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11/30/2016 Do Now What Ionization Energy Ionization Energy The ease with which valence electrons can be added/removed from an atom is an important factor in determining it’s chemical behavior 1st ionization energy, I1, is the energy needed to remove the 1st valence electron from an atom, forming a cation+1 I1 Na(g) → Na+1(g) + e- cathode? cation? anode? anion? Ionization Energy The ionization energy is the energy required to remove an electron from the ground state of the atom when it is a gas The greater the ionization energy, the more difficult it is to remove an electron Ionization Energy The is the charge of a(n): Ionization Energy 2nd ionization energy, I2, is the energy needed to remove the 2nd valence electron forming a cation+2, and so on… I2 Na+1(g) → Na+2(g) + e The 1 11/30/2016 Ionization Energy Ionization Energy that the ionization energies for the elements increase as additional electrons are removed: Notice I1 < I2 < I3 < … Why? As each additional electron is removed, the remaining electrons see a larger effective nuclear charge! Ionization Energy the huge increase in ionization energy that occurs when an core electron is removed: Note Na → Na+1 Na+1 → Na+2 I1 = 496 kJ/mol I2 = 4560 kJ/mol Mg → Mg+1 Mg+1 → Mg+2 I1 = 738 kJ/mol I2 = 1450 kJ/mol I3 = 7730 kJ/mol Mg+2 I2 → Mg+3 Ionization Energy Removal of core electrons require overcoming a much larger effective nuclear charge Why? Disturbing the stability of an octet Na+1: Na+2: Solution Problem Predict which of the 3 elements will have the largest I2, based on their position on the periodic table [Ne] = 2-8 2-7 greatest ionization energies involve the removal of core electrons The 2nd e- must be a core e The 1st e- must have been the only valence e The Therefore, we are looking for an element with 1 valence electron 2 11/30/2016 Solution That element is the one indicated in red, Na (4562 kJ/mol) Na (1145 kJ/mol) Ca (2251 kJ/mol) S Periodic Trends in Ionization Energies What trends do we observe in the ionization energies on the periodic table? Periodic Trends in Ionization Energies I increases with increasing atomic number as we move left to right within a period I decreases with increasing atomic number as we move top to bottom within a group Periodic Trends in Ionization Energies metals generally have low ionization energies compared with the nonmetals Why? Why are the values of I so high for the group 8A elements? The 3