Page 242 - 9780077418427.pdf

/Users/user-f465/Desktop
tiL12214_ch08_203-228.indd Page 219 9/1/10 9:45 PM user-f465
tiL12214_ch08_203-228.indd Page 219 9/1/10 9:45 PM user-f465 /Users/user-f465/Desktop

A Closer Look

The Rare Earths

ompounds of the rare earths were first rows contain two series of elements that actu- lasers. Samarium, ytterbium, and terbium
Cidentified when they were isolated from ally belong in periods 6 and 7, but they are have special magnetic properties that have
uncommon minerals in the late 1700s. The moved below so that the entire table is not made possible new electric motor designs,
elements are very reactive and have similar so wide. Together, the two series are called magnetic-optical devices in computers, and
chemical properties, so they were not recog- the inner transition elements. The top series is the creation of a ceramic superconductor.
nized as elements until some 50 years later. 14 elements wide from elements 58 through Other rare earth metals are being researched
Thus, they were first recognized as earths, 71. Since this series belongs next to element for use in possible high- temperature super-
that is, nonmetal substances, when in fact 57, lanthanum, it is sometimes called the conductivity materials. Many rare earths are
they are metallic elements. They were also lanthanide series. This series is also known as used in metal alloys; for example, an alloy
considered to be rare since, at that time, they the rare earths. The second series of 14 ele- of cerium is used to make heat- resistant
were known to occur only in uncommon ments is called the actinide series. These are jet engine parts. Erbium is used in high-
minerals. Today, these metallic elements are mostly the artificially prepared elements that performance metal alloys. Dysprosium and
known to be more abundant in the earth do not occur naturally. holmium have neutron-absorbing proper-
than gold, silver, mercury, or tungsten. The You may never have heard of the rare ties and are used in control rods to control
rarest of the rare earths, thulium, is twice as earth elements, but they are key materials in nuclear fission. Europium is known because
abundant as silver. The rare earth elements many advanced or high-technology prod- of its role in making the red color of color
are neither rare nor earths, and they are ucts. Lanthanum, for example, gives glass television screens. The rare earths are rela-
important materials in glass, electronic, and special refractive properties and is used in tively abundant metallic elements that play
metallurgical industries. optic fibers and expensive camera lenses. a key role in many common and high-
You can identify the rare earths in the Samarium, neodymium, and dysprosium technology applications. They may also play
two lowest rows of the periodic table. These are used to manufacture crystals used in a key role in super conductivity research.

1 Metals 2
H He
Nonmetals
3 4 5 6 7 8 9 10
Li Be B C N O F Ne
Semiconductors
11 12 13 14 15 16 17 18
Na Mg Al Si P S Cl Ar
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
87 88 89 104 105 106 107 108 109 110 111 112 113 114 115 116 118
Fr Ra Ac Rf Db Sg Bh Hs Mt Ds

FIGURE 8.19 The location of metals, nonmetals, and semiconductors in the periodic table.

an ion, since it has three protons (3+) and two electrons (2–), for
outer orbital. For several reasons, you know that strontium
a net charge of 1+. A lithium ion thus has a 1+ charge.
is a metal: (1) An atom of strontium has two electrons in
its outer orbital and atoms with one, two, or three outer
CONCEPTS Applied electrons are identified as metals; (2) strontium is located in
the IIA family, the alkaline earth metals; and (3) strontium is
located on the left side of the periodic table and, in general,
Metals and Charge
elements located in the left two-thirds of the table are metals.
Is strontium a metal, nonmetal, or semiconductor? What is Elements with one, two, or three outer electrons tend
the charge on a strontium ion? to lose electrons to form positive ions. Since strontium has
The list of elements inside the back cover of this book an atomic number of 38, you know that it has thirty-eight
identifies the symbol for strontium as Sr (atomic number protons (38+) and thirty-eight electrons (38–). When it
38). In the periodic table, Sr is located in family IIA, which loses its two outer orbital electrons, it has 38+ and 36– for
means that an atom of strontium has two electrons in its a charge of 2+.

8-17 CHAPTER 8 Atoms and Periodic Properties 219