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the type of hybrid orbitals used by the central atom in TeF4.

The angle between electron pairs in a tetrahedral arrangement is 109.5°. However, although H2O is indeed angular and NH3 is trigonal pyramidal, the angles between the bonds are 104° and 107°, respectively. In a sense, such close agreement is quite satisfactory for so simple an approach, but clearly there is more to explain. To account for variations in bond angle, it is supposed that electron pair repulsions are greatest between lone pairs, less between lone pairs and bonding pairs, and least between bonding pairs. The justification of this ordering has proved somewhat elusive; qualitatively it is presumed that lone pairs, being attached only to a single centre, spread over a greater volume than bonding pairs, which are pinned between two attracting centres. Whatever the reason may be, the order correlates quite well with observation. Thus, in H2O the two lone pairs move apart a little, and the two bonding pairs move away from them by closing the angle between one another. Likewise, in NH3 the three bonding pairs move back from the single lone pair to minimize their interaction with it. As a result, the H―N―H bond angle decreases slightly. In each case, the predicted angle is less than the tetrahedral angle, as is observed experimentally.

VSEPR theory is quite successful at predicting (or at least rationalizing) the overall shapes of molecules. Thus, the hypervalent species SF6 (sulfur hexafluoride), with six bonding pairs, is predicted and found to be a regular octahedron, and PCl5 (phosphorus pentachloride), with five bonding pairs, is predicted and found to be a trigonal bipyramid. The XeF4 (xenon tetrafluoride) molecule is hypervalent with six electron pairs around the central xenon (Xe) atom. These pairs adopt an octahedral arrangement. Four of the pairs are bonding pairs, and two are lone pairs. According to VSEPR theory, the repulsion between the lone pairs is minimized if they lie on opposite sides of the xenon atom, leaving the four equatorial pairs as bonding pairs.

VSEPR theory: xenon tetrafluoride molecule

This analysis suggests that XeF4 should be a planar species, which is found to be the case.