Criticism
Both the term and concept of hypervalency still fall under criticism. In 1984, in response to this general controversy, Paul von Ragué Schleyer proposed the replacement of 'hypervalency' with use of the term hypercoordination because this term does not imply any mode of chemical bonding and the question could thus be avoided altogether.
The concept itself has been criticized by Ronald Gillespie who, based on an analysis of electron localization functions, wrote in 2002 that "as there is no fundamental difference between the bonds in hypervalent and non-hypervalent (Lewis octet) molecules there is no reason to continue to use the term hypervalent."
For hypercoordinated molecules with electronegative ligands such as PF5 it has been demonstrated that the ligands can pull away enough electron density from the central atom so that its net content is again 8 electrons or fewer. Consistent with this alternative view is the finding that hypercoordinated molecules based on fluorine ligands, for example PF5 do not have hydride counterparts e.g. phosphorane PH5 which is an unstable molecule.
Even an ionic model holds up well in thermochemical calculations. It predicts favorable exothermic formation of PF4+F− from phosphorus trifluoride PF3 and fluorine F2 whereas a similar reaction forming PH4+H− is not favorable.
Read more about this topic: Hypervalent Molecule
Famous quotes containing the word criticism:
“Like speaks to like only; labor to labor, philosophy to philosophy, criticism to criticism, poetry to poetry. Literature speaks how much still to the past, how little to the future, how much to the East, how little to the West.”
—Henry David Thoreau (1817–1862)
“The critic lives at second hand. He writes about. The poem, the novel, or the play must be given to him; criticism exists by the grace of other men’s genius. By virtue of style, criticism can itself become literature. But usually this occurs only when the writer is acting as critic of his own work or as outrider to his own poetics, when the criticism of Coleridge is work in progress or that of T.S. Eliot propaganda.”
—George Steiner (b. 1929)
“I hold with the old-fashioned criticism that Browning is not really a poet, that he has all the gifts but the one needful and the pearls without the string; rather one should say raw nuggets and rough diamonds.”
—Gerard Manley Hopkins (1844–1889)