Since the oxidation number of Chromium is +3, and the oxidation number of Silicon is -4. Why is the chemical formula for Chromium III Silicide Cr3Si2?

Can somebody please explain to me please???????THANKS A LOT!!!

The best answer I can give is that although the oxidation number for Cr is +3 in most of its compounds and the oxidation number for Si, in most of its compounds is (I think +4 in SiO2, SiCl4, etc), the oxidation number for Si is not +4 (or -4) in Cr3Si2. In Cr3Si2, if we call Cr +3, then each Si is -4.5.

Oxidation numbers are nothing more than a set of man-made rules and is really a book keeping procedure to keep up with loss and gain of electrons. Let me show you what I mean.
CN^- ==> CNO^-
Suppose we call C+4, then N is -5 on the left and on the right it is (+4C, -2 for O, so N is -3) So the N atom changed from -5 to -3 which is a loss of 2 electrons . But suppose I'm on a test and forgot the rules. Simple. I make up my own.
Let's call C+19. then
CN^- gives C +19 and N must be -20.
In CNO^-, C is +19, O is -2, so N must be -18. The nitrogen atom changed from -20 to -18 which is a loss of 2 electrons.

Sure! I'd be happy to explain.

In order to determine the chemical formula for Chromium III Silicide (Cr3Si2), we need to consider the oxidation numbers of chromium and silicon.

The oxidation number represents the charge that an atom would have if all of its bonds were 100% ionic. In compounds, the sum of the oxidation numbers of all atoms must equal zero. In the case of Cr3Si2, we have three chromium atoms and two silicon atoms.

We know that the oxidation number of chromium is +3. Since there are three chromium atoms, the total oxidation number contributed by chromium in Cr3Si2 is 3 * (+3) = +9.

Now, we need to figure out the oxidation number of silicon in order to balance out the total oxidation number. Since the overall compound is electrically neutral, the sum of the oxidation numbers must equal zero.

Since we have two silicon atoms in the compound, and the total oxidation number is +9, the oxidation number of silicon must be -4. In other words, each silicon atom contributes -4 to the total.

Therefore, the chemical formula Cr3Si2 is used to balance out the oxidation numbers. The three chromium atoms contribute a total of +9, while the two silicon atoms contribute a total of -8 (-4 * 2 = -8). This balances out to zero, making the compound electrically neutral.

So to summarize: the chemical formula Cr3Si2 is used because it balances out the oxidation numbers, with three chromium atoms contributing +9 and two silicon atoms contributing -8, resulting in a total oxidation number of zero.