2.4B: Isoelectronic Molecules
- Page ID
- 2540
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Isoelectronic Species Periodic Trends
The observation that isoelectronic species are usually isostructural, first made by Penny and Southerland in 1936, known as the isoelectronic principle (Geoff). Table 1 shows an example of isostructural isoelectronic species periodic trends. All of these molecules are octahedral and isoelectronic within their periods.
Isostructural Isoelectronic Species in Differeing Groups and Periods
| Table 1 | Group 13 | Group 14 | Group 15 | Group 16 | Group 17 |
| Period 3 | AlF63- | SiF62- | PF6- | SF6 | ClF6+ |
| Period 4 | GaF63- | GeF62- | AsF6- | SeF6 | BrF6+ |
| Period 5 | InF63- | SnF62- | SbF6- | TeF6 | IF6+ |
Other interesting trends appear in the periodic table including:
- Isoelectronic matricies--all isoelectronic species in a matrix defined by total electrons and valence electrons vary by progression in group number. For example, a 14 electron/10 valence electron diatomic matrix would have molecules such as CN-, CO, and N2.
- Isoelectronic arrays--an atom is replaced with another which alters the charge and continues the isoelectronic relationship. For example: BeF42-, BF4-, and CF4.
References
- Smith, Michael, and Jerry March. March's Advanced Organic Chemistry: Reactions, Mechanisms, and Structure. Hoboken, NJ: Wiley-Interscience, 2007.
- Rayner-Canham, Geoff. "Isoelectronic Series: a Fundamental Periodic Property." Foundations of Chemistry 11.2 (2009): 123-29.
Problems
1) Why is it important to understand the term "isoelectronic" and its trends throughout the periodic table?
2) Which isoelectronic species has the largest radius?
a. Mg2+ b.N3- c. O2- d. F-
3) Name 3 isostructural molecules
Answers:
1) Isoelectronic can help predict chemical reactions and interactions between molecules.
2) N3-
3) AlF63-, SiF62-, PF6-