PLEASE help me with chemistry!!?

Question

Indicated the coordination number of the metal and the oxidtion number of the metal in each of the following complexes:
Na2[CdCl4]
K2[MoOCl4]
[Co(NH3)4Cl2]Cl
[Ni(CN)5]-3
K3[V(C2O4)3]
[Zn(en)2]Br2

thanks so much!!

Answer 1

The sum of all oxidation numbers in a compound MUST equal zero.

When trying to find the oxidation number of transition metals, "go with what you know." What I mean by this is, the elements that are in Groups I, 2, and 13-18 all have pretty stable oxidation numbers. Apply the oxidation number to these elements FIRST and then the transition metal will be whatever you need to make the overall sum of the oxidation numbers zero.

For example:

In Na2(CdCl4), Na has an oxidation number of 1+ and Chlorine has an oxidation number of 1-.

In this formula you have 2 sodiums and 4 chlorines. You also have a polyatomic ion (CdCl4). In order for this formula to equal zero when you sum the oxidation numbers, the polyatomic ion must have an overall charge of 2- in order to balance out the Na2 which is a total of 2+ (1+ charge x 2). For the polyatomic ion to have an overall 2- charge, let x = the oxidation number of Cd and add the oxidation number sum for the Cl4 (this would be a 4-). So x + (- 4) = -2
Solving for x, x would have to be 2+.

To check to see if you are right, there should be a table in the back of your chemistry book which lists all the possible oxidation numbers for your transition elements. If your answer is amongst them, and your sum of oxidation numbers equal zero, then you have applied the correct charge to your transition element.

The best way to identify whether or not your compound contains polyatomic ions is this:

All compounds are composed of a positive part (written first in the formula) and a negative part (written last in the formula). If your compound contains more than 2 different elements overall, then at least one polyatomic ion is present. If the first part of the compound is NH3 [NH3 is the only positive polyatomic ion], then NH3 is the positive part of the compound (a polyatomic ion) and the remainder is the negative part of the compound. If the remainder is only one element, then it is a negative ion. If the reaminder contains more than one type of element, then you have a SECOND polyatomic ion.

If the first part of your formula is anything other than NH3, then this is a single ion and the remainder is a single ion if there is only one type of element, or a polyatomic ion if there are more than one kind of elements present.

I hope this will assist you in answering these questions. If you would like me to verify your answers once you are done, email me your answers and repeat the question in your email so I will have the formulas and I will get back to you and let you know if you are correct and if not, will try to steer you in the right direction. If I do all these for you then you will not be able to do them later on a test. (If you are only looking for "answers" and not assistance in understanding, I apologize for wasting your time.

CHEMISTRY TEACHER

Answer 2

Rather than grind through these, remember your rules for oxidation numbers. Coodination number refers to the oxidation number of the transition metal ion WITHIN the complex. So in the first example, the coordination number is 4 (4 Cl- x 1). The oxidation number of cadmium is 2, sodium = 1 each, chlorine = -1 each.

From a practical viewpoint, oxidation numbers of metals in complexes is a waste of time, but don't tell your teacher that.