Untitled - Kelly Walsh High School

Chemistry of the Elements 285
Be Careful!
gases do not form anions and this method leaves them with a zero oxidation
number. The next column to the left, the halogens, is 1; then comes 2, followed
by 3, and finally 4. (Remember these are oxidation numbers; you
should not expect to obtain isolated ions such as C 4 .) In compounds, fluorine
has only a 1 oxidation number. The anionic charge determined by this procedure
is the lowest possible oxidation number for the nonmetal.
Even though fluorine only exists in compounds in the 1 oxidation state, it, like
all elements, has a zero oxidation state in the elemental form. This means that
fluorine is 1 in CaF 2, PbF 2, SF 4, and ClF 3, and 0 in F 2.
All nonmetals except fluorine and the lighter noble gases (He, Ne, and Ar) can
form compounds where the nonmetal has a positive oxidation number. A nonmetal
can only adopt a positive oxidation number if there is a more electronegative
nonmetal present. The maximum oxidation number of a nonmetal is related
to the position of the nonmetal on the periodic table. Using the older system
(Roman numerals), the maximum oxidation is equal to the Roman numeral for
the column. Using the newer system, the maximum is the group number 10.
Xenon exhibits the highest observed oxidation number for a nonmetal. Xenon
is 8 in XeO 4.
A nonmetal may adopt any oxidation number between the values predicted in
the preceding two paragraphs. The only exceptions are fluorine, which is only
1 in compounds, and helium, neon, and argon, which have no known compounds.
When there is a choice of oxidation states, there must be additional
information available in order to allow you to choose the correct state.
19-6 Periodic Trends of Nonmetals
Nonmetals follow the general trends of atomic radii, ionization energy, and
electron affinity. Radii increase to the left in any row and down any column on
the periodic table. Ionization energies and electron affinities increase up any
column and towards the right in any row on the periodic table. The noble gases
do not have electron affinity values. Ionization energies are not very important for
the nonmetals because they normally form anions. Variations appear whenever
the nonmetal has a half-filled or filled subshell of electrons. The electronegativity