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In general the magnitude and sign of the oxidation state of atoms are
determined by comparing the electronegativity of the elements that are a part of the
compound. A more electronegative atom has a negative oxidation state, and an
atom with a lower electronegativity has a positive oxidation state. Since the
electronegativity values of the simple substances atoms are the same, the their
oxidation states in this case are zero ( , , , ) . The oxidation state of
ions in ionic compounds are equal to the magnitudes of their charges. For
2-
2-
–
–
example, ions of Ca , Ba have an oxidation state of +2, and for Cl and F ions
the oxidation state is -1.
Let us consider some features of determining the oxidation state of atoms in
molecules using the example of Nitrogen compounds: NН 3, NО 2, НNO 2, КNО 3. In
the ammonia Nitrogen as an atom with a higher electronegativity (χ = 3.0) in
comparison with the Hydrogen atom (χ = 2.1) has a negative oxidation state -3
(NH 3). In the nitrogen (IV) NO 2 oxide the oxygen atom will be more
electronegative (χ = 3.5), so the Nitrogen atom in this case has a positive oxidation
state +4. In НNО 2 and КNO 3, the oxidation state of Nitrogen is determined
according to the fact that the oxidation states of the atoms of Hydrogen and
Potassium are +1, and Oxygen is -2. Knowing that the sum of the oxidation states
of all atoms in a molecule should be zero, we find out that in НNО 2, КNО 3 the
oxidation state of Nitrogen are +3 and +5, respectively.
In general, the oxidation state of atoms in compounds can be positive
( , , , negative ( , ) or equal
to zero ( , ), ). In some compounds, the oxidation state may
take fractional values ( , ) .
The maximum positive oxidation state of atoms corresponds to the number of the
group of the periodic system. The only exception is the elements of the subgroup
of the first group (Cu, Ag, Au), where the oxidation state +2 and +3 is larger than
the group number, as well as the metals of the eighth group (Fe, Co, Ni, Rh, Pd, Ir,
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