Compounds Group IIIA elements

In this chapter, a brief summary of studies that made use of calorimetry to characterize compounds comprising group IIIA elements (zeolites, nitrides, and oxides catalysts) was presented. It was demonstrated that adsorption microcalorimetry can be used as an efficient technique to characterize the acid-base strength of different types of materials and to provide information consistent with the catalytic data. 

Generally speaking most of the shallow impurity levels which we shall encounter are based on substitution by an impurity atom for one of the host atoms. An atom must also occupy an interstitial site to be a shallow impurity. In fact, interstitial lithium in silicon has been reported to act as a shallow donor level. All of the impurities associated with shallow impurity levels are not always located at the substitutional sites, but a part of the impurities are at interstitial sites. Indeed, about 90% of group-VA elements and boron implanted into Si almost certainly take up substitutional sites i.e., they replace atoms of the host lattice, but the remaining atoms of 10% are at interstitial sites. About 30% of the implanted atoms of group-IIIA elements except boron are located at either a substitutional site or an interstitial site, and the other 40% atoms exist at unspecified sites in Si [3]. The location of the impurity atoms in the semiconductors substitutional, interstitial, or other site, is a matter of considerable concern to us, because the electric property depends on whether they are at the substitutional, interstitial, or other sites. The number of possible impurity configurations is doubled when we consider even substitutional impurities in a compound semiconductor such as ZnO and gallium arsenide instead of an elemental semiconductor such as Si [4],... 

B. Most covalent compounds of the Group IIIA elements, especially boron, B. The IIIA elements contain only three valence shell electrons, so they often form three covalent bonds when they bond to three other atoms. We therefore use six electrons as the number needed by the IIIA elements in step 2 and in steps 3 and 4 we use only three pairs of electrons for the IIIA elements. 

Theoretically, any species that contains an unshared electron pair could act as a base. In fact, most ions and molecules that contain unshared electron pairs undergo some reactions by sharing their electron pairs. Conversely, many Lewis acids contain only six electrons in the highest occupied energy level of the central element. They react by accepting a share in an additional pair of electrons. These species are said to have an open sextet. Many compounds of the Group IIIA elements are Lewis acids, as illustrated by the reaction of boron trichloride with ammonia, presented earlier. 

Corresponding to the place in the Periodic Table, in Tl-compounds the metal occurs in oxidation states + I and + III. In contrast to the other Group IIIA elements, the monovalent form is more stable than the trivalent. The chemical and physical properties of metallic thallium and thallium compounds are similar to those of adjacent elements, mainly to lead (atomic number 82). 

The compounds formed by the Group IIIA elements of the periodic table, Al, Ga and In, with the group VA elements, P, As and Sb, have the potential to be extremely important semiconductor materials. The attractiveness of Group III-V compounds as electronic materials lies in the variability of electrical properties among the different compounds and the fact that these properties are often superior to those found in Si. 

In their compounds Group IA elements are always h-1, Group IIA elements are always h-2, and Group IIIA elements are mostly always h-3. 

Boron, a group IIIA element, has only three valence electrons. In the compound boron trifluoride (BF3) these three electrons are shared with three fluorine atoms. As a result, the boron atom in BF3 has only six electrons (three bonding pairs) around it. Maximum separation of three bonding pairs occurs when they occupy the corners of an equilateral... 

Any electron-d cient atom can act as a Lewis acid. Many compounds containing group IIIA elements such as boron and aluminum are Lewis acids because group IIIA atoms have only a sextet of electrons in their outer shell. Many other compounds that have atoms with vacant orbitals also act as Lewis acids. Zinc and iron(III) halides (ferric halides) are frequently used as Lewis acids in organic reactions. 

Boron is a Group IIIA element (+3 ion), but rarely occurs as a trivalent ion in nature. Its propensity to bind with oxygen results in primarily oxide and hydroxide compounds. Boron occurs as boric acid (B(OH)3) in low pH... 

Uses. Large quantities of Sb metal have been used mainly in alloys with Pb (battery grids) and other metals. Alloys are the predominant use of antimony because its brittleness bars direct use. High purity antimony (>99.999%) has a limited but important application in the manufacture of semiconductor devices. When alloyed with elements of 13th group (IIIA), the III-V compounds are formed these have important applications as infrared devices, diodes and Hall effect devices. Also used for fireworks and thermoelectric piles. 

A large number of binary AB compounds formed by elements of groups IIIA and VA or IIA and VIA (the so-called III-V and II-VI compounds) also fcrystallize in diamond-like structures. Among the I-VII compounds, copper (I) halides and Agl crystallize in this structure. Unlike in diamond, the bonds in such binary compounds are not entirely covalent because of the difference in electronegativity between the constituent atoms. This can be understood in terms of the fractional ionic character or ionicity of bonds in these crystals. 

It can readily be shown that there is no exceptional stability (in an absolute sense) of the s electrons in the heavier elements. Table 18.3 fists the ionization energies of the valence shell s electrons of the elements of Groups IIIA (13) and IVa (14). Although the ts electrons are stabilized to the extent of -300 U mol-1 (3 cV) relative to the 5s electrons, this cannot be the only source of the inert pair effect since the 4s electrons of Ga and Ge have even greater ionization energies and these elements do not show the effect—the lower valence Gaff) and Geffl) compounds are obtained only with difficulty. 

There is also a pronounced tendency for the Group IIIA metals to form metal-metal bonds and bridged structures. The electron configuration ns2 np1 suggests the possible loss of one electron from the valence shell to leave the ns2 pair intact. The electron pair that remains in the valence shell is sometimes referred to as an inert pair, and a stable oxidation state that is less than the group number by two units is known as an inert pair effect. The fact that oxidation states of +2, +3, +4, and +5 occur for the elements in Groups IVA, VA, VIA, VIIA, respectively, shows that the effect is quite common. Thus, it will be seen that the Group IIIA metals other than aluminum have a tendency to form +1 compounds, especially thallium. 

CAS 7429-90-5. Metallic element of atomic number 13 group IIIA of the periodic table aw 26.98154 valence 3 no stable isotopes. Monovalent in high-temperature compounds (A1C1 and A1F). Most abundant metal in earth s crust third most abundant of all elements. Does not occur free in nature. 

The elements in Group IIIA form compounds, such as AICI3, that are planar and, therefore, nonpolar. What is the hybridization at the central atoms ... 

One important goal when deriving Lewis structures is to associate each atom with an octet of electrons, the same number of electrons found in the valence shells of the noble gases. In reality, only a few elements consistently achieve an exact octet of electrons in covalent compounds, but those that do are the important elements found in the first and second periods of the periodic table, most notably H, C, N, O, and F. Elements in the third and higher periods have more empty orbitals (d-orbitals) in their valence shells and can expand their capacity to accommodate as many as 10, 12, or even 14 electrons. Elements like P, S, I, and several others can form compounds like PC15, SFs, and IF7. Yet, these same elements form many compounds and ions with an octet of electrons in their valence shells. Other elements, like boron (Group IIIA), have only three valence electrons, and when all are used to form bonds, as in BF3, boron ends up with only six electrons in its valence shell. 

Amongst the hydrides of elements of Groups IIIA, IVA and VA, boron hydrides were among the earliest of inorganic compounds to be successfully gas chromatographed. 

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