halogens are very high, and they are particularly reactive toward alkali metals and alkaline earths,
which “want” to donate electrons to the halogens to form stable ionic crystals.
NOBLE GASES
The noble gases, also called the inert gases, are found in Group VIII. They are fairly nonreactive
because they have a complete valence shell, which is an energetically favored arrangement. They
thus have high ionization energies. They possess low boiling points and are all gases at room
temperature.
TRANSITION ELEMENTS
The transition elements are those that are found between the alkaline earth metals and those with
valence p electrons (the last six columns). The numbering of the groups can get rather confusing
because of the existence of two conventions, but you needn’t be too concerned with this. These
elements are metals and hence are also known as transition metals. They are very hard and have
high melting and boiling points. As one moves across a period, the five d orbitals become
progressively more filled. The d electrons are held only loosely by the nucleus and are relatively
mobile, contributing to the malleability and high electrical conductivity of these elements.
Chemically, transition elements have low ionization energies and may exist in a variety of positively
charged forms or oxidation states. This is because transition elements are capable of losing various
numbers of electrons from the s and d orbitals of their valence shell. For instance, copper (Cu) can
exist in either the +1 or the +2 oxidation state, and manganese (Mn) occurs in the +2, +3, +4, +6, or +7
state. Because of this ability to attain positive oxidation states, transition metals form many
different ionic and partially ionic compounds. The dissolved ions can form complex ions either with
molecules of water (hydration complexes) or with nonmetals, forming highly colored solutions and
compounds, such as CuSO 4 · 5H 2 O.
Complexes of transition metal ions, called coordination complexes, are an interesting class of
species because many of them possess bright colors. This results from the fact that the formation of
complexes causes the d orbitals (normally all of the same energy) to be split into two energy
sublevels. Many of the complexes can thus absorb certain frequencies of light—those containing the
precise amount of energy required to raise electrons from the lower to the higher d sublevel. The
frequencies not absorbed give the complexes their characteristic colors.