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By Ricky, Rahul, Tommy Doyle, Matt and Adam Snow

By Ricky, Rahul, Tommy Doyle, Matt and Adam Snow. The Basics . Definition: The energy change that occurs when an electron is acquired by a neutral atom is called the atom's electron affinity. Most atoms release energy when they acquire and  an electron A+ e-     A-+ energy

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By Ricky, Rahul, Tommy Doyle, Matt and Adam Snow

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  1. By Ricky, Rahul, Tommy Doyle, Matt and Adam Snow

  2. The Basics • Definition: The energy change that occurs when an electron is acquired by a neutral atom is called the atom's electron affinity. • Most atoms release energy when they acquire and  an electron • A+ e-    A-+ energy • Electron affinity is measured in kilojoules per mole.

  3. The Basics Continued... • In some cases, atoms must be "forced" to gain an electron  by the addition of energy. • A+ e- + energy                               A- • The quantity of the energy absorbed is always a positive number. • However, this configuration is extremely unstable and will loose an electron spontaneously.

  4. Period Trends • As electrons add to the same to the same p sublevel of atoms with increasing nuclear charge, electron affinities become more negative across the p block. • Since all atoms want to become stable, it is easier to add electrons to unstable ions rather than stable ions. • Therefore, it is easier to add an electron to Carbon [He] 2s2 2p2 than Nitrogen [He] 2s2 2p3. For Nitrogen we would have to add energy, and that would make it unstable.

  5. Period Trends

  6. General Rule-electrons add with greater difficulty down a group • This rule is the result of: • there is a slight increase in effective nuclear charge down a group, which increases electron affinities        2. there is an increase in atomic radius down a group, which decreases electron affinities • Effect 2usually predominates, so the rule usually works • There are exceptions such as: • the radius can be the same size or decrease down a group        2.  especially in heavy transition metals Group Trends

  7. AT A GLANCE Electron Affinity Increases Electron Affinity Increases

  8. Adding Electrons to Negatively Charged Ions • It is very hard to add electrons to negative charged ions • Therefore, electron affinities are all positive • Certain p block nonmetals tend to form ions that have noble-gas configurations • Once the ion reaches the “stable” configuration of a noble gas or any other stable configurations, it is hard to add more electrons

  9. Adding Electrons to Negatively Charged Ions Original Configuration Group 16- O : [He] 2s22p4 Group 17- Cl : [Ne]3s23p6 Group 16- O2-: [He] 2s22p6 Group 17- Cl- : [Ne]3s23p6

  10. THE END

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