom at neutral state gaining an electron
  and becoming an anion
• Ex Cl(g) 1 e- ? Cl-(g) ?E -349 kJ/mol
• Atom must be in a gaseous state
• The greater the attraction between the atom and
  the added electron, the more negative the
  electron affinity will be
• A more negative electron affinity also shows a
  stable ion will be formed

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Periodic Trends (Groups)

• There arent very clear patterns but nevertheless
  there are some
• As you go down the group (column) the electron
  affinity decreases
• Placed in larger orbitals further away from the
  nucleus (less nuclear charge)
• Decrease minimal due to a counterbalance

These values are all negative
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Exceptions

• VIA and VIIA
• Oxygen and Fluorine have relatively lower
  electron affinities
• These two atoms have a high force of repulsion,
  making an added electron more unfavorable than
  with Sulfur and Chlorine
• Repulsion due to small volume
• Nitrogen, Noble Gases, and all IIA elements have
  a positive Electron Affinity

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Periodic Trends (Period)

• From IIIA through VIIA, as you go across a
  period, an atom will release more energy to gain
  an electron
• The closer you get to the noble gases, the more
  filled your valence orbitals will become
• IA elements release energy to gain an electron,
  but not easily
• Noble Gases are very stable atoms, therefore
  their electron affinity is close to zero they do
  not accept electrons easily
• IIA atoms are similar to the Noble Gases in terms
  of electron affinity
• Have a filled s subshell, so adding an electron
  would place it alone in the p subshell (highly
  unfavorable)

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Periodic Trends (Period) Cont.

• VA group is similar to IIA
• p subshell has all occupied orbitals (1
  electron each)
• Being half-filled, these elements are more stable
  than IVA and VIA elements
• Representative Elements
• Generally, the electron affinity gets more
  negative as you go across the representative
  elements