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TABLE 8.5
number of 14. The square with the symbol Si and the
Electron structures of the noble gas family atomic number 14 is located in the third period (third row)
and in the column identified as IVA (14).
Number of Electrons in
Electron Main Energy Level Now, can you identify the period and family of the
Element Configuration 1st 2nd 3rd 4th 5th 6th 7th element iron (Fe)? Compare your answer with a classmate’s
to check.
2
Helium (He) 1s 2 — — — — — —
2
6
Neon (Ne) [He] 2s 2p 2 8 — — — — —
6
2
Argon (Ar) [Ne] 3s 3p 2 8 8 — — — — 8.6 METALS, NONMETALS,
10
6
2
Krypton (Kr) [Ar] 4s 3d 4p 2 8 18 8 — — —
AND SEMICONDUCTORS
6
2
10
Xenon (Xe) [Kr] 5s 4d 5p 2 8 18 18 8 — —
2
6
14
10
Radon (Rn) [Xe] 6s 4f 5d 6p 2 8 18 32 18 8 — As indicated earlier, chemical behavior is mostly concerned with
the outer orbital electrons. The outer orbital electrons, that is, the
highest energy level electrons, are conveniently represented with
an electron dot notation, made by writing the chemical symbol
As shown in Table 8.5, the elements in group VIIIA have with dots around it indicating the number of outer orbital elec-
orbitals that are filled to capacity. These elements are color less, trons. Electron dot notations are shown for the representative
odorless gases that almost never react with other ele ments to elements in Figure 8.18. All the group IA elements (alkali metals)
form compounds. Sometimes they are called the noble gases have one dot, all the IIA elements have two dots, and so on. This
because they are chemically inert, perhaps indicating they are pattern will explain the difference between metals, nonmetals,
above the other elements. They have also been called the rare and a third group of in-between elements called semiconduc-
gases because of their scarcity and inert gases because they are tors. (For a discussion of how to place the dots, see the chapter 8
mostly chemically inert, not forming compounds. The noble resources on www.mhhe.com/tillery.)
gases are inert because they have filled outer electron configu- One way to group substances is according to the physi-
rations, a particularly stable condition. cal properties of metals and nonmetals—luster, conductiv-
Each period begins with a single electron in a new orbital. ity, malleability, and ductility. Metals and nonmetals also have
Second, each period ends with the filling of an orbital, complet- certain chemical properties that are related to their positions in
ing the maximum number of electrons that can occupy that the periodic table. Figure 8.19 shows where the metals, non-
main energy level. Since the first A family is identified as IA, metals, and semiconductors are located. Note that about 80 per-
this means that all the atoms of elements in this family have cent of all the elements are metals.
one electron in their outer orbitals. All the atoms of elements in The noble gases have completely filled outer orbitals in their
family IIA have two electrons in their outer orbitals. This pat- highest energy levels, and this is a particularly stable arrangement.
tern continues on to family VIIIA, in which all the atoms of ele- Other elements react chemically, either gaining or losing electrons
ments have eight electrons in their outer orbitals except helium. to attain a filled outermost energy level as in the noble gases. When
Thus, the number identifying the A families also identifies the an atom loses or gains electrons, it acquires an unbalanced elec-
number of electrons in the outer orbitals, with the exception of tron charge and is called an ion. An atom of lithium, for example,
helium. Helium is nonetheless similar to the other elements in has three protons (plus charges) and three electrons (negative
this family, since all have filled outer orbitals. The electron the- charges). If it loses the outermost electron, it now has an outer
ory of chemical bonding, which is discussed in chapter 9, states filled orbital structure like helium, a noble gas. It is also now
that only the electrons in the outermost orbitals of an atom are
involved in chemical reactions. Thus, the outer orbital electrons
are mostly responsible for the chemical properties of an element.
Since the members of a family all have similar outer configura-
tions, you would expect them to have similar chemical behav-
iors, and they do.

CONCEPTS Applied

Periodic Practice

Identify the period and family of the element silicon.
Write your answer before you read the solution in the next
paragraph.
According to the list of elements on the inside back
cover of this text, silicon has the symbol Si and an atomic
FIGURE 8.18 Electron dot notation for the representative
elements.

218 CHAPTER 8 Atoms and Periodic Properties 8-16