. Group (Boron group) elements: . . Occurrence: The boron occurs mostly as borates and its important ores are borax - Na [B O (OH) ].8H O and kernite - Na [B O (OH) ].2H O..
Aluminium is the most abundant metal and occurs as oxides and also found in aluminosilicate rocks. Commercially it is extracted from its chief ore, bauxite (Al O .2H O). The other elements of this group occur only in trace amounts. The other elements Ga, In and Tl occur as their sulphides.
. . Physical properties: Some of the physical properties of the group elements are listed below Table . Physical properties of group elements Property Boron Aluminum Gallium Indium Thallium Physical state at K Solid Solid Solid Solid Solid Atomic Number Isotopes B Al Ga In Tl - - - - Property Boron Aluminum Gallium Indium Thallium Atomic Mass (g.mol - at K) .
Electronic configuration [He]2s 2p [Ne]3s 3p [Ar]3d 4s 4p [Kr]4d 5s 5p [Xe] 4f 5d 6s 6p Atomic radius (Å) . . . .
. Density (g.cm - at K) . . .
. . Melting point (K) . Boiling point (K) .
. Chemical properties of boron: Boron is the only nonmetal in this group and is less reactive. However, it shows reactivity at higher temperatures. Many of its compounds are electron deficient and has unusual type of covalent bonding which is due to its small size, high ionisation energy and similarity in electronegativity with carbon and hydrogen.
Formation of metal borides: Many metals except alkali metals form borides with a general formula M x B y (x ranging upto and y ranging upto or higher) Direct combination of metals with boron: Cr + nB K CrB n