Doing a first year chem class.
Just read through the molecular naming of compounds and now I'm confused as to why $\ce{CaCl2}$ is called calcium chloride and not calcium dichloride?
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4 Answers
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The current version of Nomenclature of Inorganic Chemistry – IUPAC Recommendations 2005 (Red Book) reads as follows:
(…)
The stoichiometric name of the compound is then formed by combining the name of the electropositive constituent, cited first, with that of the electronegative constituent, both suitably qualified by any necessary multiplicative prefixes (‘mono’, ‘di’, ‘tri’, ‘tetra’, ‘penta’, etc., …). The multiplicative prefixes precede the names they multiply, and are joined directly to them without spaces or hyphens. (…)
So far, the systematic name of $\ce{CaCl2}$ should be calcium dichloride.
However,
Multiplicative prefixes need not be used in binary names if there is no ambiguity about the stoichiometry of the compound (…).
Therefore, the customary name calcium chloride is correct.
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Elements from the first 2 columns only have 1 oxidation state, so any compound they form, it is easy to determine the number of anions.
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2$\begingroup$ Apparently, calcium monochloride is a thing, albeit unstable. Barium monochloride is even used in fireworks. $\endgroup$ Mar 14, 2017 at 13:41
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Some names are just used out of habit. "Calcium chloride" has been the common name for so long, that it has simply become common usage. According to this Wikipedia article, calcium dichloride is an acceptable "other" name for the compound.
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Calcium chloride is an ionic compound so cation is named first followed by anion. Do not get confused with carbon dioxide and sulfur dioxide. They are not ionic compounds.
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6$\begingroup$ You cannot go by whether a compound is ionic or covalent to determine if the number of anions should be in the name. Aluminum chloride ($\ce{AlCl3}$) is a covalent compound. $\endgroup$– LDC3Jul 6, 2014 at 16:54