Complex connections are the chemicals of complex structure consisting of the central atom – a kompleksoobrazovatel and also the internal and external sphere. The internal sphere consists of the neutral molecules or ions which are strongly connected with a kompleksoobrazovatel. Such molecules are called ligands. The external sphere can consist of anions or cations. In any difficult connection the elements which are its part have the oxidation level.
Instruction
1. Take for an example the substance which is formed at reaction of gold with "royal vodka" – mix of three parts of the concentrated salt acids and one part of the concentrated nitric acid. Reaction proceeds according to the scheme: Au + 4HCl + HNO3 = H [Au(Cl)4] + NO + 2H2O.
2. Complex connection – hydrogen tetrachloraurate is as a result formed. Kompleksoobrazovatel in him is the gold ion, ligands – chlorine ions, the external sphere – a hydrogen ion. How to determine oxidation levels of elements in this complex connection?
3. First of all define what of the elements which are a part of a molecule, the most electronegative that is who will draw to himself the general electronic density. It is, certainly, chlorine as it is located in the top right part of the table of Mendeleyev, and on electronegativity concedes only to fluorine and oxygen. Therefore, its oxidation level will be with the sign "minus". And what size of oxidation level of chlorine?
4. Chlorine, as well as all other halogens, is located in the 7th group of the table of Mendeleyev, at his external electronic level there are 7 electrons. Having drawn one more electron on this level, it will pass into a steady position. Thus, its oxidation level will be equal to-1. And as in this complex connection four ions of chlorine, a total charge will equal-4.
5. But the sum of sizes of oxidation levels of the elements which are a part of a molecule has to be equal to zero, any molecule electrically is neutral. Thus, the negative charge-4 has to be counterbalanced by a positive charge +4, at the expense of hydrogen and gold.
6. As hydrogen is the very first element of the table of Mendeleyev and can give only one electron for formation of a chemical bond, its oxidation level is equal to +1. Respectively, in order that the total charge of a molecule was equal to zero, the ion of gold has to have oxidation level +3. The task is solved.