IM11. Controversial Lewis structuresThere is sometimes dispute in science. Debate can be crucial part of how we arrive at a far better understanding that things. In the paper definition of molecules and also structures, there have been long-running controversies about how come draw certain phosphorus and sulfur compounds. A look at that conflict can tell united state some things about how different chemists think around bonding.

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The controversy involves how to draw, and also think about, the bonding in a number of "high-valent" sulfur and also phosphorus compounds, in which the sulfur or phosphorus atom is external inspection to more than the usual variety of neighbours.

Sulfate ion, SO42-, is an instance of a high-valent sulfur compound. Sulfur, prefer oxygen, generally forms 2 bonds. In sulfate, the sulfur is attached come four various atoms.

We can draw that structure in two ways. A framework that obeys the octet preeminence would have a single bond to each oxygen. That would fulfill the octet the sulfur. In stimulate to to fill in the right number of electrons for this group of atoms, each oxygen will have a an adverse formal charge. Sulfur will have actually a charge of plus two.


A different method to attract the structure would include twin bonds between sulfur and also two of the oxygen atoms. That framework would have actually less charge separation than the various other structure. However, the sulfur would have twelve electrons in that is valence shell, not eight. It would certainly exceed its octet.


Can one atom have more than eight electrons in the valence shell? several them can, if castle are further down the periodic table. Whether sulfur and phosphorus have the right to is much much less clear. Frequently, the truth that this are 3rd row atoms is considered significant. After all, the d electrons start in the third row. Perhaps sulfur and also phosphorus have the right to accommodate extra electrons due to the fact that they have d orbitals. The d orbitals don"t have any kind of electrons in them, yet, so possibly they can accept some from various other aroms via bonds.


Many theoretical chemists (including professionals in sulfur and also phosphorus chemistry) are encouraged that this scenario just isn"t possible. The d level in these atoms is simply too high in energy. Various other atoms can"t possibly donate electrons to sulfur and also phosphorus in this way.

And yet, numerous chemists (including some specialists in sulfur and also phosphorus chemistry) still attract sulfate with twin bonds. Why would certainly they make such a mistake in the face of reason?

Partly, it needs to do with speculative evidence. Remember, "experimental" sounds wishy-washy and also tentative to non-scientists, however to a chemist the term really means "reality-based". Among the reasons world draw dual bonds in numerous sulfur and also phosphorus compound is that the bonds just behave like dual bonds. The is, they are stronger and much shorter than single bonds. We might not think about those bonds in exactly the means we think about dual bonds in other situations, yet the experimental evidence says that there is some added attraction in between the sulfur and oxygen atom in these cases.

There is added evidence that sulfur and phosphorus deserve to "exceed the octet" or form "Lewis-disobedient" structures. Compounds choose phosphorus pentafluoride (PF5) plainly require much more than four bonds to phosphorus. Without 5 bonds, us would require to attract one the the fluorides as an anion. It"s certainly possible that this can be the true structure, however there is evidence from X-ray crystallography that all of the fluorines space attached to phosphorus in PF5, as well as in the connected PF6- anion (hexafluorophosphate, a very common molecule ion in X-ray crystallographic studies).

But those instances can likewise be attracted in various other ways. Space all five of the fluorines in PF5 really covalently bound, or are few of them ionic? We can draw this framework in different ways, too.


Maybe we have the right to think around sulfate in a comparable way. Are those S-O binding stronger since of a covalent twin bond, or room they stronger because the covalent link is augmented by an additional ionic interaction in between the sulfur and the oxygens?


So, sulfur and phosphorus yes, really can form additional bonds. The just true controversy around the octet preeminence in sulfur and phosphorus chemistry is a small too subtle to explore really deeply in ~ this point: it"s whether sulfur can type a covalent double bond in these cases. The concern has to execute with concepts from molecular orbit theory, i m sorry is a later chapter, and how fine d orbitals can form "pi bonds" v the p orbital ~ above oxygen.

Problem IM11.1.

Fill in any missing lone pairs on the complying with structures.


Problem IM11.2.

Indicate whether every of the structures in IM11.1. Obeys the octet rule. If not, carry out a resonance structure that obeys the octet rule.

Problem IM11.3.

Many oxyphosphorus compounds are typically drawn in a method that is inconsistent through the octet rule. Attract two structures for each of the adhering to compounds: one that obeys the octet rule but has greater charge separation, and one that has lower charge separation however exceeds the octet on phosphorus. (Note: in a couple of of the compounds, hydrogen is attached come phosphorus, as suggested in the condensed formula.)

a) H3PO4 or PO(OH)3 b) H3PO3 or HPO(OH)2 c) H3PO2 or H2PO(OH)

d) (CH3)3PO e) (CH3O)PO

Problem IM11.4.

Draw two frameworks for each of the adhering to compounds: one that obeys the octet rule but has greater charge separation, and one that has lower charge separation but exceeds the octet on chlorine.

a) hypochlorite, ClO- b) chlorite, ClO2- c) chlorate, ClO3- d) perchlorate, ClO4-

Problem IM11.5.

Draw two frameworks for each of the following compounds: one the obeys the octet rule but has higher charge separation, and one that has actually lower charge separation however exceeds the octet ~ above sulfur.

a) sulfite, SO32- b) sulfate, SO42- c) thiosulfate, S2O32-

d) disulfate, S2O72- e) persulfate or peroxomonosulfate, SO52-

Problem IM11.6.

Global warming is a controversial subject in culture but there is not a great deal that controversy about it in the scientific community. A review of proof can be discovered at theNational Oceanic and Atmospheric Administration"s website.

Explain few of the evidence that global warming is occurring and is linked to human activity. Why execute you think there is little debate about these ideas amongst scientists, yet lots of debate in the us public together a whole?

This website is written and also maintained by chris P. Schaller, Ph.D., university of Saint Benedict / Saint John"s college (with contribute from various other authors as noted). That is freely accessible for educational use.

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Structure & Reactivity in Organic, Biological and also Inorganic Chemistry by chris Schaller is license is granted under a an innovative Commons Attribution-NonCommercial 3.0 Unported License.