2007-07-15 18:30:04 · 7 answers · asked by Anonymous in Science & Mathematics ➔ Chemistry
Man, I took chemistry a long time ago, but I'll give it a go. I think it's because Copper varies in valance. Since Cl is -1, then Cl2 is -2. And because we aren't sure what the exact valance is for Cu, then we put Copper(II) Chloride to make it a stable compound. We know that Mg is +2 so it's okay to leave MgCl2 as it is without the roman numerals.
2007-07-15 18:36:47 · answer #1 · answered by teknique 6 · 1⤊ 1⤋
Magnesium only forms the +2 cation. Therefore, if you write magnesium chloride, it is understood to be MgCl2. Copper can form both the +1 and +2 ions. Therefore, if you say copper chloride, it can mean both CuCl and CuCl2. To avoid this ambiguity, the copper is marked with its valency in Roman numerals.
2016-05-18 23:19:27 · answer #2 · answered by ? 3 · 0⤊ 0⤋
The naming system used is based on how the elements are bonded.Since the bond between magnesium and chlorine is ionic, the name is magnesium chloride. On the other hand, CuCl2 has a covalent bond and therefore follows the other naming system. Also, copper could form other molecules with chlorine such as CuCl3 and it would be called Copper (III) chloride. Since the bond between Chlorine and magnesium is ionic, there is only one molecule made.
2007-07-15 18:39:21 · answer #3 · answered by Danman 1 · 0⤊ 2⤋
Magnesium,Calcium,Aluminium,Carbon,Hydrgen,Gold Silver,Platiunum are also like that among other elements.
Copper can have a charge of +1 or +2. The ones above including Magnesium have only 1 charge.
2007-07-15 18:49:53 · answer #4 · answered by sandwreckoner 4 · 3⤊ 0⤋
Copper forms compound with a +1 valance and a +2 valance. The Roman numeral indicates which valance copper takes for the specified compound. In older practice, the terms cuprous and cupric were used for the (I) and (II) valances. Mg compounds are all with the +2 valance, so the alternate designation is not needed.
2007-07-15 18:34:47 · answer #5 · answered by cattbarf 7 · 4⤊ 1⤋
Mg can only have valence 2 so there is no doubt on the component, but Cu can have valence I or II (1 or 2). So, you must give the symbol I or II
2007-07-15 19:08:15 · answer #6 · answered by maussy 7 · 3⤊ 0⤋
Copper,like iron, is assigned more than one valence number.Thus, when writing formulas you must specify which number you're using. Most elements have one valence number.
2007-07-19 15:45:06 · answer #7 · answered by vera h 3 · 0⤊ 0⤋