The Group 3A Elements

The Group 3A elements (valence electron configuration nsznp1) generally show the increase in metallic character in going down the group that is characteristic of the representative elements. Some physical properties, sources, and methods of preparation for the Group 3A elements are summarized in Table 18.9. 

TABLE 18.9 Selected Physical Properties, Sources, and Methods of Preparation for the Group 3A Elements 

Boron 20 798 — Kernite, a form of borax (Na2B407 4H20) Reduction by Mg or H2 

Aluminum 50 581 -1.66 Bauxite (Al203) Electrolysis of A1203 in molten Na3AlF6 

Gallium 62 577 -0.53 Traces in various minerals Reduction with H2 or electrolysis 

Aluminum, the most abundant metal on earth, has metallic physical properties, such as high thermal and electrical conductivities and a lustrous appearance however, its bonds to nonmetals are significantly covalent. This covalency is responsible for the amphoteric 

Boron is a typical nonmetal, and most of its compounds are covalent. The most interesting compounds of boron are the covalent hydrides called boranes. We might expect BH3 to be the simplest hydride, since boron has three valence electrons to share with three hydrogen atoms. However, this compound is unstable, and the simplest known member of the series is diborane (B2H6), with the structure shown in Fig. 20.7(a). hi this 

Element Radius ofM + (pm) Ionization Energy (kj/mol) °(V)for M +H-3e Source Method of Preparation 

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Comparing the data in Tables 6.14 and 6.15 shows that dihydrogen bonding to the same proton donor depends strongly on the natme of the group 3A elements The interaction energy increases in the order... 

The valence electron configuration of the group 3A elements is ns2 npl, and their primary oxidation state is +3. In addition, the heavier elements exhibit a +1 state, which is uncommon for gallium and indium but is the most stable oxidation state for thallium. 

The group 3A elements—B, Al, Ga, In, and T1—are metals except for boron, which is a semimetal. Boron is a semiconductor and forms molecular compounds. Boranes, such as diborane (B2H6), are electron-deficient molecules that contain three-center, two-electron bonds (B-H-B). 

What is the most common oxidation state for each of the group 3A elements ... 

What is the oxidation state of the group 3A element in each of the following compounds ... 

Table 18.10 summarizes some important reactions of the Group 3A elements. 

The Group 2A Elements The Group 3A Elements The Group 4A Elements The Group 5A Elements The Chemistry of Nitrogen... 

What is the valence electron configuration for the Group 3A elements How does metallic character change as one goes down this group How are boron and aluminum different Predict the formulas of the compounds formed when aluminum reacts with F2, O2, S, and N2. 

Figure 8.16 The Group 3A elements. The low melting point of gallium (29,8 °C) causes It to melt when held In hand.

We see that BF3 and other similar molecules have a central element that does not satisfy the octet rale. Boron shares only six electrons (as do most of the Group 3A elements). 

Theoretically, any species that contains a lone pair of electrons could act as a base. In fact, most ions and molecules that contain unshared electron pairs undergo some reactions by sharing their electron pairs with atoms or molecules that have low-energy vacant orbitals. 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 from a Lewis base. Many compounds of the Group 3A elements are Lewis acids, as illustrated by the reaction of boron trichloride with ammonia, presented earlier. 

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