Ionic structures and bonding
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1) Why would you expect Al2O3 to melt at such high temperatures? Predict the properties of Al2O3.
2) Why will table salt in water conduct electricity while sugar in water will not? 260308
Corrie writes .....
1. Being composed of a metal and a non-metal, one might expect aluminium oxide to be a typical ionic compound, like NaCl. The melting points of solids are determined by the type of attraction (bonding) between the particles and the strength of that attraction. Consider what the particles would be if aluminium oxide was purely ionic and the likely strength of the attraction between them, given their charges (and sizes).
If aluminium oxide was a typical ionic compound, the other properties that would follow, in addition to a high melting point, would, like NaCl, be hardness, conductivity (molten or dissolved - see below) and solubility. A chemical property would be whether the oxide was basic, acidic or amphoteric. What would you expect for aluminium oxide as a typical metal oxide? Think of a few other common metal oxides.
2. For solutions to conduct, they must contain ions that can move, to the + and - electrodes. Water itself cannot conduct because it consists of neutral molecules. To answer your question, consider what particles sodium chloride and sugar respectively are made up of, and what will be present in solution when they dissolve.
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updated: 26 March 2008
