Name CuBr2, SCl2 & BaF2. Explain the use or omission of the Roman numeral (II) & the prefix di-.

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ncchemist | eNotes Employee

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We are to name CuBr2, SCl2, and BaF2.

CuBr2 can be identified by two different names.  The compound contains the transition metal copper (Cu).  Many transition metal elements can form 2 different cations, so you must distinguish between the two of them.  You can do this either with Roman numerals or with the suffixes "ous" and "ic".  Copper can form either the +1 or +2 cation.  Since we know that bromide must be -1, then the copper in CuBr2 must be +2.  That means we can either name it copper (II) bromide or cupric bromide.  The Roman numeral denotes the exact charge of the copper, and the suffix "ic" denotes that it is the larger of the two possible charges for copper.  You do not usually use prefixes like "di" with transition metal compounds since the Roman numeral designations are standard.

SCl2 would most commonly be called sulfur dichloride.  We use the prefix "di" in this case since sulfur can adopt different oxidation states and we need to show that there are only two chlorides.  You could call the compound sulfur (II) chloride to denote that the sulfur is in the +2 oxidation state since the chlorides always have a -1 charge.  But you would never use both the Roman numeral and the "di" prefix (sulfur (II) dichloride) since that is showing the same information twice.

BaF2 is called barium fluoride.  We do not need either Roman numerals or the "di" prefix in this case since barium can only form the +2 cation (it is a group 2 element) and fluorine can only form the -1 anion (it is a halogen).  So the name barium fluoride is used since there is no other possible combination of barium and fluoride.

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