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

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258 Chapter 6 Quantum Chemistry: The Strange World of Atoms

108. Iridium (element 77) is one of the metals that can be found

in the Earth’s crust not combined with other elements. It

is a brittle, lustrous metal and has a melting point over

2400

a. Judging on the basis of iridium’s position in the periodic

table, what other elements would it most resemble?

b. Does iridium have any unpaired electrons?

c. Using the Aufbau principle, determine to what sublevel

the 25th electron was added to the conﬁguration of

iridium.

Comprehensive Problems

109. a. The light produced in the explosion of a dramatic ﬁre-

works display reaches you before the sound of the explo-

sion. Use another reference to determine the speed of

sound. Then determine the ratio of the speed of light to

the speed of sound.

b. What is the speed of light in miles per hour?

110. When you observe the striking colors of the ﬁreworks at

a special occasion, you are observing emission spectra.

Describe, chemically, what has transpired in the atoms of

the elements to cause the emission of light.

111. What is the longest wavelength of the Lyman series of the

hydrogen emission spectrum?

112. Explain how both the volume and the energy of an electron

associated with an atom are quantized.

113. Using the equation that allows calculation of the radii of

energy levels for single-electron situations in hydrogen,

compare the distance between the ﬁrst and second energy

levels to the distance between the third and fourth

energy levels and to the distance between the ﬁfth and sixth

energy levels.What trend do you notice?

114. The equations used by Bohr are valid for the hydrogen

atom, but when they are applied to helium, a signiﬁcant

error shows up. And when they are applied to lithium and

elements with higher atomic numbers, the error becomes so

large that the equations offer little. However, the equations

can be applied to helium and lithium ions with a fair agree-

ment with experimental values. What helium and lithium

ions would be most like the hydrogen atom?

115. When applying wave properties to electrons in atoms, we

use the expression 2πr = nλ. Explain why n can have only

integer values.

116. Deﬁne the terms discrete and continuous. List ﬁve everyday

items that have some property that is discrete and ﬁve

that have a property that is continuous on a macroscopic

scale.

117. Assign possible quantum numbers for each of these orbital

pictures. Assume that each orbital is in the lowest possible

principal shell.

a. b. c.

118. Compare the ground-state electron conﬁgurations of

potassium and argon. Explain why it is easier to remove the

outer electron of potassium than that of argon, even though

potassium has more positive charge in its nucleus.

119. A 385 nm photon of light strikes a sheet of a particular

metal and ejects an electron at a velocity of 6.1  10

m/s.

What is the energy, in kJ/mol, associated with this photon?

120. A 0.30 L cup of water is placed in a microwave and irradi-

ated with microwaves of 12.0 cm wavelength. The tempera-

ture of the water raises from 25°C to 80°C. How many

photons are used to heat the water?

121. a. What is the frequency and energy associated with a

photon of light from a ruby laser (see Table 6.4)?

b. What mass, in ounces, would a particle exhibiting that

wavelength have if it were traveling at half the speed of

the photon?

Thinking Beyond the Calculation

122. A photon with wavelength λ = 2165 nm strikes an excited

hydrogen atom.

a. What energy, in joules, is associated with this photon?

What energy, in joules, is associated with a mole of these

photons?

b. What is the frequency of the photon?

c. Which region of the electromagnetic spectrum contains

photons of this energy?

d. If the photon is absorbed by the hydrogen atom, to what

energy level is the electron promoted? To make the

calculation easier, assume that the electron begins in the

n = 4 energy level.

e. If the hydrogen atom relaxes back to the n = 2 energy

level from the n =7 level, what would be the wavelength

of the photon that was emitted? Which region of the

spectrum contains this photon?

f. What could you write as the electron conﬁguration for

the hydrogen atom described in part e, after emission of

the photon?

yyy

zz z

259

Contents and Selected Applications

7.1 The Big Picture—Building the Periodic Table

7.2 The First Level of Structure—Metals, Nonmetals,

and Metalloids

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

Chemical Encounters: Commercial Uses of the Main-Group Elements

Chemical Encounters: The Elements of Life

7.4 The Concept of Periodicity

7.5 Atomic Size

7.6 Ionization Energies

7.7 Electron Afﬁnity

7.8 Electronegativity

7.9 Reactivity

7.10 The Elements and the Environment

Chemical Encounters: The Elements and the Environment

Periodic

Properties of

the Elements

Our planet is composed of a wide variety

of elements.

Go to college.hmco.com/pic/kelterMEE for online learning resources.

7.1 The Big Picture—Building the

Periodic Table

The structure of the modern periodic table was initially conceived in the mid-

nineteenth century by scientists trying to make sense of the properties and

reactivities of all the elements found in the natural environment. It developed

through the recording of experimental results. That its structure is consistent with

the quantum mechanical understanding of the electronic structure of the ele-

ments that scientists arrived at in the early twentieth century, as we discussed in

Chapter 6, indicates the crucial role of electron arrangement in determining an

atom’s reactivity. It also conﬁrms the power of the periodic table as a classiﬁcation

260

We live on and within a big globe of chemi-

cals that have interacted for well over 4 billion

years to form the materially closed system that we call

the planet Earth. Our atmosphere provides the oxygen

molecules that interact with hemoglobin in our blood

and support life on this planet. The foods we eat help sus-

tain this life, and they include molecules with common names

like carbohydrates, proteins, and vitamins, as well as salts such as

sodium chloride. Our quality of life is enhanced by our clothing, which

is often made by combining molecules processed from crude petroleum

found deep beneath the seabed. The materials that we have produced for

cooking, cleaning, killing, and healing through the ages, from the Stone Age to

the Bronze Age to the Iron Age all the way through to the industrial revolution

of the late eighteenth and nineteenth centuries and on to the Information Age

that has deﬁned the twenty-ﬁrst century, have a common origin.

Throughout the ages, the stuff of life and of our way of life have been based on

the set of chemical elements listed in the periodic table.

Why is the oxygen (O

) that we must breathe every minute a gas, whereas

the gold we can dig up from the Earth to use as jewelry is a dense solid? Why

does this gold last for thousands of years, unchanged, while the oxygen reacts

so readily with many other elements and compounds? Why is the oxygen that

is carried around by our blood bound to the iron ions that form part of the

protein hemoglobin in our red blood cells? What makes iron so well suited to

this task? We need answers to these types of questions if we are to understand

the natural environment in which we live, its effects on us, our effects on it,

and how it is that we interact with it to acquire and process materials that are

so much a part of our day-to-day lives.

Our focus in this chapter is on the elements themselves and on how we use

the understanding of their basic structure that we developed in the last chap-

ter to gain insight into their chemical behavior. In the next two chapters, we

will look at how and why the elements interact with each other to form the

compounds that support our twenty-ﬁrst-century life. As we continue our four-

chapter atomic and molecular tour, we keep in mind that the greatest single statement

of our understanding of the behavior of the elements is the periodic table into which

they have been organized. It is there that we begin our discussion.

Oxygen.

Gold.

Video Lesson: Periodic

Relationships

system that becomes more meaningful and valid with each

new chemical discovery.

The structure of the periodic table includes “blocks” de-

ﬁned in terms of which type of orbital is being ﬁlled via the

Aufbau principle. This gives us the s-block, p-block, d-block,

and f-block, illustrated in Figure 7.1. Elements in the

s-block, such as sodium, potassium, and calcium, are natu-

rally found as positive ions, such as the Na

ion found in

seawater and the Ca

ion that characterizes “hard” well

water. Elements in the p-block often form negative ions; ex-

amples include the Cl

−

ions in blood and the S

2−

ion that is

a part of the minerals shown in Figure 7.2, such as pyrite

(FeS

), called “fool’s gold” for its goldlike appearance, and

galena (PbS), mined as the main source of lead metal. Many

elements in the d-block can form positive ions with different

charges. For example, iron can form the fairly stable Fe

and Fe

ions and also, as part of more complex molecules

and ions, the somewhat less stable Fe

,Fe

, and Fe

ions.

7.1 The Big Picture—Building the Periodic Table 261

La*

†

104

105

106

107

108

109

110

Uun

111

Uuu

IIIB

IVB

VIB

VIIB

IIB

100

101

102

103

Transition elements

d-block

IIA

IIIA

IVA

VIA

VIIA

VIIIA

Metals

Metalloids

Nonmetals

*Lanthanides

†

Actinides

112

Uub

Period

VIIIB

810

Main-group elements

s-block

Main-group elements

p-block

Inner transition

elements

f-block

FIGURE 7.1

The main ways in which we divide the periodic table into different sections. The s-, p-, d-, and f-blocks contain elements with outer electrons in the

same type of orbital. The horizontal rows are referred to as periods. The vertical columns are called groups. The color coding indicates the metals,

metalloids, and nonmetals. Helium is misplaced in the typical periodic table; it should be located next to hydrogen in the s-block.

The careful recording of experimental results made it possible to

determine physical properties of the elements that occur in the

natural environment.

262 Chapter 7 Periodic Properties of the Elements

Helium atoms are small enough to

escape from a balloon.

We see, then, that there is some relationship between the blocks in which ele-

ments reside and their chemical and physical properties.

The horizontal “period” of the periodic table to which an element belongs in-

dicates how many energy levels contain electrons in the ground state of atoms of the

element. Elements in Period 1 have electrons in only the ﬁrst energy level (princi-

pal quantum number n =1). Elements in Period 2 have electrons in the ﬁrst two

energy levels (principal quantum numbers n =1 and n =2), and so on. The more

occupied energy levels an atom has, the bigger will be the atom. Helium atoms,

from Period 1, are tiny compared to radon atoms, from Period 6. The tiny size of

helium atoms explains why a party balloon ﬁlled with helium deﬂates in just a

few days, as the atoms escape through little pores in the material of the balloon.

Again we see that position in the periodical table is related to what elements do.

Another key link between electron arrangement and position in the periodic

table is that elements in any one main group (Groups IA through VIIIA) have the

same number of electrons in their highest energy level, so that the members of

Group VIIA all contain seven electrons in their highest energy, or valence, level.

FIGURE 7.2

Iron pyrite, FeS

(left), and galena PbS (right). The sulfur

in these two minerals has gained electrons and exists

as S

2−

in PbS and S

−

in FeS

Day 1 Day 8

Groups

Periods

Periods and groups in the periodic table.

That is essentially why elements from each main group share some very signiﬁ-

cant chemical characteristics—why helium and neon are both unreactive gases,

for example.

HERE’S WHAT WE KNOW SO FAR

■

The periodic table is organized into blocks. The s-block, p-block, d-block, and

f-block indicate the orbitals that are partially full in the highest energy level of

the element.

■

Rows in the periodic table are known as periods. The period number indicates

the highest energy level in which electrons are found in the ground state on

each element.

■

Columns in the periodic table are known as groups. Elements in the same

group have the same number of electrons in their highest energy level.

■

Elements in the same group have similar properties.

EXERCISE 7.1 Identifying Elements

Give the block, the period number, and the group number for each of these

elements.

K, Sc, Al, C, Br

Solution

Potassium is an s-block metal found in Period 4 and Group IA.

Scandium is a d-block metal found in Period 4 and Group IIIB.

Aluminum is a p-block metal found in Period 3 and Group IIIA.

Carbon is a p-block nonmetal found in Period 2 and Group IVA.

Bromine is a p-block nonmetal found in Period 4 and Group VIIA.

PRACTICE 7.1

Identify each of these elements.

a. A p-block element in Period 5 and Group IVA.

b. A d-block metal from Period 6 and Group VB.

c. An s-block element in Period 1 and Group IA.

See Problems 3–6.

The Historical Development of the Periodic Table

We have just summarized the structure of the periodic table from a modern “elec-

tron arrangement” viewpoint. However, the ﬁrst recorded steps in building the

table were made from the quite different viewpoint of the experimental chemist

observing what the elements actually do when they react with one another. These

ﬁrst steps were taken by the German scientist Johan Dobereiner (1780–1849)

when he identiﬁed several groups (he called them triads) of elements whose

properties were very similar. Dobereiner’s “triads” included lithium, sodium,

and potassium (now found in Group IA of the modern periodic table), calcium,

strontium, and barium (now in Group IIA), and chlorine, bromine, and iodine

(Group VIIA).

In 1864, Englishman John Newlands (1837–1898) arranged some elements

in order of increasing atomic mass and found that similarities in properties

7.1 The Big Picture—Building the Periodic Table 263

40.078

87.62

137.327

35.453

79.904

126.904

32.066

78.96

127.60

The three triads of elements

discovered by Dobereiner.

occurred in elements eight places apart in his scheme. Newlands’s system of ele-

ments, arranged in what he called octaves (an octave is a musical interval of eight

tones, as in the eight white keys on the piano from one C note to another) pro-

vided an early glimpse of the regular repetition, or periodicity, in properties that

gives the periodic table its name. We know today that the elements have to be

arranged in order of increasing atomic number for the periodic nature of the

periodic table to be observed.

The modern form of the table ﬁrst began to take shape through the work of

German chemist Julius Lothar Meyer (1830–1895) and Russian chemist Dmitri

Mendeleev (1834–1907). They added many more elements to the table, and

Mendeleev took the crucial step of predicting that certain elements must exist to

occupy the gaps that were left in the table. In 1869, Mendeleev published the pe-

riodic table shown in Figure 7.3. Within a few years of Mendeleev’s predictions,

three elements were discovered that matched these predictions and ﬁlled some of

the gaps. For example, Mendeleev predicted the existence of the element “ekasili-

con,” which we now know as germanium; it was discovered in an ore called argy-

rodite by the German chemist Clement Winkler in 1886. Table 7.1 gives some of

germanium’s properties as predicted by Mendeleev and as later measured after

the element was discovered. The other two elements discovered were ekaboron

(scandium) and ekaaluminum (gallium).

Mendeleev’s realization that the periodic table could be used as a predictive

tool is probably the main reason why Mendeleev, rather than Meyer, is now

264 Chapter 7 Periodic Properties of the Elements

John Newlands noticed that every

eighth element had similar properties,

a principle that he called the law of

octaves. Eight consecutive white keys

on a piano comprise an octave.

Dmitri Mendeleev (1834–1907), the

youngest of the 17 children in his family,

was born in Serbia. After his father died,

his mother moved the family to St. Peters-

burg, Russia, so that Mendeleev could get

the best education possible. After 20 years

of work, he developed the basic layout of

the periodic table that we still use today.

Predicted (Ekasilicon) and Measured Properties of Germanium

Ekasilicon (Ek) Germanium (Ge)

Predicted in 1871 Discovered in 1886

Atomic mass = 72 Atomic Mass = 72.6

Density = 5.5 g/cm

Density = 5.47 g/cm

Density of EkO

= 4.7 g/cm

Density of GeO

= 4.70 g/cm

EkCl

will be liquid, density = 1.9 g/cm

GeCl

is a liquid, density = 1.89 g/cm

TABLE 7.1

FIGURE 7.3

Mendeleev’s periodic table. The atomic mass of each of the elements is recorded in the table. Dashes in

the table indicate elements that Mendeleev proposed but had not yet been discovered. The symbols at

the top of the table (R

O, RO, R

, etc.) are chemical formulas written in the style of the 1870s.

Video Lesson: Creating the

Periodic Table

7.2 The First Level of Structure—Metals, Nonmetals, and Metalloids 265

recognized as the “father of the periodic table.” What we now appreciate as posi-

tively inspired reasoning was, at one time, dismissed as Mendeleev’s madness—a

telling illustration of how the scientiﬁc method requires time for important in-

sights to be identiﬁed among other, less fruitful ideas.

7.2 The First Level of Structure—

Metals, Nonmetals, and Metalloids

The periodic table hangs in a highly visible place on the wall of chemistry labora-

tories all over the world. It is not there for reasons of history or adornment. It

is there because it is the most important and useful work developed in the history of

science for describing what we know about the chemistry of the elements. There are

many versions of the table, and they vary in precisely what information is given

about each element. The basic structure of the table, however, in terms of the po-

sitioning of elements within vertical groups and horizontal periods, is generally

the same. A chemistry student from Russia, South Africa, Mexico, or Scotland can

look at the table and communicate its ideas with any other chemistry student in

the world. The language of chemistry, as illustrated by the periodic table, is uni-

versal. What does this basic structure tell us about the elements?

The elements in the periodic table are arranged into three main sections—the

metals, nonmetals, and metalloids (or semimetals)—as shown in Figure 7.1. The

majority of elements are metals, which possess a variety of “metallic” character-

istics, including those in this list.

Metals are generally

■

shiny in appearance

■

solids at room temperature and pressure (apart from mercury, the only metal

that is a liquid at room temperature and pressure)

■

good conductors of electricity

■

malleable—that is, able to be hammered into various shapes

■

likely to form positively charged ions when they react to form ionic

compounds

Metals, including iron, aluminum, and copper, supply us with some of our most

widely used and versatile materials for fabrication. For example, copper is used

in electric wires and in plumbing throughout your home. Iron is the basic

Copper is not very reactive—hence its

use in electrical wire and pipes.

Selected Metals, Their Sources, and Their Uses

Metal Major Sources in Nature Uses

Al Bauxite, clay, mica, feldspar, alumina Food wrap, kitchenware, beverage cans

Ca Lime (CaO), limestone (CaCO

), feldspar, apatite Manufacture of vacuum tubes, alloys, preparation of

other metals

Cu Chalcopyrite (copper iron sulﬁde), pure metal Coinage metal, electric wires, plumbing pipes

Fe Hematite (Fe

), limonite (Fe

·3H

O) Steel

Na Salt (NaCl), Borax (Na

·10H

O) Street lamps, nuclear reactor coolant

Ni Pentlandite and pyrrhotite (nickel–iron Coinage metal, stainless steel, NiCad batteries,

sulﬁdes), garnierite (nickel–magnesium silicate) heating elements

Sn Casserite (SnO

) Tin cans, many alloys, including bronze

Ti Rutile (TiO

), ilmenite Aircraft parts, lightweight tank armor

W Wolfram ochre (WO

) Filaments in light bulbs

TABLE 7.2

266 Chapter 7 Periodic Properties of the Elements

constituent of a homogenous mixture of metals (known as an alloy) that make up

steel. Steel is used throughout our modern world as a structural component of

cars, trains, buildings, and bridges.

What are the industrial and commercial uses of steel? Chromium and nickel are

used to create the familiar stainless steels. These steels resist corrosion and are

commonly used in making tableware. Tellurium and selenium promote the

machinability of steel, its ability to be easily turned and shaped into bolts and

screws. Manganese makes steels that are very resistant to wear as well as to chem-

ical reaction with water. Molybdenum is used to create hard steels for use in bear-

ings. Careful addition of silicon creates electrical steels used in the generation and

transmission of electricity. The exploration of ways in which subtle changes in

the composition of steels brings about signiﬁcant changes in their properties is a

continuing process. That huge research and manufacturing effort all stems from

the simple observation, hundreds of years ago, that letting hot charcoal mix in

with molten iron improved its usefulness.

EXERCISE 7.2 Heavy Metals, Both Necessary and Toxic

If you follow environmental issues, you may have heard of the term heavy metals,

which some think of as those with atomic masses greater than or equal to 63.546 g/mol.

Some of these metals are essential for life, but many of them are toxic. Some of the

heavy metals that are vital for life in low concentrations can be quite toxic in high

concentrations. Heavy metals in water and soil are a major focus of environmental

concern.

1. According to the deﬁnition given above, what is the lightest of the heavy

metals?

2. Using the periodic table, can you identify some other heavy metals that are

commonly discussed as environmental contaminants?

3. Chromium is included in some lists of heavy metals. What does that indicate

about the deﬁnition of the term heavy metals?

4. Can you suggest why heavy metals can be particularly persistent environ-

mental contaminants, posing problems that are difﬁcult to correct?

Solution

1. According to the deﬁnition supplied, copper is the lightest of the heavy

metals.

2. The metallic elements heavier than copper in the periodic table include many

that have received publicity as heavy metal contaminants of the environment.

Examples which feature prominently in news reports on this issue are cad-

mium, mercury, and lead.

3. Chromium has a lower atomic mass than copper, so its inclusion in lists of

heavy metals suggests that there is no universally accepted deﬁnition of the

term heavy metal. This is in fact the case. It is a term used rather loosely to

describe metallic elements of relatively high atomic mass that are also toxic.

4. Heavy metals are particularly persistent environmental contaminants because,

being elements, they cannot be degraded into simpler, less toxic components.

This is in contrast to toxic compounds, some of which are readily degraded

into less harmful compounds or their component elements.

PRACTICE 7.2

Which of these elements are metals? Which of these are heavy metals?

Li, Si, Ni, Ce, Ge, Al, Po, Se, Rb, Cu

See Problems 11 and 12.

Stainless steel is commonly used as ﬂat-

ware in kitchens.

7.2 The First Level of Structure—Metals, Nonmetals, and Metalloids 267

Steel, shown in Figure 7.4, is one of our

most versatile construction materials,

with 1.05 billion metric tons (2.42 trillion pounds)

manufactured in 2004. What exactly is steel?

The most basic deﬁnition tells us that steel is a mix-

ture of iron and small amounts of carbon, suggesting

that it is a metal with a little nonmetal blended into it.

Hundreds of years ago, it was discovered that the metal

element iron could be changed into a tougher and more

resilient material by allowing carbon from wood ﬁres

to become mixed in with it. Since then, we have discov-

ered that adding various other elements in differing pro-

portions can be used to vary the properties of steel in a

great many ways. In fact, nowadays, we can no longer

talk of steel as though it were a single thing. There are

actually over 3500 different grades of steel, each with a

particular mixture of elements added to the iron that

forms the basis of them all. Looking at the differences

among these grades reveals how small changes in the

atoms present in the steel can have very signiﬁcant ef-

fects on its properties.

There are three main types of steel, known as carbon-

steel, low-alloy steel, and high-alloy steel. Carbon-steels

have as little as 0.1% and sometimes more than 2%

carbon added to their iron, but only very small amounts

of other elements. Over 90% of the world’s steel is carbon-

steel, which is further categorized as high-carbon,

medium-carbon, low-carbon, ultra-low carbon, and so

on, depending on exactly how much carbon it contains.

Alloy steels have homogeneous mixtures of metals, called

alloys, added to them. The metals most commonly added

to alloy steels are manganese, aluminum, copper, nickel,

NanoWorld / MacroWorld

Big effects of the very small: The diversity of steels

FIGURE 7.4

Steel, such as that being poured here,

has a variety of uses in the manufac-

ture of building materials, ofﬁce equip-

ment, and automobile parts.

chromium, cobalt, molybdenum, vanadium, tung-

sten, titanium, niobium, zirconium, and tellurium.

Steels also often contain some added nonmetals, such

as silicon, selenium, nitrogen, and sulfur. The compo-

sitions of three standard steels are shown in Table 7.3.

The enhanced strength of the iron–carbon alloy was used initially to create

swords and armor.

The Compositions of Selected Steels

The elements alloyed with iron to make selected

steels. The numbers are reported as the mass percent

of the total composition.

Tool Basic Electric Stainless

Steel Steel Steel

C 0.864 0.215 0.225

Mn 0.341 0.393 0.544

P 0.012 0.016 0.030

Si 0.185 0.211 1.00

Cu 0.088 0.211 0.226

Ni 0.230 0.248 8.76

Cr 4.38 0.017 16.7

V 1.83 0.003 0.176

Mo 4.90 0.038 0.24

W 6.28 — —

Sn 0.029 — —

Al — 0.002 —

Co — — 0.127

TABLE 7.3