chapter
17
Elements and Their Properties
3
section ●
Mixed Groups
What You’ll Learn
the differences between
metals, nonmetals, and
metalloids
■ what allotropes are
■ the different crystal
structures of carbon
■ why synthetic elements
are important
■
Before You Read
Have you ever seen a mixed-breed dog? What characteristics
of different breeds did the dog have?
Read to Learn
read the section, highlight the
name of each element group
that is discussed. Then highlight
the names and uses of some of
the elements in that group.
C Build Vocabulary
●
Make a vocabulary Foldable
like the one below to help you
understand how the elements
in the mixed groups are similar
and different.
Metalloids
Boron Group
Carbon Group
Nitrogen Group
Oxygen Group
Synthetic
Elements
306
Properties of Metalloids
Can an element be a metal and a nonmetal? In some ways,
elements called metalloids are. Metalloids share unusual
characteristics. Metalloids are elements that can form ionic
and covalent bonds with other elements and can have the
properties of metals and nonmetals. For example, some
metalloids can conduct electricity better than most nonmetals.
However, they do not conduct electricity as well as some
metals. This property gives them the name semiconductors.
Except for aluminum, the metalloids are the elements on
the periodic table that are located along the stair-step line.
Metalloids can be found in Groups 13, 14, 15, 16, and 17.
The Boron Group
The metalloid boron is the
first element in Group 13.
You might find two boron
compounds in your house.
The first is borax. Borax is
added to laundry detergents
to soften water. The other is
boric acid, an antiseptic.
Compounds called boranes
are used for jet and rocket fuel.
CHAPTER 17 Elements and Their Properties
5
B
13
Al
31
Ga
49
ln
81
Tl
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Identify Elements As you
Aluminum is a metal in Group 13. It is the most common
metal in Earth’s crust. You have seen aluminum in soft drink
cans, foil wrap, and cooking pans. Aluminum is strong and
light and is used in making airplanes.
The Carbon Group
Atoms of the elements in
Group 14 have four electrons
in their outer energy levels.
Other than this, the elements
in the carbon group are very
different. Carbon is a
nonmetal, silicon and
germanium are metalloids,
and tin and lead are metals.
6
C
14
Si
Picture This
1. Identify Circle the
metalloids in the figure.
32
Ge
50
Sn
82
Pb
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Carbon Carbon occurs as an element in coal. Compounds of
carbon make up oil and natural gas. Carbon can combine
with oxygen to produce carbon dioxide, CO2. Plants use CO2
and sunlight to make food. All organic compounds contain
carbon, but not all carbon compounds are organic.
Silicon and Germanium The metalloid silicon is the second
most common element in Earth’s crust. Most silicon is found
in sand (SiO2). It also is found in almost all rocks and soil.
Allotropes are different forms of the same element that have
different molecular structures. Molecular structure is how the
atoms in a molecule are arranged.
Silicon has two allotropes. One allotrope of silicon is a
hard, gray substance. The other is a brown powder. Because it
is a semiconductor, silicon is used in many electronic devices,
such as transistors and computer chips. A semiconductor is
an element that conducts electric current under certain
conditions. Germanium is the other metalloid in the carbon
group. It is used with silicon to make semiconductors.
Tin and Lead Tin is used to coat other metals to prevent
corrosion. It also is mixed with other metals to make bronze
and pewter. Tin cans are made of steel coated with tin. Lead is
a soft metal that was once used to make paints. Lead is no
longer used in paint because it is toxic.
2. Explain What are
semiconductors?
What are the allotropes of carbon?
What do a diamond ring and a pencil have in common? The
diamond in a ring and the graphite in a pencil are carbon. There
are three known allotropes of carbon. They are diamond,
graphite, and buckminsterfullerene (BUK mihn stur ful ur een).
Reading Essentials
307
3. Apply Why do you think
some saw blades are coated
in diamond powder?
Diamonds Diamonds are clear and extremely hard. In fact,
they are the hardest things in the world. In a diamond, each
carbon atom is bonded to four other carbon atoms. The
bonded carbon atoms form a geometric shape called a
tetrahedron. Many of these tetrahedrons join together to form
a giant molecule. In this molecule, the atoms are held tightly
together in a strong crystalline structure. This strucure is why
diamonds are so hard.
Graphite Graphite is a black powder that is made of hexagonal layers of carbon atoms. In the hexagons, each carbon
atom is bonded to three other carbon atoms. The fourth electron in each atom is bonded weakly to the layer above or
below it. These weak bonds let the layers of carbon atoms
slide easily past each other. This makes graphite very slippery.
Buckminsterfullerene Buckminsterfullerene was discovered
in the 1980s. It forms molecules that are shaped like soccer
balls. It is named after R. Buckminster Fuller, who designed
structures with similar shapes. Scientists have used
buckministerfullerene to make tiny tubes called nanotubes.
They are one-billionth of a meter in diameter. You can stack
tens of thousands of nanotubes to get the thickness of one
sheet of paper. Nanotubes might be used some day to make
smaller, faster computers.
4. Use Percentages Assume
you inhale in about 6 L of
air per minute. How much
nitrogen do you breathe in
one minute?
308
The Nitrogen Group
Group 15 is known as the
7
nitrogen family. Atoms of
N
each element in the group
15
have five electrons in their
P
outer energy levels. Group
33
15 elements usually share
As
their electrons in covalent
51
bonds with other elements.
Sb
About 80 percent of the
83
air you breathe is nitrogen.
Bi
In the air, nitrogen exists as
diatomic molecules, N2. All organisms need nitrogen
compounds to live. Even though you breathe it, your body
cannot use nitrogen in its diatomic form. It must be in the
form of a nitrogen compound. Nitrogen often is used to make
compounds called nitrates and ammonia, NH4. Nitrates are
compounds that contain the nitrate ion, NO3. Nitrates and
ammonia are important ingredients of fertilizers.
CHAPTER 17 Elements and Their Properties
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Applying Math
How are elements of the nitrogen group used?
Phosphorus is a nonmetal that has three allotropes. Its
compounds are used to make many things, including fertilizers,
water softeners, match heads, and fine china. Antimony is a
metalloid, and bismuth is a metal. These elements are added to
metals to lower their melting points. Automatic fire sprinkler
heads sometimes contain bismuth. The metal melts from the
heat of a fire and turns on the sprinkler.
The Oxygen Group
8
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Oxygen Group 16 on the
O
periodic table is the oxygen
16
group. Oxygen, a nonmetal,
S
makes up about 21 percent
34
of air. Oxygen exists in the
Se
air as a diatomic molecule,
52
O2. During electrical storms,
Te
some oxygen molecules,
84
O2, change into ozone, O3.
Po
Nearly all living things on
Earth need O2 to live. Living things also depend on a layer of
O3 in the atmosphere, called the ozone layer. The ozone layer
protects living things from the Sun’s radiation.
Picture This
5. Use a Diagram What is the
atomic number of oxygen?
Sulfur The second element in the oxygen group is sulfur. It is
a nonmetal and has several allotropes. Sulfur combines with
metals to form compounds called sulfides. Some sulfides are
colorful and are used as pigments in paints.
Other Elements Selenium, a nonmetal, and tellurium and
polonium, metalloids, are the other elements in Group 16.
You need a tiny amount of selenium in your body, so it is
included in multivitamins. But too much selenium is toxic.
Selenium also is used in photocopiers.
Synthetic Elements
Scientists have created elements that usually do not exist on
Earth. These are called synthetic elements. To create them, scientists smash existing elements with particles from a heavy ion
accelerator. Except for some isotopes of natural elements, all
synthetic elements have more than 92 protons. Many synthetic
elements disintegrate, or fall apart, soon after they are made. It
may seem strange to make elements that fall apart, or disintegrate, but scientists are learning about atoms this way.
6. Apply What happens to
many of the synthetic elements after they are made?
Reading Essentials
309
How are synthetic elements used?
Scientists smash protons into uranium to make neptunium,
element 93. In about two days, half of neptunium atoms
disintegrate. When neptunium atoms disintegrate, they form
plutonium, element 94. Plutonium has been produced in
nuclear reactors and is used in bombs. Plutonium also can be
changed to americium, element 95. You probably have some
americium in your home. There is a small amount of the
element in smoke detectors. An electric plate in smoke
detectors attracts some of the charged americium particles
and makes an electric current. A lot of smoke will break the
current and set off an alarm.
7. Infer The atomic number
of einsteinium is 99. Is einsteinium a transuranium
element? Why or why not?
8. Draw Conclusions Why do
you think scientists have
not discovered new natural
elements in many years?
310
What are transuranium elements?
Transuranium elements have more than 92 protons, the
atomic number of uranium. The transuranium elements
are located toward the
bottom of the periodic
table. Some are in the
actinide series. Others
are on the bottom row
of the main periodic
table. All of the
transuranium elements
92
are synthetic. They also
U
are unstable and many
disintegrate quickly.
Why make elements?
For centuries, scientists discovered new natural elements.
Now, all new elements are created in laboratories. When
these atoms disintegrate, they are said to be radioactive.
Radioactive elements can be useful. For example, technetium
has medical uses.
If most transuranium elements break down quickly, why
make them? Scientists make new elements to study the forces
that hold the nucleus together. In the 1960s, scientists
theorized that stable synthetic elements exist. Maybe scientists
will one day find a way to make transuranium elements that
do not break down. Perhaps a transuranium element will be
found that has everyday uses.
CHAPTER 17 Elements and Their Properties
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Picture This
After You Read
Mini Glossary
allotropes: different forms of the same element that have
different molecular structures
metalloids: elements that can form ionic and covalent bonds
with other elements and can have the properties of metals
and nonmetals
semiconductor: an element that can conduct electricity
under certain conditions
transuranium element: an element with more than 92
protons
1. Review the terms and their definitions in the Mini Glossary. Write a sentence that tells
what semiconductors are used for.
2. Use the graphic organizer below to list the properties of metalloids. Then list examples of
some important metalloids from each group.
Metalloids
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Boron Group
Carbon Group
3.
Oxygen Group
Nitrogen Group
As you read the section, you highlighted the element groups that were
discussed and the names and uses of some of the elements in each group. Was this
a good strategy for learning the information? Why or why not?
End of
Section
Reading Essentials
311