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Im having a hard time calculating the oxidation number of metals as im not quite sure what the charges of d-block metals are and anything I have tried to look up says the charges can vary. So how do I figure out the oxidation number?
This time the internet is right, the oxidation number of a transition metal can vary and there are not really any hard rules that can be used like knowing that the halogens for -1 ions. To find the oxidation number of a transition metal you need to know two things, 1) the overall charge on the complex, and 2) the charge of all the ligands. The overall charge of the complex will be given, and the total charge of the transition metal and the ligands will add up to the overall charge on the complex. For knowing the charge on the ligands it is helpful to remember the charge of the common polyatomic ions, as they are also common ligands. However, if you are given a ligand that you do not recognize bound to a metal you can still determine the ligands charge. To do this you need to know what is directly attached to the atom on the ligand that is bound to the metal. For example if the ligand is NH3 I know that the N will be bound to 3 Hs and to the metal. To determine the ligands charge you next want to break the ligand-metal bond and give those 2 electrons both to the atom that was just bound to the metal, so in the NH3 example my NH3 would now have a lone pair on the N that came from the metal-N bond. Now, you determine the formal charge on the atom that was just attached to the metal, so for NH3 the N has 3 bonds and a lone pair of electrons so it will have a formal charge of 5-(2+3)=0 so I now know my ligand is neutral and any charge on my metal is going to be equal to the charge on the complex.
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