Atom is electrically a neutral particle. The total negative charge of its electrons rotating around a kernel is counterbalanced with a total positive charge of the protons which are in a kernel. In interaction with other atom the particle can lose the electrons or attract strangers. The negatively charged or positively charged ion is formed. The size and the sign of a charge, corresponding to quantity of the accepted or given electrons, characterizes element atom oxidation level.
1. Oxidation levels of atoms can be positive, negative or zero (when molecules of substance consist of uniform atoms). Very important condition: total oxidation level of a molecule is always equal to zero.
2. It is also necessary to know that element atom oxidation level size not always coincides with its valency. The good example of that is carbon. You can make sure, having remembered formulas of some organic molecules, at it at the identical valency equal to four, there can be different oxidation levels.
3. Metals at connection with nonmetals always have positive oxidation levels. Nonmetals, respectively, negative. If connection consists of atoms of different nonmetals, then more electronegative (that is having negative oxidation level) will be that element which is located in Mendeleyev's table above and more to the right. Its highest negative oxidation level can be found, having subtracted from figure 8 number of group in which it is. The second element, respectively, will have the positive oxidation level equal to number already of its group.
4. For example, N2O5 nitrogen oxide. Find oxidation levels of the elements which are its part, being guided by these rules. Both nitrogen, and oxygen – nonmetals. What of these elements more electronegative? According to Mendeleyev's table it is oxygen as it is located flush with nitrogen, but more to the right (in the sixth group, and nitrogen – in the fifth). Means, its oxidation level is negative and equal to-2. Nitrogen oxidation level, thus, is positive and equal to +5. Check whether this molecule is neutral (taking into account indexes). Total charge of atoms of nitrogen +10. A total charge of atoms of oxygen – 10. The condition is met.