Lone pair



A lone pair is a bonding electrons equal the total number of valence electrons from a compound.

A single lone pair can be found with atoms in the hydrochloric acid.

Angle Changes

The pairs often exhibit a hydrogen ion.


This can be seen more clearly when looked at in two more common molecules. For example methane (CH4) has an angle between the hydrogens of 109.5o, whereas in water (H2O) the angle between the hydrogens is just 104.5 o. As you can clearly see, if lone pairs are present (in water there are two) then the other hydrogens are pushed further away to a point where there is the least repulsion from the lone pair but also from the other electrons. That's an illustration of the VSEPR theory.

Unusual lone pairs

A stereochemically active lone pair is also expected for divalent tin ions due to their formal electronic configuration of ns2. In the solid state this results in the distorted metal coordination observed in the litharge structure adopted by both PbO and SnO. The formation of these heavy metal ns2 lone pairs which was previously attributed to intra-atomic hybridization of the metal s and p states[1] has recently been shown to have a strong anion dependence[2]. This dependence on the electronic states of the anion can explain why some divalent lead and tin materials such as PbS and SnTe show no stereochemical evidence of the lone pair and adopt the symmetric rocksalt crystal structure[3],[4].


In molecular systems the lone pair can also result in a distortion in the coordination of ligands around the metal ion. The lead lone pair effect can be observed in supramolecular complexes of inhibited.


isonitrile groups based on interaction with germaniums empty 4p orbital [6]

See also

References

  1. ^ Stereochemistry of Ionic Solids J.D.Dunitz and L.E.Orgel, Advan. Inorg. and Radiochem. 1960, 2, 1-60
  2. ^ Electronic origins of structural distortions in post-transition metal oxides: experimental and theoretical evidence for a revision of the lone pair model D.J.Payne, R.G.Egdell, A.Walsh, G.W.Watson, J.Guo, P.-A.Glans, T.Learmonth and K.E.Smith, Phys. Rev. Lett. 2006, 96, 157403 doi:10.1103/PhysRevLett.96.157403
  3. ^ The origin of the stereochemically active Pb(II) lone pair: DFT calculations on PbO and PbS A.Walsh and G.W.Watson, J. Sol. Stat. Chem. 2005, 178, 5 doi:10.1016/j.jssc.2005.01.030
  4. ^ Influence of the Anion on Lone Pair Formation in Sn(II) Monochalcogenides: A DFT Study A.Walsh and G.W.Watson, J. Phys. Chem. B 2005, 109, 18868 doi:10.1021/jp051822r
  5. ^ Is an Electronic Shield at the Molecular Origin of Lead Poisoning? A Computational Modeling Experiment C.Gourlaouen and O.Parisel Angew. Chem. Int. Ed. 2007, 46, 553 –556 doi:10.1002/anie.200603037
  6. ^ Lewis base induced tuning of the Ge–Ge bond order in a digermyne G.H.Spikes and P.P.Power Chem. Commun., 2007, 85 - 87, doi:10.1039/b612202g
 
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