Values and Trends
- Main article: Molar ionization energies of the elements
Generally the (n+1)th ionization energy is larger than the nth ionization energy. Always, the next ionization energy involves removing an electron from an orbital closer to the nucleus. Electrons in the closer orbitals experience greater forces of electrostatic attraction; thus, their removal requires increasingly more energy. Ionization energy becomes greater up and to the right of the periodic table.
Some values for elements of the third period are given in the following table:
| Element | First | Second | Third | Fourth | Fifth | Sixth | Seventh |
|---|---|---|---|---|---|---|---|
| Na | 496 | 4,560 | |||||
| Mg | 738 | 1,450 | 7,730 | ||||
| Al | 577 | 1,816 | 2,881 | 11,600 | |||
| Si | 786 | 1,577 | 3,228 | 4,354 | 16,100 | ||
| P | 1,060 | 1,890 | 2,905 | 4,950 | 6,270 | 21,200 | |
| S | 999.6 | 2,260 | 3,375 | 4,565 | 6,950 | 8,490 | 27,107 |
| Cl | 1,256 | 2,295 | 3,850 | 5,160 | 6,560 | 9,360 | 11,000 |
| Ar | 1,520 | 2,665 | 3,945 | 5,770 | 7,230 | 8,780 | 12,000 |
Large jumps in the successive molar ionization energies occur when passing noble gas configurations. For example, as can be seen in the table above, the first two molar ionization energies of magnesium (stripping the two 3s electrons from a magnesium atom) are much smaller than the third, which requires stripping off a 2p electron from the very stable neon configuration of Mg2+.
Ionization energy is also a periodic trend within the periodic table organization. Moving left to right within a period or upward within a group, the first ionization energy generally increases. As the atomic radius decreases, it becomes harder to remove an electron that is closer to a more positively charged nucleus. Ionization energy increases from left to right in a period and decreases from top to bottom in a group.
Read more about this topic: Ionization Energy
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