Block metal chemistry the heavier metals

Chapter 21 dealt with descriptive chemistiy of the first row fi -block metals and, in this chapter, we focus on the second and third row metals (the heavier metals). Reasons for discussing the lighter and heavier metals separately were given in Sectimi 21.1. 

Lanthanum, La, is commonly classified with the lantha-noids (see Fig. 1.14) even though lanthanoid means like lanthanum and La is strictly a group 3 metal. Because of the chemical similarity of La to the elements Ce—Lu, they are considered together in Chapter 27. The only mention of La in this chapter is its occurrence. 

Niobium (formerly called columbium) and tantalum occur together in the mineral columbite (Fe,Mn)(Nb,Ta)20g. When the mineral is Nb-rich, it is called niobite and when Ta-rich, tantalite. Fusion of the ore with alkali gives poly-niobates and -tantalates, and further treatment with dilute acid yields Nb205 and Ta205. One method of separation utilizes the more basic character of Ta at a controlled concentration of HF and KF in aqueous solution, the oxides are converted to K2[NbOF5] and K2[TaFy]. The former is more water-soluble than the latter. The modem separation technique is fractional extraction firom aqueous HF solution into 

The platinum-group metals Rh, Pd and Pt play a vital role in keeping the environment devoid of pollutants originating from vehicle exhausts. They are present in catalytic converters (which we discuss in detail in Section 25.8) where they catalyse the conversion of hydrocarbon wastes, CO and NO. (see Box 15.7) to CO2, H2O and N2. In 2008, the manufacture of catalytic converters used 81% of the rhodium, 47% of palladium and 44% of platinum consumed worldwide. The growth rate of environmental catalyst manufacture by companies such as Johnson Matthey in the UK is driven by legislative measures for the control of exhaust emissions. Regulations in force in the US and Europe have had a major impact on the levels of emissions and have improved the quality of urban air. Tighter control of vehicle emissions has now been introduced in most parts of Asia. 

Catalytic converters showing interior design. Small particles (fs1600pm diameter) of Pd, Pt or Rh are dispersed on a support such as 7-alumina. 

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CHAPTER 22 cZ-Block metal chemistry the heavier metals... 

CHAPTER 22 of-Block metal chemistry the heavier metals Table 22.2 Mo—Mo bond lengths and orders in selected dimolybdenum species. 

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