THE TRANSITION ELEMENTS
|One property of transition metals is the formation of
highly colored ions in solution. This photo shows just a few of the
colors associated with transition metal ions.
General Introduction to the Transition Elements
The fouth row of the periodic table does not follow the
pattern set in the second and third. After the 4s orbital is filled by
the elements potassium (K) and calcium (Ca), the next electrons are placed
into the 3d orbitals. Because there are five d orbitals in a given
shell, the next block of the periodic table is ten elements wide. The ten
elements following calcium, as well as the corresponding elements in the
fifth and sixth periods, are referred to as the transition metals. The
transition elements are some of the most widely used and most common elements
on the periodic table, and include iron, copper, silver, and gold. The
physical and chemical properties of the transition elements are, in many
ways, very different from the physical and chemical properties of the alkali
and alkaline earth metals. Some of these differences are discussed in the
sections that follow.
The properties of the transition elements do not vary
greatly across a period. For example, consider the second period elements.
Sodium and magnesium have distinctive metallic properties, silicon is a
metalloid, phosphorous and sulfur are solids with nonmetallic properties,
and both chlorine and argon are gases. There is a dinstinct progression
from elements with metallic properties to elements with nonmetallic properties.
In contrast, the properties of the transition metals do not vary greatly
moving across a period. In contrast, all of the transition elements have
definite metallic properties. Consider again the second period elements.
Moving from left to right across the second period elements, there is is
a trend towards decreased atomic radius. Magnesium has a smaller
atomic radius than sodium, and aluminum has a smaller atomic radius than
magnesium. Moving left to right across the first transition series, however,
there is a general trend towards an increase in atomic radius in the first
half of the series, amd in the latter half of the series atomic radius
remains relatively constant. Other chemical properties, such as ionization
energy and electronegativity, remain relatively constant across a transition
A major difference between the transition metals and other
metals lies with the ability of the transition metals to form coordination
compounds. In these types of compounds, molecules with an unshared
electron pair, such as water or ammonia, donate the unshared pair to a
transition metal or ion. The transition metals are able to accomodate the
extra electrons by placing them into vacant d orbitals. The color of transition
metals can vary greatly depending upon the coordinated molecules. For example,
in dilute aqueous solution copper(II) is pale and nickel(II) is pale green.
When ammonia is added, the color of the copper(II) ion changes from pale
blue to a much darker blue as the coordinated water molecules are replaced
by ammonia. For nickel(II), a change from green to violet as ammonia
Most transition metal compounds are highly colored. In
contrast, compounds of the alkali metals and alkaline earth metals are
always white. The color of transition metals arises from a split in the
energies of the d orbitals caused by coordinated molecules. Oustide of
the presence of coordinated molecules, the d orbitals are degenerate,
meaning that they have the same energy. In the presence of coordinated
molecules, the degeneracy is removed. The energy difference bewteen the
orbitals happens to correspond to the energy of visible light.
Lastly, many of the transition metals exhibit multiple
oxidation states. The alkali metals and alkaline earth metals exhibit predictable
oxidation states; all of the alkali metals form +1 ions and all of the
alkaline earth metals form +2 ions. Unfortunately, there is no easy formula
for predicting the oxidation states of the transition metals. These range
from +1 all the way to +7.
Densities of the First Row Transition Elements
Units are grams per cubic centimeter
Atomic Radii of the First Row Transition Elements
Units are picometers
First Ionization Energies of the First Row Transition
Electron Configurations of the First Row Transition