Editing Ionization energy (section)

====Ionization energy increases when====
* Reaching Group 18 [[noble gas]] elements: This is due to their complete electron subshells,<ref>{{cite book |last1=Singh |first1=Jasvinder |chapter=Inert Gases |page=122 |chapter-url=https://books.google.com/books?id=eKnrhryjqn0C&pg=PA122 |title=Sterling Dictionary of Physics |date=1999 |publisher=Sterling Publishers Pvt. Ltd |isbn=978-81-7359-124-2 }}</ref> so that these elements require large amounts of energy to remove one electron.
* Group 12: The elements here, zinc ({{nuclide|Zn|&nbsp;}}: 9.4 eV), [[cadmium]] ({{nuclide|Cd|&nbsp;}}: 9.0 eV) and [[mercury (element)|mercury]] ({{nuclide|Hg|&nbsp;}}: 10.4 eV) all record sudden rising IE values in contrast to their preceding elements: [[copper]] ({{nuclide|Cu|&nbsp;}}: 7.7 eV), [[silver]] ({{nuclide|Ag|&nbsp;}}: 7.6 eV) and [[gold]] ({{nuclide|Au|&nbsp;}}: 9.2 eV), respectively. For mercury, it can be extrapolated that the [[relativistic quantum chemistry|relativistic]] stabilization of the 6s electrons increases the ionization energy, in addition to poor shielding by 4f electrons that increases the effective nuclear charge on the outer valence electrons. In addition, the closed-subshells electron configurations: [Ar] 3d<sup>10</sup> 4s<sup>2</sup>, [Kr] 4d<sup>10</sup>5s<sup>2</sup> and [Xe] 4f<sup>14</sup> 5d<sup>10</sup> 6s<sup>2</sup> provide increased stability.
* Special case: shift from [[rhodium]] ({{nuclide|Rh|&nbsp;}}: 7.5 eV) to [[palladium]] ({{nuclide|Pd|&nbsp;}}: 8.3 eV). Unlike other Group 10 elements, palladium has a higher ionization energy than the preceding atom, due to its electron configuration. In contrast to [[nickel]]'s [Ar] 3d<sup>8</sup> 4s<sup>2</sup>, and [[platinum]]'s [Xe] 4f<sup>14</sup> 5d<sup>9</sup> 6s<sup>1</sup>, palladium's electron configuration is [Kr] 4d<sup>10</sup> 5s<sup>0</sup> (even though the [[Aufbau principle#Exceptions to the rule in the transition metal|Madelung rule]] predicts [Kr] 4d<sup>8</sup> 5s<sup>2</sup>). Finally, [[silver]]'s lower IE ({{nuclide|Ag|&nbsp;}}: 7.6 eV) further accentuates the high value for palladium; the single added s electron is removed with a lower ionization energy than palladium,<ref>{{cite book |doi=10.1016/B978-0-7506-3365-9.50028-6 |chapter=Vanadium, Niobium and Tantalum |title=Chemistry of the Elements |year=1997 |pages=976–1001 |isbn=978-0-7506-3365-9 }}</ref> which emphasizes palladium's high IE (as shown in the above linear table values for IE)
* The IE of [[gadolinium]] ({{nuclide|Gd|&nbsp;}}: 6.15 eV) is somewhat higher than both the preceding ({{nuclide|Sm|&nbsp;}}: 5.64 eV), ({{nuclide|Eu|&nbsp;}}: 5.67 eV) and following elements ({{nuclide|Tb|&nbsp;}}: 5.86 eV), ({{nuclide|Dy|&nbsp;}}: 5.94 eV). This anomaly is due to the fact that gadolinium valence d-subshell borrows 1 electron from the valence f-subshell. Now the valence subshell is the d-subshell, and due to the poor shielding of positive nuclear charge by electrons of the f-subshell, the electron of the valence d-subshell experiences a greater attraction to the nucleus, therefore increasing the energy required to remove the (outermost) valence electron.
* Moving into d-block elements: The elements Sc with a 3d<sup>1</sup> electronic configuration has a ''higher'' IP ({{nuclide|Sc|&nbsp;}}: 6.56 eV) than the preceding element ({{nuclide|Ca|&nbsp;}}: 6.11 eV), contrary to the decreases on moving into s-block and p-block elements. The 4s and 3d electrons have similar shielding ability: the 3d orbital forms part of the n=3 shell whose average position is closer to the nucleus than the 4s orbital and the n=4 shell, but electrons in s orbitals experience greater penetration into the nucleus than electrons in d orbitals. So the mutual shielding of 3d and 4s electrons is weak, and the effective nuclear charge acting on the ionized electron is relatively large. Yttrium ({{nuclide|Y|&nbsp;}}) similarly has a higher IP (6.22 eV) than {{nuclide|Sr|&nbsp;}}: 5.69 eV.
* Moving into f-block elements; The elements ({{nuclide|La|&nbsp;}}: 5.18 eV) and ({{nuclide|Ac|&nbsp;}}: 5.17 eV) have only very slightly lower IP's than their preceding elements ({{nuclide|Ba|&nbsp;}}: 5.21 eV) and ({{nuclide|Ra|&nbsp;}}: 5.18 eV), though their atoms are anomalies in that they add a d-electron rather than an f-electron. As can be seen in the above graph for ionization energies, the sharp rise in IE values from ({{nuclide|Cs|&nbsp;}}: 3.89 eV) to ({{nuclide|Ba|&nbsp;}}: 5.21 eV) is followed by a small increase (with some fluctuations) as the f-block proceeds from {{nuclide|Ba|&nbsp;}} to {{nuclide|Yb|&nbsp;}}. This is due to the [[lanthanide contraction]] (for lanthanides).<ref name=Housecroft>{{cite book |last1=Housecroft |first1=C.E. |last2=Sharpe |first2=A.G. |date=November 1, 1993 |title=Inorganic Chemistry |url=https://www.pearson.com/us/higher-education/program/Housecroft-Inorganic-Chemistry-5th-Edition/PGM2178749.html |type=eBook |language=en |volume=3 |edition=15th |location=Switzerland |publisher=Pearson Prentice-Hall |publication-date=November 1, 1993 |pages=536, 649, 743 |doi=10.1021/ed070pA304.1 |isbn=978-0-273-74275-3 |archive-url=https://web.archive.org/web/20210414235943/https://www.pearson.com/us/higher-education/program/Housecroft-Inorganic-Chemistry-5th-Edition/PGM2178749.html |archive-date=April 14, 2021 |access-date=December 14, 2020 |url-status=bot: unknown }}</ref><ref name=Cotton>{{Cotton&Wilkinson5th|pages=776, 955}}</ref><ref name=Jolly>{{cite journal |doi=10.1021/ed062pA137.1 |title=Modern Inorganic Chemistry (Jolly, William L.) |year=1985 |last1=Billo |first1=E. J. |journal=Journal of Chemical Education |volume=62 |issue=4 |pages=A137 |bibcode=1985JChEd..62..137B |doi-access=free }}</ref> This decrease in ionic radius is associated with an increase in ionization energy in turn increases, since the two properties correlate to each other.<ref name=":1" /> As for d-block elements, the electrons are added in an inner shell, so that no new shells are formed. The shape of the added orbitals prevents them from penetrating to the nucleus so that the electrons occupying them have less shielding capacity.