Sodium Through Argon
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The most commonly encountered oxidation states for the nonmetals are shown in the table below, along with examples. The highest possible positive oxidation state of an atom is the charge that it would have if it lost all of the electrons in its outer, incomplete electron shell. Thus carbon and silicon have maximum oxidation numbers of +4 because they both have four electrons to lose. Nitrogen and phosphorus have a maximum ON of +5, as in HNO3and H3PO4. Sulfur has a maximum of +6, as in H2SO4. You might expect oxygen to behave the same way, but oxygen is too small and holds its outer electrons too tightly. (Compare the first ionization energies of O and S on Page 9.) No oxygen compounds are known in which oxygen has an ON as high as +6. The size effect seen with oxygen applies even more strongly to fluorine. Chlorine in HClO4 shows an ON of +7, the expected maximum; but the smaller fluorine atom holds its electrons very tightly and has no compounds with positive oxidation states |
The lowest possible negative oxidation state of an atom is the charge that the ion would have if it picked up enough electrons to fill its outer shell completely and produce the electronic configuration of the next heavier noble gas. For F and Cl, this means a minimum ON of -1 as in HF and HCl; for O and S, -2 as in H20 and H2S; for N and P, -3 as in NH3and PH3; and for C and Si, -4 as in CH4and SiH4. The two extreme maximum and minimum values, plus ON = 0, are the most common oxidation states for the elements we have discussed so far. Intermediate states are less common and usually occur at intervals of two in ON, representing shifts of pairs of electrons. Thus sulfur has common oxidation states of -2, 0, +4, and +6; and
chlorine shows states -1, 0, +1, +3, +5, and +7. Though others to
these are possible. For example, ClO2,
where chlorine has an oxidation state of +4 can be formed, but is
not common. |
