Why These Elements

We now discuss just why these elements out of the entire periodic table have been selected. One thing is clear — they were not only selected as a function of their abundance and their availability in the universe as well as in the earth s crust, and the oceans (which constitute the major proportion of the earth s surface), but also on the basis of their suitability for the functions that they are called upon to play, in what is predominantly an aqueous environment."  

These halides are all of the general formula MX2, a fact that demonstrates once again the degree to which the +2 oxidation state dominates the chemistry of these elements. (See Chapter 8 for an extended thermochemical discussion of why these elements do not form either MX or MX3 salts.) 

Draw electron-dot symbols for the nonmetallic elements and use them to explain why these elements form the bonding patterns listed in Table 3.1. 

Half of the first 18 elements have an odd number of electrons, and half have an even number. Show why these elements aren t half paramagnetic and half diamagnetic. 

Down any group (vertical column), the properties of elements tend to be remarkably similar, which is why these elements are said to be grouped or in a family. As Figure 2.28 shows, several groups have traditional names that 

The large dip in the PDOS of Mo and other transition metals with half-filled d bands is actually the reason why these elements possess a bcc structure. Systems typically prefer an atomic structure that leads to 

Look at the table of electron configurations in Appendix C. Which elements have configurations that are exceptions to the aufbau principle Propose a reason why these elements have these exceptions. 

Nickel catalysts used in steam reforming are more resistant to deactivation by carbon deposition if the surface contains sulfur, or gold. Explain why these elements act as promoters. Would you prefer sulfur or gold as a promoter Explain your answer. 

Recycling of rare earths is until recently rarely undertaken in practice (Binnemans and Jones 2014 Graedel et al. 2011). Marshall (2014) points out several reasons why. These elements are present in only very small amounts in things like cell phones, and, as parts get smaller, so do the amounts of material used. In a touch screen, the elements are distributed throughout the material at the molecular level, and thus are not present as separate parts. 

Iron, cobalt, and nickel are similar in properties and are sometimes studied together as the iron triad. For example, each is a fairly active metal that reacts with acids to give hydrogen and the -1-2 ions. In addition to the -1-2 ions, the -1-3 ions of the metals also figure prominently in the chemistries of the elements. Explain why these elements are similar. 

In the case of animals, the absence or very low level of an essential element may lead to poor development, sickness and, in case of total absence, to death. For example, if the diet of a chicken is deficient in manganese, its eggs do not hatch, and manganese deficiency is also said to lead to sterility. This is the reason why these elements are deliberately added in feed formulations.  

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