Plumbous compounds

Plumbo-. plumbous, plumbo-, lcad(II). -salz, n. plumbous salt, lead (II) salt, -verbindung, /. plumbous compound, lead(II) compoimd. plump, a. bulky, clumsy, gross. 

PlumUo compounds (see lead). Plumbous compounds (see Lera). Poly acid alcohols, 270. 

When lead does take part in a chemical reaction, it demonstrates one of two oxidation states, 4+ and 2+. Compounds of the former class are known as lead(IV) or plumbic compounds, while those of the latter class are lead(n) or plumbous compounds. Like aluminum, lead is amphoteric and will react with strong bases. The products of such reactions are known as plumbates and plumbites. 

A comparison of the structural chemistry of these two elements reveals some interesting resemblances and also some remarkable differences. The atoms of each element have the same outer electronic structure, two s and two p electrons, and each has oxidation states of 2 and 4. The more metallic nature of lead is shown by the difference between the structures of the elements (Chapter 29) and by many differences between stannous and plumbous compounds. It will be convenient to deal first with Sn(iv) and Pb(iv) since the structural chemistry is more straightforward for the higher oxidation state. Few compounds of Sn(ii) and Pb(ii) are isostructural and compounds containing these metals in both oxidation states are different for the two elements (e.g. Sn2S3 and Pb304). 

Other divalent plumbous compounds are used in more specialized applications lead II nitrate, Pb(N03)2, and lead II chloride, PbCh, are used as oxidizing agents (fluxes) in plumbing, soldering and tinning of metals. Lead II acetate, (CH3COO)2Pb, and basic lead II acetate, (CH3COO)2Pb.Pb(OH)2 are both used in the modern production of white lead. 

With the exception of the nitrate and the acetate all plumbous compounds are insoluble in water. 

Lead forms two series of compounds corresponding to the oxidation states of +2 and +4. The +2 state is the more common. Compounds of lead(IV) are regarded as covalent, those of lead(II) as primarily ionic. Lead is amphoteric, forming plumbous (Pb(II)) and plumbic (Pb(IV)) salts as well as plumbites and plumbates, respectively. 

Both fin and lead from Group IV can form valency two and four compounds. Two of the four outer electrons can behave as inert when the atoms are bivalent. Bivalent tin (stannous) derivatives are covalent whereas the nitrate and sulphate of bivalent lead (plumbous) are ionic. Some tetavalent compounds such as the hydrides and chloride are unstable, e.g. ... 

Lead forms amphoteric compounds in +2 and +4 valence states, forming plumbous and plumbic salts, such as PbCL and PbCL, as well as plumbites and plumbates, such as Na4Pb03 and Ca2Pb04,. Over a thousand compounds of lead are known which include divalent and tetravalent salts, complexes, and organometaUics. Divalent compounds of lead are far more numerous than the tetravalent compounds. Most compounds, however, result from the reactions involving other lead compounds, rather than elemental lead. Only the reactions involving elemental lead are outlined briefly below. 

Plumbous salts of these compounds are very sensitive to mechanical and thermal... 

From their infra-red absorption spectra he ascribes a quinonoid structure to the first two compounds and a diazo structure to the last two and to their plumbous salts ... 

Often the color of compound is different from that of the ions into which it might be dissociated thus lead iodide is yellow, although both plumbous ion and iodide ion are colorless. In 1918 Bichowsky,41 in a paper dealing with valence colors of atoms, suggested that this change in color is the result of the sharing of electrons between bonded atoms, and this idea has been extended by Pitzer and Hildebrand,48 who proposed the postulate that the extent of deviation of the color of a compound from that of the ions into which it might dissociate may be taken as a measure of the deviation of the bonds from pure ionic bonds. 

Lead was originally known by its Latin name of plumbum, from which its modern chemical symbol (Pb) is derived. The Latin name is still preserved also in the common names for lead compounds, as in plumbic and plumbous chlorides. 

No one is quite sure how lead got its name. The word has been traced to manuscripts that date to before the 12th century. Romans called the metal plumbum. It is from this name that the element s chemical symbol comes Pb. Compounds of lead are sometimes called by this old name, such as plumbous chloride. 

PliunMo compounds ( Lead). Plumbous ooia pounds (aw Lead). Polyacid alcohol, 270. 

In Table 9.3 the results suggest that the absolute value of the atomic charge in plumbic oxides Pb02 are larger than those in plumbous oxides PbO. However, all the lead xygen crystals are very far from purely ionic compounds. 

---