Metals tend to react with nonmetals to form ionic compounds.
RULES FOR WRITING FORMULAS FOR IONIC COMPOUNDS:
The positive ion is always written first in the formula.
The ratio of positive ions to negative ions must be such that the total number of positive charges equals the total number of negative charges; the formula unit must be electrically neutral.
The smallest set of subscripts that give electrical neutrality is always chosen. We always write empirical formulas for ionic compounds.
Methods of preparation and characterization of catalysts. The -Al2O3 was prepared by precipitation of Al(OH)3 from an AlCl3 1M solution by an NH3 1M solution. The precipitate was washed for removing NH4+ and Cl- repetitively until they could not be detected, left at a temperature of 40oC for 5h to remove free H2O and then calcined at 600oC for 8 h. The -Al2O3+ MgO (1% w/w) was prepared by coprecipitation of Al(OH)3 and Mg(OH)2 from a mixture of AlCl3 1M and MgCl2 1 M solutions at appropriate proportion by Nh3 1M followed by the same remaining procedure. After calcining. the materials were grinded, sieved and the particle size fraction 25-75 m was obtained. Oxides were characterized by dissolving an amount of doped one in HCl solution which was analysed by the atomic absorption technique to determine its true composition and by XRD and BET. Cylindrical pressed powder tablets, 10 mm in diameter and 1.6 mm thick, were examined by impedance spectroscopy to examine the conductive behaviour of aluminas.