Kelter P., Mosher M., Scott A. Chemistry. The Practical Science

Подождите немного. Документ загружается.

268 Chapter 7 Periodic Properties of the Elements

Nonmetals possess characteristics that are generally quite different from those of

metals.

Nonmetals are generally

■

gases or dull, brittle solids at room temperature and pressure

■

poor conductors of electricity (with the exception of the form of carbon

known as graphite)

■

likely to form negatively charged ions when they react to form ionic com-

pounds

Despite being small in number, the nonmetals include some of the most abun-

dant elements found in living things, particularly the carbon, hydrogen, oxygen,

nitrogen, phosphorus, and sulfur atoms from which the chemicals of life are

largely made.

Between the metals and nonmetals in the periodic table we ﬁnd elements

known as

metalloids,or semimetals. Speciﬁcally, boron, silicon, germanium, ar-

senic, antimony, tellurium, and astatine make up the list of elements we call met-

alloids. These elements share some of the characteristic properties of both the

metals and nonmetals, making it difﬁcult to place them in either of these two

main categories. For example, silicon and germanium have properties of both

metals and nonmetals. Unlike the metals, these elements are not good conductors

of electricity, but unlike the nonmetals, they are not very poor conductors of elec-

tricity. Their ability to conduct electricity lies somewhere in between that of the

Selected Nonmetals, Their Sources in Nature,

and Some of Their Industrial Uses

Nonmetal Sources in Nature Industrial Uses

C Coal, graphite, diamonds Steel manufacture, pencil “lead”

Cl Salt (NaCl), briny water Water puriﬁcation, manufacture

of dyes and explosives

N Air Fertilizers, gunpowder, low-

temperature reactions, inert

atmospheres

O Air Medical ﬁeld, steel manufacture,

combustion

P Apatite (calcium hydroxy Fertilizer, chemical warfare agent,

phosphate) rat poison, steel manufacture

S Iron pyrite, galena, barite, pure Black powder, fertilizer, ﬁreworks,

element rubber production

TABLE 7.4

127.60

(210)

10.811

28.086

72.64

74.922

121.760

The metalloids.

Video Lesson: General

Properties of Nonmetals

7.3 The Next Level of Structure—Groups in the Periodic Table 269

La*

†

104

105

106

107

108

109

110

Uun

111

Uuu

IIIB

IVB

VIB

VIIB

IIB

100

101

102

103

IIA

IIIA

IVA

VIA

VIIA

VIIIA

*Lanthanide

series

†

Actinide

series

112

Uub

Period

VIIIB

810

The nonmetals, shown in green, have properties that are opposite those of the metals, shown in blue.

metals and that of the nonmetals. We say that they are semiconductors, which

makes their use as materials in the computer-manufacturing industry ideal.

The subdivision into metals, nonmetals, and metalloids is the ﬁrst level of

structure found within the periodic table. The next, and more fundamental, level

is the subdivision into the vertical columns called groups and the horizontal rows

called periods.

7.3 The Next Level of Structure—

Groups in the Periodic Table .

Elements within any of the vertical columns of the periodic table, which are

known as groups, share some signiﬁcant chemical properties. There is a clear ex-

planation for the chemical similarities of elements within each group based on

each atom’s electron arrangements. For instance, elements in any of the

main

groups

, traditionally labeled IA through VIIIA, all have the same number of elec-

trons in their outer energy level, which corresponds to the highest principal

quantum number. The outer electrons—the

valence electrons—are very signiﬁ-

cant in determining how an atom interacts with and reacts with other atoms. For

those elements known as transition elements, the deﬁnition of valence electrons

actually includes electrons in two energy levels.

Application

HEMICAL ENCOUNTERS:

Commercial Uses of

the Main-Group

Elements

6.941

22.990

39.098

85.468

132.905

(223)

270 Chapter 7 Periodic Properties of the Elements

Recent modiﬁcations to the periodic table have been made by the Interna-

tional Union of Pure and Applied Chemistry (IUPAC). One such modiﬁcation is

the standardization of the numbers at the top of each of the columns of the peri-

odic table. In this system, the columns have been numbered from 1 to 18 from left

to right. Although this numbering system has eliminated confusion based on the

number of the column, vital information about the elements in the particular

groups of the periodic table has been lost. The authors prefer the use of the his-

torically common system of numbering the groups (IA, IIA, IB, etc.). You can

compare this time-honored system to the new IUPAC numbering system in the

periodic table on the inside front cover of this text.

Group IA: Hydrogen and the Alkali Metals

The elements in Group IA, apart from hydrogen, are known as the alkali metals

because they are highly reactive elements that combine with water to form chem-

icals called alkalis. [Al qili is from the Arabic, describing the burning of the salt-

wort plant, which produces an ash that forms an alkaline (basic) solution. Alkali

metals form alkaline solutions when they react with water. We will discuss acids

and bases in Chapter 17.] The alkali metals all have one valence electron in an s

orbital, which they generally lose when reacting, to form ions with a +1 charge.

We don’t ﬁnd the alkali metals as free elements in the environment because they

are so chemically active that their atoms have all reacted to form compounds or

dissolved ions. Sodium is not found in its elemental state but, rather, in the form

of sodium ions (Na

). Sodium ions are the most abundant positive ions in sea-

water, and they are also plentiful in the internal environment of our

blood and intercellular ﬂuids.

Hydrogen shares some characteristics with the alkali metals,

particularly its tendency to react by forming a +1 ion (H

). In

other respects, however, it is quite different from the alkali metals.

It is not a metal; it can also form a negative ion, the “hydride” ion

−

), when combining with other alkali metals; and two hydrogen

atoms can combine by covalent bonding to form the hydrogen

molecule (H

The alkali metals.

Group IIA: The Alkaline Earth Metals

The elements in Group IIA are known as the alkaline earth metals. These are also

reactive metals, although generally less reactive than the alkali metals. They have

two valence electrons within an s orbital, which they generally lose when reacting,

to form ions with a +2 charge. Compounds of these metals combined with

oxygen are reasonably common in the environment. Because these metal oxides

Some Commercial Uses of Group IA Elements

Hydrogen Fertilizers, plastics, pharmaceuticals, fuel, fuel cells

Lithium Glass making, television tubes, battery electrolytes, lithium–aluminum

alloys in the aerospace industry, greases

Sodium Nuclear reactors, reagent, salt, washing soda

Potassium Fertilizers, soaps and detergents, explosives, glass and water

puriﬁcation

Rubidium Photoelectric cells

Cesium Special glass, radiation-monitoring equipment, atomic clock

Francium None (too rare)

TABLE 7.5

Video Lesson: Hydrogen, Alkali

Metals, and Alkaline Earth

Metals

Video Lesson: Hydrogen

Video Lesson: The Alkali Metals

Video Lesson: The Alkaline Earth

Metals

10.811

26.982

69.723

114.818

204.383

Group IIIA.

9.012

24.305

40.078

87.62

137.327

(226)

The alkaline earth

metals.

7.3 The Next Level of Structure—Groups in the Periodic Table

271

were so readily available in the Earth, and because they form

alkalis when dissolved in water, the elements in Group IIA were

originally given the name alkaline earth metals. For example, cal-

cium oxide (CaO) is an alkaline compound used in the manufac-

ture of cement and steel.

Group IIIA

The elements in Group IIIA are substantially less reactive metals than those in

either Group IIA or Group IA. They all have three valence electrons, two in an

s orbital and one in a p orbital. When they react to form ionic compounds, they

generally do so by losing the three outer electrons to form ions with a +3 charge.

Note that as the number of electrons that an atom loses to form an ion increases,

the reactivity of the element decreases. This is our ﬁrst example of a trend within

the periodic table—a characteristic that varies in a logical and

regular manner as we move through the table. The most signiﬁ-

cant Group IIIA element that we gather from the environment is

aluminum (23 million metric tons were produced worldwide in

2005, according to the International Aluminum Institute), found

in the ore known as bauxite, which is composed of aluminum

oxide (Al

) combined with varying amounts of water.

Some Commercial Uses of the Group IIIA Elements

Boron Glass making, soaps and detergents, nuclear

reactor control rods

Aluminum Packaging, especially soft drink containers, trans-

portation (lightweight components in motor

vehicles), window frames, aircraft parts, engines,

kegs, cooking oils, indigestion tablets

Gallium Semiconductors, microwave equipment

Indium Display devices, low-melting-point alloys and

solders, semiconductors, ﬁre sprinkler systems

Thallium Rat poisons and hair removers (now banned)

TABLE 7.7

Some Commercial Uses of Group IIA Elements

Beryllium Telecommunications equipment, automotive electronics, computers,

undersea communications equipment, pipe products in the oil and gas

industry

Magnesium Automotive industry, bicycles, luggage

Calcium Metallurgic applications, lead and aluminum industries, nuclear

applications, cement, soil conditioner, water treatment

Strontium Cathode-ray tubes, automotive industry, special glass, ﬁreworks, ﬂares

Barium Given to patients with digestive disorders to highlight the bowels in

an X-ray, drilling ﬂuid, oil for gas wells

Radium Cancer treatment, luminous paint for watches and clocks

TABLE 7.6

A conveyor belt at the Rio do Norte mining company in the

Amazon forest in Brazil piles up bauxite ore, a source of alu-

minum oxide. Mining bauxite can be very devastating to the

environment, but the Rio do Norte mining company has

been successful in reforesting the land that they’ve mined,

as evidenced by the green area in the middle of the photo.

Their efforts challenge the notion that the Amazon forest

must be destroyed to tap its riches and offer an opportunity

to learn how to repair degraded forests.

Video Lesson: Aluminum

Video Lesson: CIA

Demonstration: The Reaction

between Al and Br

12.011

28.086

72.64

118.710

207.2

Group IVA.

272 Chapter 7 Periodic Properties of the Elements

Group IVA

The elements in Group IVA, with four valence electrons, two in an s orbital and

two in individual p orbitals, occupy the “center ground” of the main-group ele-

ments, and they include elements of central importance to living things and the

fabricated materials with which modern society survives. Carbon, at the top of

the group, can be regarded as the basic elemental “building block”of life, because

the chemicals of life are largely based on chemical chains and rings of carbon

atoms with various other atoms attached. Carbon does not generally form ions.

Instead, it forms covalent bonds (we will discuss these in Chapter 8), in which

electrons are more or less shared between two atoms. Group IVA also includes sil-

icon, the basis of the “silicon chips” of the computer industry, and the semicon-

ductor germanium, also used in the manufacture of computer chips.

Group VA

The elements in Group VA have ﬁve valence electrons, two sharing an s orbital

and three occupying individual p orbitals. When they form ions, these elements

generally gain three electrons to form ions with a −3 charge. The Group VA ele-

ments also readily participate in covalent bonding. Nitrogen, for example, makes

up 80% of the volume of the Earth’s atmosphere in the form of N

molecules.

Nitrogen is also a crucial component of many covalently bonded compounds

required for life, such as DNA, proteins, and many vitamins and hormones. Phos-

phorus is also crucial for life, being one of the atoms found in DNA, for example,

and being part of the compounds found in fertilizers that are used to grow the

food we consume.

Some Commercial Uses of the Group IVA Elements

Carbon Commercial and military aircraft, ﬁbers, thermoplastic

matrix materials, petrochemicals, clothing, dyes,

fertilizers, fuels, pharmaceuticals

Silicon Aluminum alloys, silicones, silicon chips used in

computers, semiprecious stones

Germanium Semiconductors, transistors,

catalysts (substances that

greatly increase the rate of a reaction without being con-

sumed) in polymer production, glass for infrared devices

Tin Coatings for other metals, bronze, soft solder, pewter,

special paint used on boats to prevent barnacles

Lead Storage batteries, cable covering, radiation shielding, pipes,

pewter, pottery, additive in gasoline, lead crystal glass

TABLE 7.8

14.007

30.974

74.922

121.760

208.980

Group VA.

Some Commercial Uses of the Group VA Elements

Nitrogen Fertilizers, plastics, explosives, dyes

Phosphorus Fertilizers, matches, detergents, coating to prevent

corrosion

Arsenic Pesticides, wood preservatives, semiconductors,

special glass

Antimony Flame retardants, pigments, lubricants, ammunition,

used to harden other metals

Bismuth Industrial and laboratory chemicals, pharmaceuticals,

cosmetics, replacement for lead in steel alloys and alu-

minum in ceramics, high-temperature superconductors,

indigestion tablets

TABLE 7.9

Video Lesson: General

Properties of Carbon

Video Lesson: Silicon

Video Lesson: Nitrogen

Video Lesson: Phosphorus

7.3 The Next Level of Structure—Groups in the Periodic Table 273

Group VIA: The Chalcogens

The elements in Group VIA are known as the chalcogens, a name derived from

the Greek khalkos (“copper”), because the copper ores contain the elements in

this group. All of the elements in Group VIA have six valence electrons, two in an

s orbital and four distributed within three p orbitals. When they form ions, the

Group VIA elements gain two electrons to form ions with a −2 charge.

In looking for Group VIA elements of signiﬁcance to ourselves and the envi-

ronment, we immediately turn to oxygen. Oxygen gas, in the form of O

mole-

cules, makes up about 21% of the atmosphere and is the gas we must breathe in

order to stay alive. We need it because it combines with hemoglobin, as we noted

in the chapter opening, and reacts with food molecules to release the energy that

powers all life. We have also met, in Chapter 2, the relatively rare form of oxygen

known as ozone (O

) that is a vital part of our environment high in the atmos-

phere, where the ozone layer absorbs harmful UV rays, but is a troublesome

environmental pollutant at ground level.

Group VIA also contains sulfur, another element that is both vital for life and

associated with harmful pollution. We need the sulfur that is a part of proteins

and some vitamins and other important biochemicals, as well as fertilizers and

industrial chemicals such as sulfuric acid (H

), but oxides of sulfur such as

sulfur dioxide (SO

) are pollutants that can cause “acid rain.”

15.999

32.065

78.96

127.60

(209)

The chalcogens.

Application

Some Commercial Uses of the Group VIA Elements

Oxygen Steel making, metal cutting, chemical industry

Sulfur Lead–acid storage batteries, fertilizers, water treatment,

petroleum reﬁning, drying agents

Selenium Photoreceptors, glass colorant, pigments, metallurgic

and biological applications, photoelectric cells, photo-

copiers, semiconductors

Tellurium Additive in steel and other metal alloys, catalyst in syn-

thetic rubber production

Polonium Source of alpha radiation, heat source in space vehicles

TABLE 7.10

Sulfur can be found near volcanoes as

yellow rocks.

Video Lesson: Oxygen

Video Lesson: Sulfur

4.003

20.180

39.948

83.798

131.293

(222)

The noble gases.

274 Chapter 7 Periodic Properties of the Elements

Group VIIA: The Halogens

The elements in Group VIIA are known as the halogens (from the Greek hals +

gen, meaning “salt makers”) because they are reactive nonmetals that can com-

bine with metal ions to form the chemicals we call salts. All of the elements in

Group VIIA have seven valence electrons, two in an s orbital and ﬁve distributed

among three p orbitals. When they form ions, as happens when they become part

of salts, they gain one electron per atom to form ions with a −1 charge. The most

common example of a salt is sodium chloride (NaCl), which we know as

common table salt, and we will meet many other examples throughout this book.

Chloride ions (Cl

−

) are abundant in seawater and in the blood and intercellular

ﬂuids of the body. Tiny amounts of ﬂuoride ions (F

−

) are important in making

our teeth resistant to decay.

Group VIIIA: The Noble Gases

The elements of Group VIIIA are all largely unreactive gases, and the group is col-

lectively known as the

noble gases, in the sense of aloof nobility—being distin-

guished from the other, much more reactive elements. The noble gases, which are

also known as the

inert gases, are present in very small amounts in the environ-

ment, but through their remarkable stability, they reveal to us one of the most sig-

niﬁcant secrets of chemistry. All the noble gases apart from helium have eight

valence electrons distributed between a full s orbital and three full p orbitals. The

18.998

35.453

79.904

126.904

(210)

The halogens.

Some Commercial Uses of the Group VIIA Elements

Fluorine Welding metals, frosting glass, used in the nuclear

power industry, insulating gas for high-power electric-

ity transformers, as an additive to municipal water

supplies

Chlorine Chemical warfare, bleach, PVC plastic, water

puriﬁcation

Bromine Flame retardants, pharmaceutical intermediates,

swimming pool disinfectants, industrial water

treatment, air conditioning absorption systems, pre-

cious metal leaching, fuels, additives, insecticides,

photography

Iodine Conductive polymers, fuel cells, dyes, photography,

pharmaceuticals, industrial catalyst

Astatine Nuclear reactors

TABLE 7.11

Some Commercial Uses of the Group VIIIA Elements

Helium Used by divers to dilute the oxygen they breathe, bal-

loons, low-temperature research

Neon Filling discharge tubes, ornamental lighting

Argon Filling discharge tubes, provide an inert atmosphere for

high-temperature metallurgic processes, light bulbs

Krypton High-quality light bulbs

Xenon Research purposes

Radon Gives off alpha particle radiation

TABLE 7.12

Video Lesson: Halogens

Video Lesson: Aqueous Halogen

Compounds

Video Lesson: Properties

of Noble Gases

fact that atoms of these elements do not naturally react either with themselves or

with any other elements (although some compounds of xenon, krypton, and

radon have been made under extreme conditions) indicates that they have an ex-

ceptionally stable valence electron arrangement. This arrangement is known as a

stable

octet because it contains eight valence electrons. Helium, with only two va-

lence electrons, also has an exceptionally stable electron arrangement because it

has a completely full energy level. It is the “odd one out” among the noble gases

in that, with only two electrons, it does not have a stable octet but nevertheless

shares the remarkable stability of the other inert gases. When we examine chem-

ical bonding in more detail in Chapter 8, we will ﬁnd that many chemical reac-

tions can be understood in terms of the participating atoms acquiring electron

arrangements that are similar to the stable valence electron arrangements of the

noble gases.

Although they are very rare, we have found various good uses for the noble

gases of the environment. Helium, for example, is well known as the “lighter than

air” gas within party balloons, weather balloons, and airships that allows them to

rise upward. Neon has found fame as the gas within “neon” lights. In light bulbs,

argon, mixtures of argon and nitrogen, or, in newer “halogen” bulbs, krypton and

xenon are used as inert gases to prevent the tungsten ﬁlament from oxidizing, and

xenon has similar uses in ﬂash photography.

EXERCISE 7.3 Group Fun

How many electrons are found in the valence shell of each of these elements?

a. Be b. As c. I d. In

Solution

a. Two, both in the 2s orbital

b. Five, two in the 4s orbital and three in the 4p orbitals

c. Seven, two in the 5s orbital and ﬁve in the 5p orbitals

d. Three, two in the 5s orbital and one in the 5p orbitals

PRACTICE 7.3

Indicate which element is described by each of these phrases.

a. Two valence electrons, both in the 6s orbital

b. One valence electron, in the 3s orbital

c. Six valence electrons, two of them in the 2s orbital

d. Four valence electrons, and the element is a nonmetal

See Problems 23 and 24.

The Transition Elements

In the middle of the periodic table we ﬁnd elements known as the transition ele-

ments

, with the inner transition elements usually shown as a separate block, as in

Figure 7.1. The transition elements are arranged in short groups, historically la-

beled IB through VIIIB in the case of the main transition elements, and currently

unlabeled for the inner transition elements.

The elements in the ﬁrst period of the inner transition elements are known as

the

lanthanides, and the second period forms the actinides. These inner transition

elements are shown separately, primarily for the visual ease of having the periodic

table ﬁt into a convenient space. A more logical version of the periodic table is

shown in Figure 7.5, with the inner transition elements ﬁtted where they belong

Uses of the

noble gases.

7.3 The Next Level of Structure—Groups in the Periodic Table

275

Video Lesson: Transition Metals

and Nonmetals

Video Lesson: Properties of

Transition Metals

Video Lesson: CIA

Demonstration: Copper

One-Pot Reactions

in terms of their atomic numbers. The inner transition elements make up the

f-block, and they have some speciﬁc chemical characteristics due to electrons in

f orbitals acting as valence electrons in addition to those in the outer s orbital. We

most often think of the inner transition elements such as uranium and pluto-

nium in terms of their nuclear rather than their chemical properties.

The transition elements of the d-block have electrons in d orbitals that can

count as valence electrons, in addition to the electrons in the s orbital of their

highest energy level. This situation of having valence electrons in two energy

276 Chapter 7 Periodic Properties of the Elements

IIA IIIA IVA

VIA VIIA

VIII

Period

FIGURE 7.5

Periodic table with the lanthanides and actinides where they belong in terms of electron arrangement.

Transition metals, such as the copper

atom (green), are an essential part of

some enzymes. This three-dimensional

model is spinach plastocyanin, an

enzyme involved in energy production

in some plants. The hydrogen atoms

have been omitted from the model to

make it easier to see the other atoms.

140.116

232.038

140.908

231.036

144.24

238.029

(145)

(237)

150.36

(244)

151.964

(243)

157.25

(247)

158.925

(247)

162.500

(251)

164.930

(252)

167.259

100

(257)

168.934

101

(258)

173.04

102

(259)

174.967

103

(262)

The f-block elements.

7.3 The Next Level of Structure—Groups in the Periodic Table 277

levels arises because the energies of the electrons involved are very close. It results

in some interesting and important chemical characteristics, such as the ability to

readily form ions with different values of charge.

The special chemistry of the transition elements, such as iron, cobalt, copper,

and zinc, makes many of them vital for life. Biochemists, for example, have

become quite used to the idea that when a difﬁcult feat of chemistry is achieved

within a living thing, it is very often catalyzed by an enzyme (a biological sub-

stance that signiﬁcantly increases the rate of a process; see Chapter 22) that in-

cludes a transition metal ion at the “active site,” where the chemical reaction

occurs. Transition elements are also widely used as catalysts in the chemical in-

dustry and, in the automotive industry, as rhodium- and platinum-based cat-

alytic converters in cars.

The Elements of Life

Figure 7.6 shows the periodic table with all of the elements that make up the

human body highlighted in color and their relative abundances indicated, and

Table 7.13 lists the relative abundance of these elements within us. Note the loca-

tion of these elements in the periodic table. Can you suggest any generalizations

about their locations? Can you offer any explanations for your suggestions?

The two most clear-cut generalizations are that the human body is largely

constituted of elements only from the upper right-hand portion of the periodic

table and that the noble gases are not part of the chemistry of life.

La*

†

104

105

106

107

108

109

110

Uun

111

Uuu

IIIB

IVB

VIB

VIIB

IIB

100

101

102

103

IIA

IIIA

IVA

VIA

VIIA

VIIIA

Principle components

Major minerals

Trace minerals

*Lanthanides

†

Actinides

112

Uub

Period

VIIIB

810

Application

HEMICAL

ENCOUNTERS:

The Elements

of Life

FIGURE 7.6

The elements that make up you.