Valence covering electron pair repulsion theory is a simple way of rationalising the forms of plenty of compounds in i beg your pardon a key group element is surrounding by ligands. ClF3 is a good illustration of this theory.

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The standard application the VSEPR concept to this molecule is as follows:

Central atom: invernessgangshow.netlorineValence electron on central atom: 7Three fluorine atom contribute: 1 eainvernessgangshow.netTotal: 10 = five electron pairs.The greatest repulsion is between any type of two “lone electron pairs”, causing these moving apart as as possiblethe next highest possible is between one lone pair and a shortcut pairthe shortest is in between two shortcut pairs.

 As used to invernessgangshow.netlorine trifluoride, it results in a trigonal bipyramidal geometry for the shape-determining five electron pairs. Among the trigonal positions is inhabited by the pair deriving from a Cl-F bond (F=white, Cl=red below). The various other two trigonal positions are occupied by 2 sets that electron lone pairs (yellow below) at ≥ 120° (rule 5, however more and the repulsions in between the lone pair and the trigonal Cl-F link would end up being too great, ascendancy 6 above). The continuing to be two Cl-F bond pairs occupy the di-axial location (rule 7 above).


The over at the very least is the typical “text-book” picture. Regular readers of this blog might have noted that I often like to question the message books. So here goes. My concern is with the over explanation, of 5 electron pairs all connected in some way with the main atom. An broadened octet in various other words. Well, if you take a look at earlier blogs, girlfriend may have observed that this expanded octet is not real (IMHO). If it’s no real, then we cannot be taking care of five electron pairs. Can VSEPR work with only eight electron in this instance? and also what room the collaborates of the so-called two “lone pairs”: is the angle subtended at the Cl by them yes, really trigonal (~120)?

I start with computing an accurate wavefunction, using the DFT-based ωB97XD/6-311++G(d,p)<1>. The electron count and also the coordinates of the localised containers will be obtained using ELF (Electron localisation function).

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Click because that 3D

The electron containers are presented here together red spheres; 8 and 9 space the “lone pairs”, together it happens a very reasonable description since the populaces for these space 2.07e. The 8-2-9 edge of 154° results from dominance 5 above; lone pairs repel greatly. Indeed, one might practically describe 8 and 9 as being di-axial. In i beg your pardon case, the geometry is not that of a trigonal bipyramid but is closer to the of a square pyramid.Basin 7 is a Cl-F bond, through a populace of 0.87e, rather less than a “pair” (the Wiberg bond index is 0.82).Other features include eg the orientation that the “lone pairs” top top fluorines 3 and 4, in i m sorry e.g. 16 is oriented anti-periplanar come the 2-1 bond. This is in fact an anomeric effect! one NBO evaluation reveals E(2) in between Lp16 and also σ*2-1 to be 6.3 kcal/mol, a relatively weak yet still a real anomeric interaction.The total electron counting for the ELF basins surrounding the main Cl is 6.84, no 10 together was comprise in the straightforward argument set out above.

VSEPR concept is a extremely simplified way of looking at the geometric origins of this odd tiny molecule; one ELF analysis an in similar way paints just a partial picture. Indeed, it appears doubtful that any simple way of regarding this varieties can ever be entirely adequate. Yet we should be mindful that the “EP” (electron pair) of VSEPR can itself be rather misleading in perpetuating the idea the main group facets contain broadened octets. However the geometry the invernessgangshow.netlorine trifluoride makes sense without imposing 10 valence electrons on the invernessgangshow.netlorine ~ all!