Group 8A

The similarity, then, between carbene and carbyne complex chemistry of Group 8a transition metals, as well as of Group 6a and 7a metals, is apparent. 

The development of the chemistry of carbene complexes of the Group 8a metals, Ru, Os, and Ir, parallels chemistry realized initially with transition metals from Groups 6 and 7. The pioneering studies of E. O. Fischer and co-workers have led to the characterization of many hundreds of carbene complexes in which the heteroatoms N, O, and S are bonded to the carbene carbon atoms. The first carbene ligands coordinated to Ru, Os, and Ir centers also contained substituents based on these heteroatoms, and in this section the preparation and properties of N-, O-, S-, and Se-substituted carbene complexes of these metals are detailed. 

The noble gases in order of increasing radii are He < Ne < Ar < Kr < Xe < Rn. The size increases as one goes down Group 8A, because the outer electrons which set their size exist in electron clouds that become farther from the nucleus. 

Neon has eight valence electrons and all of them are paired, hence the valence orbitals of neon are completely filled. Therefore neon is very unreactive and does not bond with any other element. Similarly, the group 8A elements (noble gases) helium and argon are very unreactive. However, krypton and xenon may form bonds under certain conditions. 

Group 8A—Noble gases Helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn) are gases of very low reactivity. Helium, neon, and argon don t combine with any other element krypton and xenon combine with very few. 

We ll see in later chapters that redox reactions are common for almost every element in the periodic table except for the noble gas elements of group 8A. In general, metals act as reducing agents, and reactive nonmetals such as O2 and the halogens act as oxidizing agents. 

FIGURE 5.1 Agraph of atomic radius in picometers (pm) versus atomic number shows a rise-and-fall pattern of periodicity. The maxima occur for atoms of group 1A elements (Li, Na, K, Rb, Cs, Fr) the minima occur for atoms of the group 7A elements. Accurate data are not available for the group 8A elements. 

The success of these and other predictions convinced chemists of the usefulness of Mendeleev s periodic table and led to its wide acceptance. Even Mendeleev made some mistakes, though. He was completely unaware of the existence of the group 8A elements—He, Ne, Ar, Kr, Xe, and Rn—because none were known at the time. All are colorless, odorless gases with little or no chemical reactivity, and none were discovered until 1894, when argon was first isolated. 

Though sometimes referred to as "rare gases" or "inert gases," these older names are not really accurate because the group 8A elements are neither rare nor completely inert. Argon, for instance, makes up nearly 1% by volume of dry air, and there are several dozen known compounds of krypton and xenon, although none occur naturally. Some properties of the noble gases are listed in Table 6.8. 

Group 8A (noble gas) elements are essentially inert they rarely gain or lose electrons. 

Group 8A elements (noble gases), such as neon, rarely form covalent bonds because they already have valence-shell octets. 

When we classify the elements as metals and nonmetals we see that metals occupy very big part (about 80%) of the periodic table. The elements in B groups (transition elements, actinides and lanthanides) and the elements in the groups, 1 A, 2A and 3A (except hydrogen and boron) are metals. Only the eleven elements H, C, N, O, R S, Se, F, Cl, Br and I are nonmetals and the elements in group 8A are noble gases. However, among these elements, B, Si, Ge, As, Sb, Te, Po and At are metalloids and Sn, Pb and Bi and Be have metallic properties. 

Noble gases The elements helium, neon, argon, krypton, xenon and radon. Family of inactive gases found in group 8A of the periodic table. 

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