Lead metal properties

Tin finds widespread use beeause of its resistanee to eorrosion, or as foil or to provide proteetive eoats/plates for other metals. Properties of lead whieh make industrial applieation attraetive surround its soft, plastie nature permitting it to be rolled into sheets or extruded through dies. In the finely-divided state lead powder is pyrophorie in bulk form the rapidly-formed proteetive oxide layer inhibits further reaetion. It dissolves slowly in mineral aeids. Industrial uses inelude roofing material, piping, and vessel linings, e.g. for aeid storage. 

The Group 1 elements are soft, low-melting metals which crystallize with bee lattices. All are silvery-white except caesium which is golden yellow "- in fact, caesium is one of only three metallic elements which are intensely coloured, the other two being copper and gold (see also pp. 112, 1177, 1232). Lithium is harder than sodium but softer than lead. Atomic properties are summarized in Table 4.1 and general physical properties are in Table 4.2. Further physical properties of the alkali metals, together with a review of the chemical properties and industrial applications of the metals in the molten state are in ref. 11. 

Elements on the left of the p block, especially the heavier elements, have ionization energies that are low enough for these elements to have some of the metallic properties of the members of the s block. However, the ionization energies of the p-block metals are quite high, and they are less reactive than those in the s block. The elements aluminum, tin, and lead, which are important construction materials, all lie in this region of the periodic table (Fig. 1.61). 

The elements show increasing metallic character down the group (Table 14.6). Carbon has definite nonmetallic properties it forms covalent compounds with nonmetals and ionic compounds with metals. The oxides of carbon and silicon are acidic. Germanium is a typical metalloid in that it exhibits metallic or nonmetallic properties according to the other element present in the compound. Tin and, even more so, lead have definite metallic properties. However, even though tin is classified as a metal, it is not far from the metalloids in the periodic table, and it does have some amphoteric properties. For example, tin reacts with both hot concentrated hydrochloric acid and hot alkali ... 

Metals are insoluble in common liquid solvents but can dissolve in each other (like dissolves like). A mixture of substances with metallic properties is called an alloy. Some alloys are true solutions, but microscopic views show that others are heterogeneous mixtures. Brass, for instance, is a homogeneous solution of copper (20 to 97%) and zinc (80 to 3%), but common plumber s solder is a heterogeneous alloy of lead (67%) and tin (33%). When solder is examined under a microscope, separate regions of solid lead and solid tin can be seen. When brass is examined, no such regions can be detected. 

When it comes to metal-rich compounds of the alkaline earth and alkali metals with their pronounced valence electron deficiencies it is no surprise that both principles play a dominant role. In addition, there is no capability for bonding of a ligand shell around the cluster cores. The discrete and condensed clusters of group 1 and 2 metals therefore are bare, a fact which leads to extended inter-cluster bonding and results in electronic delocalization and metallic properties for all known compounds. 

A corollary is the question of how many individuals it takes to form a collectivity and to display the collective properties how many molecules of water to have a boiling point, how many atoms to form a metal, how many components to display a phase transition Or, how do boiling point, metallic properties, phase transition etc. depend on and vary with the number of components and the nature of their interac-tion(s) In principle any finite number of components leads to a collective behavior that is only an approximation, however dose it may well be, an asymptotic approach to the true value of a given property for an infinite number of units. 

For example, at a ratio of molecular iodine to tetrathiatetracene (TTT) of 1 2, mixtures of iodides (TTT)i(I)i and (TTT)2(I)3 can be obtained on fast cooling. Slow cooling of the same component mixture in the same proportion leads to the single product (TTT)2(I)3. The latter is just the product that possesses metallic properties. Sometimes, even at nonstoichiometric ratio, salts of the 1 1 composition are formed. Interaction between TTF and TCNQ can be exemplified. To obtain the 2 1 composition, an indirect synthesis is appropriate. The synthesis is based on an exchange reaction of the following type ... 

Electrocrystallization with M B( 5135)4 under the same conditions leads to the single crystals of alkali-metal salts M C5q(T33F)j, (x 0.4, y 2.2) with M = Na, Li, K, Cs. They are isomorphic and crystallize with hexagonal unit-cells. In contrast to the PPN-salt the Na salt with the structure NaQ39C5o(THF)2 2 shows metallic properties [85, 86]. The resistivity of this compound was measured to be 50 S cm at room temperature and about 1000 S cm at 100 K. The lattice spacing of about 9.9 A at room temperature indicates a direct Cjq-Cjq interaction, which could explain the salt s metallic character. 

Moreover, the mixed valence of copper, Cu(II) - Cu(III), is absolutely necessary for the delocalization of holes in the copper oxygen framework, leading to semi-metallic or metallic properties. 

In the fourth group, carbon and silicon are both non-metallic, while germanium has a very small electrical conductivity. It is only with white tin and lead that the electrical conductivity approaches the normal values for true metals. In the fifth group, arsenic and antimony are just on the limit between metallic and non-metallic properties, while of the elements of the sixth group, only polonium might be considered to have real metallic properties. The halogens, in the seventh group, show no trace of metallic properties. 

The political justification for transition metal cluster chemistry is the assumption that clusters are models in which metallic properties may be more easily studied than in the metals themselves. These properties include electronic phenomena such as color and conductivities as well as surface phenomena, such as atom arrangements and catalytic activities. Thus, there are two main lines of cluster research. The more academic line leads to the search for new types of clusters and their structure and bonding, whereas the more practical line leads to the investigation of reactivities with the hope that clusters may open catalytic pathways that neither plain metals nor mononuclear catalysts can provide. The interdependence of both lines is obvious. 

Another hazy boundary separates polymeric and metallic substances. We have already noted the case of iodine, which can be described as a molecular solid but which might also be viewed as a two-dimensional polymer having incipient metallic properties. Elemental tellurium, whose chain structure was described earlier in this section, has pronounced metallic properties. Each Te atom is bonded to two others at a distance of 284 pm, and this connectivity leads to a helical chain. However, each Te atom is bonded to four more in other chains, at a distance of 350 pm. These longer Te-Te contacts are apparently responsible for the metallic properties. 

Abstract This chapter provides an overview of the luminescence properties of plat-inum(II) complexes, exploring how the excited states involved in emission are influenced by the ligands around the metal ion. The square planar nature of d8 Pt(II) complexes has many implications, leading to properties and applications that are not open to d6 complexes. For example, axial intermolecular interactions can lead to new excited states not present in the isolated molecules. This review focuses on complexes containing one or... 

The behaviour of the polarized reflectivity and optical conductivity spectra of new quasi-two-dimensional organic conductor p -(BEDO-TTF)5[CsHg(SCN)4]2 versus temperature for E L and E1. L are quite different. For E . L, the temperature changes of R(ro) and ct(co) are due to the decrease of the optical relaxation constant of the free carriers as expected for a metal. For E L at temperatures below 200 K, the energy gaps in the ct(co) spectra at about 4000 cm 1 and at frequencies below 700 cm 1 appear simultaneously with the two new bands of ag vibrations of the BEDO-TTF molecule activated by EMV coupling. This suggests a dimerization of the BEDO-TTF molecules in the stacks, which leads to a metal-semiconductor transition.. In the direction perpendicular to L, the studied salt shows metallic properties due to a very favourable overlap of the BEDO-TTF molecular orbitals. 

Another difficulty is met with in adsorption on metallic surfaces. Metals, or rather conducting bodies, are considered as adsorbents with an ideal polarizability. Accepting this view as true does not make it clear whether the metallic properties leading to this ideal polarizability should be assumed to start at the outer peripheries of the surface atoms of the metal or whether we must assume these properties to be found from a plane through the centers of the surface atoms. The choice of the outer boundary of the region of conducting electrons is very important, however, for the assessment of the distance of the adsorbed atom to the metal. 

As seen from Table 4 no localized moments are found in compounds containing d1 and d2 cations. This is indicative of metallic properties in the case of the d1 compounds and also in the case of d2 compounds with only small distortions of the anion octahedra. The high value of cja in the case of TiS and VP favours a low-lying d level which, doubly occupied, would lead to temperature-independent paramagnetism or diamagnetism, too. However, localized d electrons are not very likely in Ti ions and the experiment supports this view (92, 96). 

Another distorted variant of the NiAs structure occurs in NiP which is stable only above 850° C (159). In the orthorhombic NiP structure the distortions are stronger than in the MnP type (Fig. 44) but like in MnP the metal atoms form zig-zag chains with Ni—Ni = 2.53 A. The coordination of the nickel atoms is modified insofar as they are shifted towards a comer of the distorted anion octahedra. As a result there are only five phosphorus atoms in contact with the central nickel atom. The anions themselves are arranged in pairs with a P—P distance of 2.43 A, which roughly corresponds to the length of a half bond. In the absence of cation-cation bonds the P—P pairs would lead to divalent Ni and non-metallic properties would be possible. In the actual structure the Ni—Ni bonds exclude semiconductivity which, moreover, cannot be expected in a high-temperature phase. 

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