FORMATION OF AL2CL6 MOLECULE, molecular mass of anhydrous aluminum chloride, SIGMA BOND,COVALENT BONDING IN TERMS OF ORBITAL OVERLAPPING

 FORMATION OF AL₂CL₆ MOLECULE:

             The relative molecular mass of anhydrous aluminum chloride in benzene solution is found to be 267. The fact that anhydrous aluminum chloride get dissolve in benzene (organic solvent) shows that the chloride is covalent bonded. The expected formula for aluminum chloride is ALlCl₃ and its relative molecular mass should be 133.5 but the observed relative molecular mass of the chloride in benzene solution is twice than expected value i.e; 267.       This fact shows that aluminum chloride dimerises in the solution to form (AlCL₃)₂ i.e; Al₂Cl₆.

             The dimerisation is possible because the aluminum atom in each AlCl₃ is electron deficient have accept lone-pair of electron from bounded chlorine atom of another adjacent AlCL₃. Thus Al₂Cl₆ is formed due to formation of two dative covalent bonds.

             Al2 Cl₆

            27x2+35.5x6

            54+213

            = 267

 COVALENT BONDING IN TERMS OF ORBITAL OVERLAPPING:

             In a covalent molecule bonded electrons are present in molecular orbitals rather than atomic orbitals. The molecular orbitals are formed due to overlapping of atomic orbitals.. There are two types of molecular orbitals depending upon the nature of overlapping i.e; sigma (a) bond and pi ( ) bond.

SIGMA BOND:

             A single covalent bond consists of a orbital and is often called a bond. The covalent bond in which bonding molecular orbital is symmetrical atoms a line joining the two atomic orbital or covalent bond which is formed due to head to head overlap of two atomic orbitals is called sigma (a) bond. Electron density in sigma bond is concentrated between the two bonded nuclear.