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Is there any rule why a crystal made of Si and C is named silicon carbide SiC, but never carbon silicate CSi? Both silicon and carbon are in the same group, so share many of the atomic properties, so why the asymmetry in naming? Are all such compounds named like <HigherPeriod> <LowerPeriod>?

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As per the rules of inorganic chemistry nomenclature the element of the compound which is more electronegative is to be written at the end of molecular formula and its name is to be written after all the elements which have lower electronegativity are written hence the given compound is pronounced as silicon-carbide and not carbon-silicide

a more detailed view about electronegativity of elements can be found in this picture

enter image description here

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  • $\begingroup$ Aha, so solutions like $\text{Ga}_x\text{In}_{1-x}\text{P}$ should be written with $\text{Ga}$ first, then $\text{In}$, or does this rule only work for the last element (here $\text{P}$)? $\endgroup$ – Ruslan Jul 3 '14 at 15:33
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    $\begingroup$ @Rusian As a general rule, it is assumed that electronegativity in main groups grows from left to right and from down to up in s-p blocks. It is extremely debatable in many cases, which element is more electronegative if we move on diagonal from left-up to down-right, say, chlorine in many cases is capable to oxidize chlorine and vice versa. As for numeric electronegativity scales, there are several and none is ... undebatably right. $\endgroup$ – permeakra Jul 3 '14 at 15:39
  • $\begingroup$ @Ruslan i think permeakra cleared your doubt if you want any more explanation feel free to comment $\endgroup$ – agha rehan abbas Jul 3 '14 at 15:51
  • $\begingroup$ Not quite. My comment asked if all elements preceding the most electronegative should also be sorted with increasing electronegativity. And permeakra just said about how electronegativity behaves across periodic table. $\endgroup$ – Ruslan Jul 3 '14 at 16:06
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    $\begingroup$ Here's a great answer related to exactly how electronegativity considerations enter IUPAC nomenclature. $\endgroup$ – Nicolau Saker Neto Jul 4 '14 at 0:30
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Silicates are salts of silicic acids, $\ce{xH2O * ySiO2}$ and $\ce{SiC}$ is not one. The proper term is silicide. It is usually assumed, that s/p element upper or righter from considered one is more electronegative, and "-ide" nomenclature assumes that second element has negative charge and is more electronegative. Of course, there are exceptions. For example, $\ce{RhB}$ is still written as is, despite $\ce{Rh}$ having higher electronegativity.

However, the ordering of elements in formulas and naming of compounds are subjects of tradition. For example, despite having higher negativity, nitrogen in the formula of ammonia precedes hydrogen: $\ce{NH_3}$, while for water hydrogen precedes oxygen $\ce{H2O}$, and both may be called 'hydrides' in some cases. It may be viewed as another rule: in case of a isolated particle central atom of the molecule first, substituents later (composite substituents written in curly braces), but acidic hydrogens first. In brutto-formula indexes symbols of elements AFAIK are ordered alphabetically except that carbon and hydrogen are first two.

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  • $\begingroup$ You must have meant "hydrogen follows nitrogen" not "nitrogen follows nitrogen". $\endgroup$ – Ruslan Jul 3 '14 at 18:21
  • $\begingroup$ @Rusian yes, indeed. Corrected $\endgroup$ – permeakra Jul 3 '14 at 18:33
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why a crystal made of Si and C is named silicon carbide SiC, but never carbon silicate

To add to agha rehan abbas' and permeakra's comments, the "ate" suffix typically implies the presence of oxygen (carbonate, silicate, phosphate, etc.). Since $\ce{SiC}$ does not contain oxygen, you would not use the "ate" suffix in this case.

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    $\begingroup$ Yeah, I guessed I was wrong here after reading agha's "and not carbon-silicide". $\endgroup$ – Ruslan Jul 3 '14 at 16:07

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