Phosphorus nonbonding electron pairs

The N—>P dative bonds are weak and different in lengths (1.800 A on average), and the triflate anions are effectively extended to consider interaction with the counter ion. Again the phosphorus atom is strongly pyramidalized and features the aspects of an inert nonbonding electron pair. 

What is the expected formula of a covalent compound formed between phosphorus and hydrogen that uses one atom of phosphorus (b) How many bonding electron pairs and how many nonbonding electron pairs are in one molecule of this compound ... 

How many nonbonding electron pairs are there per atom in chlorine, sulfur, phosphorus, and silicon ... 

Figure 12.20 By drawing Lewis structures you can show that there are three (chlorine), two (sulfur), one (phosphorus), and zero (silicon) nonbonding electron pairs per atom.

In many of their complexes PF3 and PPI13 (for example) resemble CO (p. 926) and this at one time encouraged the belief that their bonding capabilities were influenced not only by the factors (p. 198) which affect the stability of the a P M interaction which uses the lone-pair of elecU"ons on p and a vacant orbital on M, but also by the possibility of synergic n back-donation from a nonbonding d , pair of electrons on the metal into a vacant 3d , orbital on P. It is, however, not clear to what extent, if any, the a and n bonds reinforce each other, and more recent descriptions are based on an MO approach which uses all (cr and n) orbitals of appropriate symmeU"y on both the phosphine and the metal-containing moiety. To the extent that a and n bonding effects on the stability of metal-phosphorus bonds can be isolated from each otlier and from steric factors (see below) the accepted sequence of effects is as follows ... 

A Lewis base must have valence electrons available for bond formation. Any molecule whose Lewis stmcture shows nonbonding electrons can act as a Lewis base. Ammonia, phosphorus trichloride, and dimethyl ether, each of which contains lone pairs, are Lewis bases. Anions can also act as Lewis bases. In the first example of adduct formation above, the fluoride ion, with eight valence electrons in its 2 s and 2 p orbitals, acts as a Lewis base. 

Compare the molecules phosphorus trichloride (PCI3) and dichloromonoxide (CI2O). How many pairs of electrons surround the central atom How many of these pairs are bonding Nonbonding What are the shapes of the molecules ... 

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