Chemical properties of elements vary with according to the oxidation number. Oxidation number can be positive or negative of atoms.
If an atom removes electrons completely or partially, it is defined as oxidation. When an atom looses its electrons, it is oxidized and oxidation number will be positive. Metals prefer to remove electrons. Therefore oxidation number of metals are always positive.
If an atom takes electrons completely or partially towards itself is called as reduction. When an atom gains electrons, it is reduced and oxidation number will be negative.
Note that, oxidation and reduction reactions should occur at same time. Only oxidation or reduction cannot be occurred alone.
The number of electrons taken (completely or partially) from outside or number of electrons removed (completely or partially) is defined as oxidation number.
If one electron is removed, oxidation number is +1
If two electrons are removed, oxidation number is +2.
If one electron is taken, oxidation number is -1
If two electrons are taken, oxidation number is -2.
Atoms attract electrons in the bonds. But some atoms (F, O, N, Cl) can attract electrons more than others. Electronegativity values tells us about those attraction ability of atoms. Here are some examples.
Electronegativity values of O and H are 3.5 and 2.1 respectively. Oxygen's electronegativity is much larger than H. Therefore electrons in the O-H bond are attracted towards O atom.
So, Hydrogen partially looses its electron. Therefore H gets +1 oxidation state.
Oxygen partially takes the electron of H. Therefore O gets -1 oxidation state from that part. Also O has taken an electron from outside because of that O gets another -1 oxidation value. So complete oxidation number ox oxygen is -2.
Ionization energy decreases along a group. It means removing/eliminating an electron gets easier along a group. When
eliminating an electron gets easier, ability of being oxidized increases. Otherwise we can say, reducing characteristics
increase along a group.
Ex: reducing characteristic of K is higher than Na.
Ionization energy increases along a period (left to right), therefore removing/eliminating an electron is getting hard. So oxidizing ability decreases, but reducing ability increases. Otherwise we can say, oxidizing characteristic increases along a period (left to right).
Related Tutorials to Oxidizing - Reducing Characteristics