The Foundations of Chemistry

configurations of elements in the A groups are entirely predictable from their positions

in the periodic table. We also noted, however, that some irregularities occur within the B

groups.

Now we classify the elements according to their electron configurations, which is a

very useful system.

Noble Gases.For many years the Group VIIIA elements—the noble gases—were called

inert gases because no chemical reactions were known for them. We now know that the

heavier members do form compounds, mostly with fluorine and oxygen. Except for helium,

each of these elements has eight electrons in its outermost occupied shell. Their outer

shell may be represented as having the electron configuration... ns^2 np^6.

Representative Elements.The A group elements in the periodic table are called repre-

sentative elements. Their “last” electron is assigned to an outer shell sor porbital. These

elements show distinct and fairly regular variations in their properties with changes in

atomic number.

d-Transition Elements.Elements in the B groups in the periodic table are known as the

d-transition elements or, more simply, as transition elements or transition metals. The

elements of four transition series are all metals and are characterized by electrons being

assigned to dorbitals. Stated differently, the d-transition elements contain electrons in

both the nsand (n
1)dorbitals, but not in the nporbitals. The first transition series, Sc

through Zn, has electrons in the 4sand 3dorbitals, but not in the 4porbitals. They are

referred to as

First transition series: 21 Sc through 30 Zn

Second transition series: 39 Y through 48 Cd

Third transition series: 57 La and 72 Hf through 80 Hg

Fourth transition series: 89 Ac and 104 Rf through element 112

The properties of elements are
correlated with their positions in
the periodic table. Chemists use the
periodic table as an invaluable guide
in their search for new, useful
materials. A barium sodium niobate
crystal can convert infrared laser
light into visible green light. This
harmonic generation or “frequency
doubling” is very important in
chemical research using lasers and in
the telecommunications industry.

236 CHAPTER 6: Chemical Periodicity

[He] 1 s^2

Some transition metals (left to right): Ti, V, Cr, Mn, Fe, Co, Ni, Cu.