I had a hard time in chem class cuz i don't know when to put the roman numerals if the ionic compound needed it.
Wed, 2011-09-28 04:12
Most elements only have ONE valency number (Look up writing formula in the tutorial section). If you were asked to name NaCl you would say sodium chloride; MgCl2 = magnesium chloride; AlCl3 = aluminium chloride. No Roman numbers as the elements have their expected valency numbers (1 for group1, 2 for group2 etc).
If you were asked to name CuCl you might say copper chloride. However in this copper (a transition element which can have more than one valency number) has the same valency as Cl (group 7 and valency =1). So more correctly, the name is copper(I) chloride, while CuCl2, which is also copper chloride has copper with twice the valency of Cl. So copper's valency =2 and name is correctly Copper(II) chloride
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