| main | contacts | site map | guest book |
7. OXIDATION LEVELS OF CHEMICAL ELEMENTS.
We already know about existence of the loaded particles ions. Positive charge of ion is equal to number of the electrons given by one atom of element; the negative charge of ion is equal to number of the electrons accepted by one atom of element. The records Na+, Ca2+, Al3 + mean that atoms of these elements have lost respectively 1, 2, 3 е-, and the records F-, O2-, N3-mean that atoms of these elements have got respectively 1, 2, and 3e-.
Oxidation levels of elements. For definition of structure of molecular connections (SO2, NH3, CO2, etc.) and ionic simple connections (Na2O, Na2SO4, etc.). At assessment of oxidation level of elements of connection represent split on one-atomic ions.
Extent of oxidation is the conditional charge of atoms of chemical element in connection calculated from the assumption that connections consist only of ions.
Oxidation levels can have positive, negative or zero value, and the sign is put before chislom:-1,-2, +3, in difference from ion charge where the sign is put after number.
The algebraic sum of oxidation levels of elements taking into account number of their atoms is equal in molecules to 0.
Oxidation levels of metals in connections always positive, the highest oxidation level corresponds to number of group of periodic system where there is this element (excepting some elementy:zoloto of Au+3 (the I group), Cu+2 (II), from the VIII group +8 only Os osmium and Ru ruthenium can have oxidation level.
Degrees of nonmetals can be both positive and negative, depending on that to what atom it is connected: if with metal atom that always negative, if with nonmetal maybe +, and - (you learn about it when studying number of elektrootritsatelnost). The highest negative oxidation state of nonmetals can be found, having subtracted from the 8th number of group in which there is this element, the highest positive it is equal to number of electrons on external layer (the number of electrons corresponds to number of group).
Oxidation levels of simple substances are equal 0 irrespective of metal it or nonmetal.
When determining oxidation levels it is necessary to use the following rules:
2. All metals have polozhzhitelny oxidation level;
3. Boron and silicon in connections have positive oxidation states;
4. Hydrogen has in connections oxidation level (+1). Excepting hydrides (compounds of hydrogen with metals of the main subgroup of the first or second of groups, the oxidation level-1, for example Na+H-);
5. Oxygen has oxidation level (-2), except for compound of oxygen with O+2F-2 fluorine and in peroxides (H2O2 - the oxidation level of oxygen (-1);
6. Fluorine has oxidation level (-1)I will provide the table where constant degrees for the most often used elements are specified:
Oxidation levels Elements +1 Li, Na, K, Rb, Cs, Ag, H (except hydrides) +2 Be, Mg, Ca, Sr, Zn, Cd, Ba +3 Al, B - 1 F, { Cl, Br I-if are connected to hydrogen or metals } - 2 O, { S, Se, in connections with hydrogen and metals } - 3 { N, P, As } - in connections with hydrogen and metals Order of determination of oxidation levels in connections.
At two chemical elements of potassium and oxygen of oxidation level respectively +1 and-2 are constant and equal. Number of oxidation levels at oxygen it is equal (-2)·7=(-14), at potassium (+1)·2=(+2). The number of positive oxidation states is equal to number of negative. Therefore (-14)+ (+2)= (-12). The number of positive degrees equally 12 means at chrome atom, but atoms 2, means it is the share of one atom (+12):2=(+6), we write down degrees окисленя over elements K +2Cr+62O-27Types of profile for production of warehouse racks. | computer house tables