Untitled - Kelly Walsh High School

284 CHEMISTRY FOR THE UTTERLY CONFUSED
orbitals merge to produce a valence band. In metals, the valence band is also
the conduction band. Any partially filled band is a conduction band, providing
a pathway for electron flow. This band is full for the nonmetals. A filled band
cannot conduct electricity. The metalloids have a filled valence band and, at a
slightly higher energy, an empty conduction band. The separation between
these two bands is the band gap. A relatively small input of energy can move
electrons from the filled valence band to the empty conduction band. When
electrons enter the conduction band, it becomes partially filled, and electrical
conductivity is possible.
19-4 Periodic Trends in Metallic
Properties
Metals 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. Electron affinities are
not very important for the metals because they normally form cations.
Variations appear whenever the metal has a half-filled or filled subshell of electrons.
The electronegativity values for the representative metals increase
towards the top of any column and towards the right on the periodic table. For
the transition metals, the electronegativity peaks at gold.
The metallic properties increase down any column and towards the left in any
row on the periodic table. One important metallic property is that metal oxides
are base anhydrides. A base anhydride will produce a base in water. These are
not oxidation-reduction reactions. Many metal oxides are too insoluble for
them to produce any significant amount of base. However, most metal oxides,
even those that are not soluble in water, will behave as bases to acids. A few
metal oxides, and their hydroxides, are amphoteric. Amphoteric means they
may behave either as a base or as an acid. Amphoterism is important for aluminum,
beryllium, and zinc. Complications occur whenever the oxidation number
of the metal exceeds 4 as in the oxides that tend to be acidic.
19-5 General Properties of Nonmetals
In a compound containing a metal and a nonmetal, the nonmetal is an anion.
The anionic charge of a nonmetal is predictable from the position of the nonmetal
on the periodic table. You begin on the far right and count towards the
left until you get to the column containing the nonmetal of interest. The noble