1. 7.5 Electron Affinities By: Ginny Edwards, Rikin Marfatia, Dave Rodak, & Dave Nguyen

2. What Are Electron Affinities? Opposite of ionization energy Opposite of ionization energy Electron Affinity – The energy change resulting from an atom at neutral state gaining an electron and becoming an anion 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) ΔE = -349 kJ/mol Ex: Cl (g) + 1 e -  Cl - (g) ΔE = -349 kJ/mol Atom must be in a gaseous state 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 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 A more negative electron affinity also shows a stable ion will be formed

3. Periodic Trends (Groups) There aren’t very clear patterns but nevertheless there are some There aren’t very clear patterns but nevertheless there are some As you go down the group (column) the electron affinity decreases As you go down the group (column) the electron affinity decreases Placed in larger orbitals further away from the nucleus (less nuclear charge) Placed in larger orbitals further away from the nucleus (less nuclear charge) Decrease minimal due to a counterbalance Decrease minimal due to a counterbalance These values are all negative

4. Exceptions VIA and VIIA VIA and VIIA Oxygen and Fluorine have relatively lower electron affinities 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 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 Repulsion due to small volume Nitrogen, Noble Gases, and all IIA elements have a positive Electron Affinity Nitrogen, Noble Gases, and all IIA elements have a positive Electron Affinity

5. Periodic Trends (Period) From IIIA through VIIA, as you go across a period, an atom will release more energy to gain an electron 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 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 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 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 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) Have a filled “s” subshell, so adding an electron would place it alone in the “p” subshell (highly unfavorable)

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