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Electron Affinity Trends - Electron affinity decreases or...

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Electron Affinity Trends Electron Affinity is the energy associated with the addition of an electon to a gaseous atom. Example: Cl (g) + e - Cl - (g) E.A. = -349 kJ/mole Notice the sign on the energy is negative. This is because energy is usually  released  in this process, as apposed  to ionization energy, which requires  energy. A  more negative  electron affinity corresponds to  greater  attraction for an electron. (An unbound electron has an energy of zero.) Trends: As with ionization energy, there are two rules that govern the periodic trends of electron affinities: Electron affinity becomes less negative down a group. As the principal quantum number increases, the size of the orbital increases and the affinity for the electron is  less. The change is small and there are many exceptions.
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Unformatted text preview: Electron affinity decreases or increases across a period depending on electronic configuration. This occurs because of the same subshell rule that governs ionization energies. Example: Since a half-filled "p" subshell is more stable, carbon has a greater affinity for an electron than nitrogen. Obviously, the halogens, which are one electron away from a noble gas electron configuration, have high affinities for electrons: (More negative energy = greater affinity) Element Electron Affinity I-295.2 kJ/mole Br-324.5 kJ/mole Cl-348.7 kJ/mole F *-327.8 kJ/mole * Fluorine's electron affinity is smaller than chlorine's because of the higher electron - electron repulsions in the smaller 2p orbital compared to the larger 3p orbital of chlorine....
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