Aluminum covalent radius

G for gallium. These values (see also in the next section) are consistent with the unpaired electron residing in a Ti-orbital. The stability of these compounds was attributed to the large size and electronic properties of the Si(f-Bu)3 substituents [26-28]. Computational data for the aluminum compound indicate an Al—Al distance of 2.537 A and a wide Al—Al-Si angle of 174.90° [26]. The longer distance for the aluminum species is a result of the larger covalent radius for this metal [18]. 

Hightened reactivity of functional groups (e.g. Cl, Br, OH, OR, OCOR, NH2, SH) at the atoms of silicon, aluminum, titanium, phoshorus and other elements in comparison with their reactivity binded with oxygen. This is due to the fact that the silicon atom is one and a half times bigger than the carbon atom it has a covalent radius of 0.117 nm, whereas the radius of the carbon atom is only 0.077 nm. It follows that functional groups of the Si atom are much more distanced from each other than... 

In this compound, too, the intemuclear distances indicate that bonding between the metal atoms is important The Al-Al distance is only 0.10 A more than the value calculated for a single bond by doubling the tetrahedral covalent radius, and 0.24 A less than the Al—Al distance in the metal The Al—Cb bonds on the other hand are 0.18 A longer than the Al—Cj bonds. The latter are equal to the Al—C single-bond value 1.96 A, calculated from the tetrahedral covalent radii of carbon and aluminum and the revised Schomaker-Stevenson mle. 

Figure 8.8 Defining metallic and covalent radii. A, The metallic radius is one-half the distance between nuclei of adjacent atoms in a crystal of the element, as shown here for aluminum. B, The covalent radius is one-half the distance between bonded nuclei in a molecule of the element, as shown here for chlorine. In effect, it is one-half the bond length.

Boron trichloride, a colorless, reactive gas of BC13 molecules, behaves chemically like BF3. However, the trichloride of aluminum, which is in the same group as boron, forms dimers, linked pairs of molecules. Aluminum chloride is a volatile white solid that vaporizes at 180°C to a gas of Al2Cl6 molecules. These molecules survive in the gas up to about 200°C and only then fall apart into A1C13 molecules. The Al,CI6 molecule exists because a Cl atom in one AlCI, molecule uses one of its lone pairs to form a coordinate covalent bond to the Al atom in a neighboring AICI molecule (33). This arrangement can occur in aluminum chloride hut not boron trichloride because the atomic radius of Al is bigger than that of B. 

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