IM11. Controversial Lewis structuresThere is sometimes debate in science. Discussion can be vital part of just how we arrive at a far better understanding that things. In the context of molecules and structures, there have actually been long-running controversies around how come draw details phosphorus and also sulfur compounds. A look at that dispute can tell us some things around how different chemists think about bonding.

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The controversy comes to how come draw, and also think about, the bonding in a variety of "high-valent" sulfur and also phosphorus compounds, in i m sorry the sulfur or phosphorus atom is bonded to much more than the usual number of neighbours.

Sulfate ion, SO42-, is an example of a high-valent sulfur compound. Sulfur, prefer oxygen, typically forms 2 bonds. In sulfate, the sulfur is attached to four different atoms.

We could draw that structure in 2 ways. A structure that obeys the octet ascendancy would have actually a solitary bond to each oxygen. That would fulfill the octet that sulfur. In bespeak to to fill in the right number of electrons for this group of atoms, every oxygen will have a an unfavorable formal charge. Sulfur will have a charge of plus two.


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


Can one atom have much more than eight electrons in its valence shell? lots of them can, if they are further down the regular table. Whether sulfur and phosphorus have the right to is much much less clear. Frequently, the reality that these are 3rd row atom is taken into consideration significant. After all, the d electrons begin in the third row. Maybe sulfur and phosphorus deserve to accommodate extra electrons since they have d orbitals. The d orbitals don"t have any electrons in them, yet, so possibly they deserve to accept some from various other aroms via bonds.


Many theoretical chemistry (including experts in sulfur and phosphorus chemistry) are persuaded that this scenario just isn"t possible. The d level in these atoms is just too high in energy. Various other atoms can"t probably donate electron to sulfur and phosphorus in this way.

And yet, many chemists (including some specialists in sulfur and phosphorus chemistry) still attract sulfate with dual bonds. Why would they make such a failure in the face of reason?

Partly, it has to do with experimental evidence. Remember, "experimental" sound wishy-washy and tentative come non-scientists, however to a chemist the term really method "reality-based". Among the reasons world draw twin bonds in numerous sulfur and also phosphorus compound is that the bonds simply behave like dual bonds. The is, they room stronger and much shorter than solitary bonds. We can not think around those bond in precisely the method we think about double bonds in various other situations, yet the experimental evidence says that there is some additional attraction between the sulfur and also oxygen atom in these cases.

There is added evidence the sulfur and also phosphorus can "exceed the octet" or form "Lewis-disobedient" structures. Compounds choose phosphorus pentafluoride (PF5) clearly require much more than 4 bonds to phosphorus. Without 5 bonds, us would require to draw one the the fluorides as an anion. It"s certainly possible that this could be the true structure, but there is evidence from X-ray crystallography that every one of the fluorines are attached come phosphorus in PF5, and also in the connected PF6- anion (hexafluorophosphate, a really common molecule ion in X-ray crystallographic studies).

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


Maybe we deserve to think around sulfate in a similar way. Are those S-O bond stronger because of a covalent dual bond, or space they stronger because the covalent shortcut is augmented by secondary ionic interaction in between the sulfur and also the oxygens?


So, sulfur and phosphorus yes, really can type additional bonds. The only true controversy around the octet preeminence in sulfur and phosphorus chemistry is a small too ethereal to explore really deeply at this point: it"s even if it is sulfur can type a covalent dual bond in this cases. The concern has to perform with ideas from molecular orbit theory, i m sorry is a later chapter, and how well d orbitals can type "pi bonds" v the p orbital on oxygen.

Problem IM11.1.

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


Problem IM11.2.

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

Problem IM11.3.

Many oxyphosphorus compound are typically drawn in a method that is inconsistent through the octet rule. Draw two structures for each of the following compounds: one that obeys the octet rule yet has higher charge separation, and one that has actually lower fee separation yet exceeds the octet ~ above phosphorus. (Note: in a few of the compounds, hydrogen is attached to 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 structures for each of the following compounds: one the obeys the octet rule however has greater charge separation, and also one that has actually lower charge separation yet 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 adhering to compounds: one that obeys the octet rule yet has greater charge separation, and also one that has actually lower charge separation but exceeds the octet top top 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 society but over there is no a good deal that controversy around it in the scientific community. A review of evidence can be uncovered at theNational Oceanic and Atmospheric Administration"s website.

Explain few of the evidence that an international warming is occurring and also is connected to human activity. Why perform you think over there is small debate around these ideas amongst scientists, but lots of debate in the us public as a whole?

This website is written and maintained by chris P. Schaller, Ph.D., university of Saint Benedict / Saint John"s university (with contributions from various other authors together noted). The is freely obtainable for educational use.

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Structure & Reactivity in Organic, Biological and Inorganic Chemistry by chris Schaller is licensed under a creative Commons Attribution-NonCommercial 3.0 Unported License.