Aluminum valence

The chemical behavior of Group III elements carrying three organic groups is very greatly influenced by the electron deficiency of the aluminum valency shell. The absence of one electron pair has the result that trialkyl derivatives of these elements react extremely easily with oxygen and other electron donors. 

Aluminum oxide is amphoteric and can react as either an acid or a base. I/ Aluminum valence is +3. 

In a generalized sense, acids are electron pair acceptors. They include both protic (Bronsted) acids and Lewis acids such as AlCb and BF3 that have an electron-deficient central metal atom. Consequently, there is a priori no difference between Bronsted (protic) and Lewis acids. In extending the concept of superacidity to Lewis acid halides, those stronger than anhydrous aluminum chloride (the most commonly used Friedel-Crafts acid) are considered super Lewis acids. These superacidic Lewis acids include such higher-valence fluorides as antimony, arsenic, tantalum, niobium, and bismuth pentafluorides. Superacidity encompasses both very strong Bronsted and Lewis acids and their conjugate acid systems. 

A typical absorption curve for vitreous siUca containing metallic impurities after x-ray irradiation is shown in Eigure 12. As shown, the primary absorption centers are at 550, 300, and between 220 and 215 nm. The 550-nm band results from a center consisting of an interstitial alkah cation associated with a network substituent of lower valency than siUcon, eg, aluminum (205). Only alkaUes contribute to the coloration at 550 nm. Lithium is more effective than sodium, and sodium more effective than potassium. Pure siUca doped with aluminum alone shows virtually no coloration after irradiation. The intensity of the band is deterrnined by the component that is present in lower concentration. The presence of hydrogen does not appear to contribute to the 550-nm color-center production (209). 

In insulating oxides, ionic defects arise from the presence of impurities of different valence from the host cation. An aluminum ion impurity substituting in a magnesium oxide [1309-48-4] MgO, hostlattice creates Mg vacancies. 

If we continue to remove electrons from aluminum, we discover a very large increase in ionization energy when the fourth electron is removed. Again this is because the fourth electron must be withdrawn from a 2p orbital, an orbital much lower on the energy level diagram. We conclude that three electrons, the two 35 and the one 3p, are more easily removed than the others. Since aluminum has three easily removed electrons, aluminum is said to have three valence electrons. 

Aluminum, silicon, and sulfur are close together in the same row of the periodic table, yet their electrical conductivities are widely different. Aluminum is a metal silicon has much lower conductivity and is called a semiconductor sulfur has such low conductivity it is called an insulator. Explain these differences in terms of valence orbital occupancy. 

Write out the electron configuration of sodium, magnesium, and aluminum and find the ionization energies for all their valence electrons (Table 20-IV, p. 374). Account for the trend in the heats of vaporization and boiling points (Table 20-1) of these elements. Compare your discussion with that given in Section 17-1.3. 

We can tell from the ionization energy of aluminum that this atom holds its second and third valence electrons rather firmly. With this fact in mind, we can see why aluminum hydroxide, Al(OH)3, would not be as strongly basic as are the hydroxides, NaOH and Mg(OH>2. Aluminum hydroxide has extremely low solubility in neutral aqueous solutions but does react with strong acids according to the reaction... 

The effect of small valence and large coordination number is further shown by the observation that silicon tetrahedra, which share comers only with aluminum octahedra, share edges with magnesium octahedra (in olivine, chondrodite, humite, clinohumite) and with zirconium polyhedra with coordination number eight (in zircon). 

The electrostatic valence rule1) is approximately satisfied, deviations of not being allowed. Sharing of polyhedra must consequently be such as to have each OH or F common to two octahedra or attached to one silicon or aluminum tetrahedron only, and each 0 common to two silicon tetrahedra, four aluminum octahedra, two octahedra and one silicon tetrahedron, two or three octahedra and one aluminum tetrahedron, etc. structures with 0= common to three silicon tetrahedra or to one silicon tetrahedron and three octahedra are not satisfactory. 

Agreement with the electrostatic valence rule is satisfactory except for the oxygen atoms G (Fig. 4), common to only three oc-tahedra. It is seen, however, that these atoms occur in groups of four, which can be combined to tetra-hedra by placing aluminum ions in positions 4e, the total bond strengths then becoming 2 . The four chlorine ions occupy positions 4 c, 4 b being ruled out by the small Cl -0= distance it leads to (2.72 A, sum of radii 3.21 A). 

In connection with a discussion of alloys of aluminum and zinc (Pauling, 1949) it was pointed out that an element present in very small quantity in solid solution in another element would have a tendency to assume the valence of the second element. The upper straight line in Fig. 2 is drawn between the value of the lattice constant for pure lead and that calculated for thallium with valence 2-14, equal to that of lead in the state of the pure element. It is seen that it passes through the experimental values of aQ for the alloys with 4-9 and 11-2 atomic percent thallium, thus supporting the suggestion that in these dilute alloys thallium has assumed the same valence as its solvent, lead. 

Each of these elements (boron and aluminum) has three valence electrons. Therefore, each of these elements can comfortably form three bonds ... 

In the compounds shown above, boron and aluminum are using their valence electrons to form bonds, but notice that neither one has an octet. Each element is capable of forming a fourth bond in order to obtain an octet, but then each element will bear a formal charge of -1. 

Aluminum, in Group 13, has three valence electrons. The configurations show three electrons with a — 3, so the configuration is consistent with the valence electron count. 

Whereas the other blocks contain only metals, elemental properties vary widely within the p block. We have already noted that aluminum (3 3 p ) can lose its three valence electrons to form AP cations. Draw a right triangle in... 

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