The ionization energies of sodium (in kJ/mol), starting withthe first and ending

Question

The ionization energies of sodium (in kJ/mol), starting withthe first and ending with the eleventh, are 495.9, 4560, 6900,9540, 13,400, 16,600, 20,120, 25,490, 28,930, 141,360, 170,000.Plot the log of ionization energy (y axis) versus the number ofionization (x axis); for example, log 495.9 is plotted versus 1(labeled I1, the first ionization energy), log4560 is plotted versus 2 (labeled I2, thesecond ionization energy), and so on. Label I1through I11 with the electrons in orbitals suchas 1s, 2s, 2p, and 3s. What can you deduce about electronshellsfrom the breaks in the curve? The ionization energies of sodium (in kJ/mol), starting withthe first and ending with the eleventh, are 495.9, 4560, 6900,9540, 13,400, 16,600, 20,120, 25,490, 28,930, 141,360, 170,000.Plot the log of ionization energy (y axis) versus the number ofionization (x axis); for example, log 495.9 is plotted versus 1(labeled I1, the first ionization energy), log4560 is plotted versus 2 (labeled I2, thesecond ionization energy), and so on. Label I1through I11 with the electrons in orbitals suchas 1s, 2s, 2p, and 3s. What can you deduce about electronshellsfrom the breaks in the curve?

Explanation / Answer

Without me actually doing the graph (this is your homeworkafter all and we don't need it), we can deduce that there existelectron shells (energy levels) for an atom. We know this becauseof the energy it takes to remove electrons. We expect thatelectrons in shells closer to the nucleus, which is highlypositively charged, will be more difficult to remove (there existsa strong coulombic attraction between the nucleus and theseelectrons). Sure enough, as we "the number of ionization"increases, the ionization energy tends to increase. Consider the first one, 495kJ/mol. This is the value requiredto remove the 3s1 electron. To remove the next electron,it takes A LOT more energy. This must mean that this electron is ina new shell, which is closer to the nucleus and more stabilized. Dowe freqently see Na2+? No, because it requires such alarge amount of energy to remove that second electron, which isfrom the 2p6 shell. Additionally, removing an electronfrom a stable full shell is highly unfavourable due to exchangeenergy (you may not have learnt this yet). The 2p shell must hold 6electrons, because when we get down to the last one (the2p1) electron, it takes very little energy to remove it(20kJ/mol). This is because it is now the only electron in thatshell. It is essentially the new valence electron. Continue in thismanner to "deduce" where the next shell begins...Essentially, shellboundaries occur at breaks in the curve of your graph.

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