The Main Groups

The most interesting point about the elements described in this chapter is the variety of properties that they exhibit. These six groups include elements that are nonmetals, metalloids, and metals, as well as elements that are solids, liquids, and gases at room temperature. 

You may be surprised to find out that you encounter many of these elements on a daily basis. Some of them are important for industry (such as silicon used in electronics) wherecis others, such as carbon and nitrogen, are important for biology. Also, don t forget the chlorine in swimming pools and helium in balloons. 

The chemistry of these sbc groups of elements is made similar by the presence of occupied p-orbitals, which control much of the chemistry and material properties. For example, the difference between diamond and graphite can be understood in terms of the presence of sp (this is read aloud as s-p-three) carbon atoms found in a diamond compared to sp carbon atoms found in the graphite of pencil lead (it s not actually made of lead). The sp carbon atoms have one unbonded electron in the outer shell, giving graphite the capacity for conduction of electricity because that electron can flow more freely, compared the fact that all the electron in diamond crystal are used for covalent bonding. 

Ptacinq Main Groan Elements on the Periodic Tame 

The periodic table is built on a simple idea The activity of atoms is related to the number of valence electrons (electrons capable of participating in bonding for more on valence electrons, check out Chapter 7) in the outer orbitals. All of the atoms in the same column (or group) on the periodic table have the same number of valence electrons in their outer orbital, and, therefore, exhibit similar behavior when reacting with other elements. 

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Carbon hydrides are commonly called hydroearbons. They are very numerous and the study of these compounds is outside the seope of this book. Reference will therefore be made only to the main groups. 

It is immediately obvious that the transition metals are more dense, harder, and have higher melting points and boiling points than the main group metals (for example, the metals of Group II,... 

Reactions with Orgunometullic Compounds of the Main Group Metals via Transmetallation... 

V. Chvalovsky, in B. J. Aylett, ed., Organometallic derivatives of the Main Group Elements, Butterworths, London, 1975. 

Table 1.2, based on Modern Plastics sources, provides USA consumption figures (based on sales data) for the main groups of plastics materials. The figures probably underestimate the global importance of the major tonnage thermoplastics since these are also manufactured in quantity in developing countries and OPEC countries. 

Hydrogen combines with many elements to form binary hydrides MH (or M H ). All the main-group elements except the noble gases and perhaps indium and thallium form hydrides, as do all the lanthanoids and actinoids that have been studied. Hydrides are also formed by the more electropositive transition elements, notably Sc, Y, La, Ac Ti, Zr, Hf and to a lesser... 

E. Coates, M. L. H. Green and K. Wade, Organo-meiallh Compounds, Vol. 1. The Main Group Elements, 3rd edn Chap. It. Group II. pp. 71-121. Methuen. London. 1967... 

H. Hoffmann and M. Becke-Goehring, Topics in Phosphorus Chemistry 8, 193-271 (1976) J. G. Riess in A. H. Cowley (ed.), Rings, Clusters and Polymers of the Main Group Elements, ACS Symposium Series No. 232, 17-47 (1983). 

Organosilanes are the main group of coupling agents for glass fiber-reinforced polymers. They have been developed to couple virtually any polymer to the minerals that are used in reinforced composites f42J. 

The main groups used in such estimates are as shown in Table 1.3. 

Hellwinkel, D. Penta- and.Hexaorganyl Derivatives of the Main Group Elements. 109, 1-63... 

The charges of ions formed by atoms of the main-group elements can be predicted by applying a simple principle ... 

The atomic radii of the main-group elements are shown at the top of Figure 6.13 (p. 153). Notice that, in general, atomic radii—... 

Atomic and ionic radii of the main-group elements. Negative ions are always larger than atoms of the same element, whereas positive ions are always smaller than atoms of the same element. ... 

The radii of cations and anions derived from atoms of the main-group elements are shown at the bottom of Figure 6.13. The trends referred to previously for atomic radii are dearly visible with ionic radius as well. Notice, for example, that ionic radius increases moving down a group in the periodic table. Moreover the radii of both cations (left) and anions (right) decrease from left to right across a period. 

Ionization energies of the main-group elements are listed in Figure 6.15. Notice that ionization energy—... 

These structures (without the circles) are referred to as Lewis structures. In writing Lewis structures, only the valence electrons written above are shown, because they are the ones that participate in covalent bonding. For the main-group elements, the only ones dealt with here, the number of valence electrons is equal to the last digit of the group number in the periodic table (Table 7.1). Notice that elements in a given main group all have the same number of valence electrons. This explains why such elements behave similarly when they react to form covalently bonded species. 

Essentially all transition metal ions behave like Zn2+, forming a weakly acidic solution. Among the main-group cations, Al3+ and, to a lesser extent, Mg2+, act as weak acids. In contrast the cations in Group 1 show little or no tendency to react with water. 

In previous chapters we have referred from time to time to compounds of the transition metals. Many of these have relatively simple formulas such as CuSO CrCI3, and FetNO These compounds are ionic The transition metal is present as a simple cation (Cu2+, Cr3+, Fe3+). In that sense, they resemble the ionic compounds formed by the main-group metals, such as CaS04 and AKNOJ ... 

EDTA forms 1 1 complexes with a large number of cations, including those of some of the main-group metals. The complex formed by calcium with EDTA is used to treat lead poisoning. When a... 

Four of the main-group cations are essential in human nutrition (Table A). Of these, the most important is Ca2+. About 90% of the calcium in the body is found in bones and teeth, largely in the form of hydroxyapatite, CatOH)2 - SCa PO. Calcium ions in bones and teeth exchange readily with those in the blood about 0.6 g of Ca2+ enters and leaves your bones every day. In a normal adult this exchange is in balance, but in elderly people, particularly women, there is sometimes a net loss of bone calcium, leading to the disease known as osteoporosis. 

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