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Encyclopedia of Physical Science and Technology EN011H-551 July 25, 2001 18:33

Periodic Table (Chemistry) 677

FIGURE 3 The modern long form of the periodic table. The color (shading) Scheme is discussed in Sections VI
through IX.

and oxygen (O) are the two chief components in the at- tiesinchemicalandphysicalproperties.Changesfromone
mosphere and are, of course, essential for life. Carbon element to the next are less pronounced than in the main
(C) is so ubiquitous that an entire subdiscipline, organic group elements. Included among the transition elements
chemistry, has been created to study its compounds. Sili- are the metals that are most important in construction,
con (Si) and aluminum (Al) are among the most plentiful alloying, and plating—vanadium (V), chromium (Cr),
elements in the earth’s crust. These elements are members manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), and
of a fairly large collection know as main group or rep- zinc (Zn). After the transition elements comes gallium
resentative elements. This category includes Groups 1, 2 (Ga)—the ekaaluminum of Mendeleev, right where he
(sometimes 12), and 13 through 17. They are called repre- predicted it. Five more elements, culminating in krypton
sentative because they exhibit a wide range of properties (Kr), follow. The same pattern is repeated in row 5: an
and serve as prototypes for other elements. Because of alkali metal, an alkaline earth, the 10 metals of the sec-
the uncoupling of the subgroups, the fourth and fifth peri- ond transition series, and 6 more elements in Groups 13
ods have 18 elements each. The 10 metals from scandium through 18.
(Sc) through zinc (Zn) head columns labeled 3 through Row 6 demonstrates that the long-form periodic table
12. They constitute the first transition series (though some is not enough. Element number 58, cerium (Ce), does
authors exclude the elements of Group 12 from this clas- not have sufficient chemical or physical similarity to tita-
sification and assign them to the representative elements). nium (Ti) or zirconium (Zr) to merit inclusion in Group 4.
Members of the transition series exhibit certain similari- Instead, it is much more like 14 other elements called