Phosphorus and its compounds [1, 1 ed.] 0470900571, 9780470900574

Table of contents :
Front Cover
Title Page (Page iii)
Copyright (Page iv)
Table of Contents (Page xi)
Section 1 (Page 1)
Section 2 (Page 21)
Section 3 (Page 61)
Section 4 (Page 93)
Section 5 (Page 179)
Section 6 (Page 265)
Section 7 (Page 345)
Section 8 (Page 419)
Section 9 (Page 479)
Section 10 (Page 601)
Section 11 (Page 679)
Section 12 (Page 717)
Section 13 (Page 801)
Section 14 (Page 845)
Section 15 (Page 887)
Index (Page 892)
Section 16 (Page 921)
Index (Page 922)

Citation preview

UNIVERSITY OF CALIFORNIA MEDICAL CENTER LIBRARY SAN FRANCISCO

PHOSPHORUS AND ITS COMPOUNDS In two volumes

Volume Volume

I: CHEMISTRY

II: TECHNOLOGY, FUNCTIONS. AND APPLICATIONS

The compound C1CHSP(0)CI2 showing n-bonding between the gray phosphorus atom and the two green chlorine atoms and single red oxygen atom attached to it. The van dcr Waals' radii of the atoms are denoted by the cloud surrounding the molecular structure.

PHOSPHORUS and

its COMPOUNDS In Two Volumes

I: CHEMISTRY

Volume

JOHN R. jVAN WAZER Assistant Research Director and Senior Scientist, Inorganic Chemicals Division, Monsanto Chemical Company, St. Louis, Missouri

1

9

m

5 8

INTERSCIENCE PUBLISHERS, INC., NEW YORK INTERSCIENCK

PUBLISHERS LTD., LONDON

Copyright © 1958 by Interscicnce Publishers, Inc. Library of Congress Catalog Card Number 58-10100

INTKUSCIENCE PUBLISHERS, INC.,

250

Fifth Avenue, New York

1,

N. V.

Kor Great Britain and Northern Ireland:

Interscience Publishers Ltd., 88/'.K) Chancery Lane, London, VV.C.

PRINTED

IN THE I'NITBl) STATK* OK AMERICA

BY MACK PRINTING

2

CO.,

EASTON. PA.

QD

Tl

V2. v.l

Dedicated to

BETTY

1J

and

8822

BETH

mene mene (ekel upharsin Daniel, 5, 25

PREFACE The purpose of this book is to lay

discipline

of chemistry

for a new, separate Up to now, descriptive

a foundation

— phosphorus chemistry.

chemistry has been divided into two parts: organic chemistry, which treats of carbon compounds; and inorganic chemistry, which covers all that is left over. As now presented to the undergraduate student, organic

chemistry is a beautifully systematic and self-consistent discipline, whereas inorganic chemistry has been somewhat of a hodge-podge of unrelated facts and often misguided fancy. Because of this, inorganic chemistry offers a tremendous challenge — a challenge which is being accepted by a sufficient of persons today so that inorganic chemistry is undergoing a powerful renaissance. Three factors have made this renaissance possible. One of these — and perhaps the most important one — is the new qualitative and quantitative understanding of the interaction between atoms brought number

about by quantum mechanics in its two applicable forms — valenceAnother is the armament of power bond and molecular- orbital theory. ful, new, structure-sensitive tools which have become generally available

during the last decade or two for studying inorganic systems.

The

use

of chromatographic methods, nuclear magnetic resonance, the techniques of polymer physics, as well as the older methods of x-ray and electron diffraction and vibrational analysis (infrared and Raman) point up the

deficiencies of relying completely on wet-chemical analytical procedures for information, as has been done during most of the century and a half that inorganic chemistry has been a major chemical discipline. The third factor which has led to the inorganic renaissance is the ever-

manyfold

commercial interest in production of inorganic chemicals — due in part to the fact that automation (the spirit of our Age) is so adaptable to inorganic processes which are run at large volumes. widening

But enough of inorganic chemistry, for this book treats of a different Just as the organic chemist may develop subject — phosphorus chemistry.

the theme of, say, organic compounds vii

of sulfur or of phosphorus

—so I

viii

I'KEFACE

have discussed the phosphorus compounds containing carbon from the view point of a phosphorus chemist. In this book, no differentiation is made between the "inorganic" and the "organic chemistry" of phosphorus,

except for the fact that the available data were obtained by persons having quite divergent philosophical viewpoints so that synthesis techniques, regardless of yield, are necessarily emphasized for the phosphorus com pounds of carbon as opposed to phase relationships, crystal chemistry,

and the like for the phosphorus compounds of other elements. In setting up a philosophy for the nascent discipline of phosphorus chem istry, I have tried to take the best from both inorganic and organic chem istry. However, the spirit of the inorganic renaissance pervades this book,

probably because a new discipline cannot afford the lordly but sketehy approach essayed by the organic chemist from the ramparts of his detailed

chemical system. Is it not sufficient And now you ask, why speak of a new discipline? of to formalize the chemistry phosphorus compounds within the confines of organic and the now rapidly developing inorganic chemistry? What a needless conceit to attempt the establishment of a new discipline.

And I answer that there is a real need for a separate discipline just as there was a need for separating the chemistry of carbon compounds from the rest of chemistry. Instead of being merely a ragtag collection, the compounds of carbon are readily arranged into homologous series, and a small number of ground rules have proved sufficient to describe the re lationships and interactions between these homologous series and between members of a given series. This state of affairs also seems to apply to the

The phosphates, the phosphonitrilic chlorides, compounds of phosphorus. and other groups of phosphorus compounds are truly homologous series. Furthermore, a system of ground rules, in some cases quite different from those of organic chemistry, appears to be emerging. Is this not a good

reason for approaching the compounds of phosphorus with a fresh viewpoint and as a special topic? In addition to its homologous series and rules, organic chemistry is also unique in that molecular structures can be built from "plans," by a process

I call "positional synthesis." Very little is said in this book about positional synthesis in phosphorus chemistry because very little has been done along these lines. However, there seems to be ample reason to which

believe that methods of positional synthesis can be developed specifically This is an important challenge for the future. for phosphorus chemistry. Although the renaissance in inorganic chemistry is so new that it is difficult to predict its outcome, a broad pattern does seem to be emerging.

l'KKFACK According to this pattern, separate chemistries will probably be developed for those elements lying near carbon in the Periodic Table. This book represents an attempt in this direction for one such element— phosphorus. Throughout this book an effort has consistently been made to present available data in a form which will be useful to workers in the various areas This means that, in some cases, extrapolations of phosphorus chemistry.

were employed and certain data were reworked and extended on the basis of the theories presented herein. In these cases, the text clearly states that There are also occasional the experimental findings were enlarged upon.

places where the data obtained by a certain author are used to prove a In point which is in complete opposition to the original author's ideas. cases where these original ideas are still believed by some people, a com ment is usually made in the text that the interpretation given herein differs from the original. universally

However, where the earlier interpretations are quite accepted as being obsolete, no mention is made of the rein-

terpretation. No attempt

the literature on phosphorus and its compounds. Indeed, it would take a book several times the size of this one to survey completely the literature on either the organic or the inorganic compounds of phosphorus. However, it is hoped that all of the classes of compounds (either organic or inorganic) which has

been

made to review exhaustively

have received a reasonable amount of study are covered herein and that sufficient literature references are presented to enable the scholar to locate

easily the entire literature on any particular subject of interest. I wish to thank Julia D. Behrens for carrying out the extensive clerical work involved in preparing the manuscript of this book. Thanks is also

In proofreading. addition, I wish to acknowledge the technical assistance of John R. Parks in writing Chapter 12 and of Edmund Churchill of Antioch College in carrying out the mathematical calculations given therein. A review of due to Celeste

Frank for preparing

the index and

phosphides prepared by Richard G. Yalman of Antioch College has also been of value in writing Chapter 4. In addition, I also gratefully ac

knowledge the corrections made on the page proof by John H. Payne, Donald P. Ames, Clayton F. Callis, John W. Cross, Allan D. Gott, Edward J. Griffith, Thomas L. Hurst, Chung Yu Shen, and Fritts W. Thomas, of

Monsanto. Walter H. Maclntire, formerly of the University of Tennessee, John W. Gryder of Johns Hopkins University, and Oscar T. Quimby of Procter and Gamble have also assisted materially in improving the quality of this book. The continued encouragement and moral support of John L. Christian, Vice-President of Monsanto, have been greatly appreciated. Without his backing, this book could not have been written. John R. Van Wazer St. Louis, Missouri May, 1958

CONTENTS

1.

The Phosphorus Atom, Its Nucleus and Electronic Structure Atomic Weight Nuclear Structure Atomic Structure Summary

1 1

2 6 19

2. Interaction between Atoms, with Especial Reference to Phosphorus Chemistry

The Periodic Table Bond Energies Bond Lengths Structures from Nuclear Magnetic Resonance Dipole Moments and Polarity of Molecules Ionic Radii Nonbonded Radii Summary

of Phosphorus and Its Compounds Introduction Essentials for a Systematic Covalent Chemistry Kinds of Phosphorus Compounds Chemical Reactions Bond Notation and Classical Chemical Theory Nomenclature

3. Systematic Chemistry

4. Elemental Phosphorus and the Metal Phosphides

History Elemental Phosphorus White Phosphorus Red Phosphorus Black Phosphorus The Phosphides

21 21

28 34 43 53 57 59 59 61

61 62 70 77 83 87 93 93 93 106 114 119 123

Halides, and Pseudohalides Derivatives History The PH Molecule Phosphine Phosphonium Compounds Lower Hydrides of Phosphorus Phosphorus Halides Spectroscopic Molecules PX Phosphorus Trihalides Phosphorus Dihalides Phosphorus Pentahalides Phosphorus Polyhalides

5. Hydrides,

xi

of Phosphorus and Their Organic

179 179 179 180 207 215 219 220 220 234 236 242

xii

CONTENTS Phosphorus Oxyhalides Thiophosphoryl Halides Phosphorus Halogenoids Organic Derivatives of Phosphorus Halides

245 268 259 261

6. Oxides, Sulfides, Nitrides, and Related Compounds of Phosphorus

265

History Spectroscopic Molecules Phosphorus Oxides Phosphorus Sulfides Phosphine Selenides and Tellurides Un-ionized Phosphorus-Nitrogen Compounds

7. Lower Oxyacids of Phosphorus,

History

Their Salts

265 266 267 289 308 309

and Esters

345

General Discussion. Acids, Salts, and Esters Based on One Phosphorus Atom Acids, Salts, and Esters Based on More Than One Phosphorus Atom

of the Condensed Phosphates History Basic Principles of Phosphate Structures Differential Analysis of Phosphate Mixtures Comparison of Condensed Phosphates with Condensed Oxyacids of Other Elements Formation of Condensed Phosphates Hydrolytic Scission of P — O — P Linkages in Chains and Rings Association of Phosphates with Cations in Solution Effects of Phosphates on Colloids Electrical, Mechanical, and Optical Properties of Phosphate Solutions

8. Structure and Properties

9. Orthophosphoric Acid, Its Salts and Esters

History Orthophosphoric Acid Alkali Metal Phosphates Calcium Orthophosphates. Other Inorganic Phosphates Heteropoly Acids of Phosphorus Organic Orthophosphates

10.

346 353 390 419 419 421 441

446 450 452 459 468 471

479 479 479 491

,

Chain Phosphates (Pyro-, Tripoly-, Tetrapoly-, as Well as Kurrol's and Maddrell's Salts) General History Crystalline versus Amorphous Compositions Polyphosphate Phase Diagrams. Pyrophosphates

Individual

phosphates

Tripoly phosphates

345

Tetrapolyphosphates Individual Polyphosphates Larger Than the Tetra Kurrol's and Maddrell's Salts

510 538 559 570 and

Pentapoly-

601 601

602 604 617 638 660 662 665

contexts 11. Ring and Branched Phosphates

History General Behavior of Ring and Branched Phosphates Ring Phosphates ' Branched Phosphates

12. Amorphous Phosphates, Including Phosphate Glasses, Condensed Phosphoric Acids, and Phosphate Esters Introduction and History Reorganization Theory Experimental Size Distributions Compared with Theory Physical and Chemical Properties

Peroxy-, Thio-, and Amidoacids of Phosphorus, Their Salts, Esters, and Related Compounds Introduction The Haloacids and Their Derivatives Peroxy acids of Phosphorus Thio Salts and Esters Ami do- and Imidoacids, Their Salts and Esters Tin and Arsenic Analogs of Phosphonic Acids

xiii 079 679 680 681 706 717 717 722 744 770

13. Halo-,

801 801 802 821

824 830 843

Appendix A.

Phosphate Minerals

845

Appendix B.

A Collection of Single Bond Energies and Distances, etc.

887

Appendix C.

Available Thermodynamic Data on the Compounds of Phosphorus

888

Author Index

891

Subject Index

921

CHAPTER

1

The Phosphorus Atom, Its Nucleus and Electronic Structure

ATOMIC WEIGHT with an atomic number of 15, has six reported isotopes. with odd atomic numbers exhibit no more than two stable iso Elements In accord with the laws of topes; for phosphorus, there is one,1 lsP'1. nuclear stability (modified Harkins' rules'), this stable isotope has an odd mass number, 31, to correspond with its odd nuclear charge, 15. The mass Phosphorus,

number of

the closest whole number to the physical atomic weight of 30.9840 computed from nuclear reaction data and supplemented by mass spectrograph measurements.* This physical atomic weight is referred to 31 is

the mass of the

8014

On the other hand, chem isotope taken as 16.000000. used in chemical calculations — are based

ical atomic weights —universally

on the average mass of the naturally occurring mixture of jO", sO17, and Although the naturally occurring mixture »018 being equated to 16.00000. of oxygen isotopes has been shown to vary somewhat from source to source,

the chemical atomic weight can be calculated from the physical one by 1.00028 — a factor based on an average relative abun

dividing the latter by

dance of the three oxygen isotopes. The presently accepted [1952] chemical atomic weight4 of 30.975 for the single naturally occurring isotope of phos phorus was calculated by dividing the physical atomic weight by this fac

tor. Chemical methods have not been used to evaluate the atomic weight of phosphorus since 1939, when a value of 30.98 was accepted,4 primarily

L. Kerwin, Can. J. Phys., 32, 757 (1954). T. MoeUer, Inorganic Chemistry, John Wiley Sous, New York, 1952, pp. 25-9. H. T. Motz, Phys. Rev., 85, 501 (1952) [nuclear reaction data: 30.9840); H. Ewald, Z. Naturforsch., 6a, 293 (1951) [mass spectrograph: 30.93622 ± 0.00023]; C. D. HodgP'!, which is made on a commercial scale in Oak Ridge by the S-n-p or P-n-7 reactions. The mate rial from the S-n-p process can be obtained in an isotopically pure form. The manufacture12 of the purified i5P82 is carried out by irradiating about

purified sulfur in a large aluminum can in the atomic pile for about 6 weeks. This irradiation results in about 800 millicuries of i6P,J and 350 millicuries of i«S36 (half-life of 87 days) and some short-lived

2 kg. of specially

activities which decay to insignificance before the sample is shipped. The irradiated sulfur is melted out of the can, and the radioactive phosphorus, along with a small amount of the sulfur, is extracted with 0.2

A. Alpher and R. C. Herman, tary presentation, see G. Gamow, The 1952, pp. 44-73. 11 J. M. Hollander, I. Perlman, and N. Butler and W. Y. Gissel, Washington, D. C, Dec. 10, 1947.

N nitric

acid

10 R.

Revs. Mod. Phys., 22, 153 (1950);

"J.

G. T. Seaborg, Revs, ^fod. Phys., 25, 469 (1953). AECD-2850, V. S. Atomic Energy Commission,

for an elemen

Creation of the Universe, Viking Press, New

York,

1.

Phosphorus Atom, Nucleus and Atomic Structure

5

TABLE 1-2" Radioactive Isotopes of Phosphorus

Isotope

Methods of production Si-p-n

Decay Type product, of (stable decay isotope) n+

.«si»

Halflife 4 . 6 sec.

Energy of 0-rays

cal

(M.e.v.)

(M.e.v.)

3.6

1.28

28.983

(2.5%) 2.42 (0.5%)

P-7-2n Si-p-n Si-»He-p P-n-2n P-y-n

Chemi atomic weight

Si-d-n

Al-or-n

Energy of 7-rays

/?

+

iSi*

2.5 min.

29.980

3.4

S-d-a

uP"

CUyan

Si-d-7

14

Si-or-p

.3 days

Si-»He-p P-d-p

1.701

(100%)

None

31.975

P-n-7 S-n-p S-d-a CI-n-a

Cl-7-an Cl-d-pa Fe-high energy fission

Cu-high energy fission

S-n-p S-7-p

0~

,$»

25 days

S-n-p Cl-n-a

None

5.1 (75%) 3.2 (25%)

Present

(100%)

Cl-7-a

Cl-7-2p

0.26

„S"

at 120-140°C. under pressure.

12.5 sec.

—

The molten sulfur phase is removed from the reactor, and the acid phase is filtered and treated with sodium hydroxide to remove corrosion products. After acidification with hydrogen chlo ride, the phosphate is precipitated with ferric or lanthanum chlorides to separate it from that radioactive sulfur which had been oxidized by the

Phosphorus and ft* Compounds:

li

Volume

I

nitric acid.

The phosphate precipitate is then dissolved in hydrochloric acid and run through an ion-exchange column to remove the lanthanum or iron and other cations. After evaporation to dryness to volatilize the hydrogen chloride, the resulting phosphoric acid is redissolved in water and

neutralized with sodium hydroxide before filtration through a sintered glass disk to remove any silica or foreign matter that might be present. The final solution contains about 0.5 millicurie per milliliter. Its Phosphorus-32 has nearly ideal characteristics for tracer studies. beta radiation is sufficiently energetic so that any type of beta counting

unit, including glass-walled Geiger-Muller tubes, can be used. Correc tions for self-absorption are also seldom needed for thin samples having this energy radiation. Also, many studies can be carried out without making allowances for radioactive decay. Thus, in 1 hour 99.80% of the original

activity

still present and in

Stock solutions can be stored for appreciable lengths of time, since the activity diminishes to l/s in 2 weeks, 'A in 1 month, and 1/m in 2 months. is

24 hours 95.3% remains.

ATOMIC STRUCTURE Thus far, this discussion

having

has been

concerned with the various nuclei neutralize 15 electrons.

to exactly

charge sufficient According to the most recent concepts, the nucleus can be pictured as an It is surrounded by a exteriorly diffuse ball, about 10-12 cm. in radius. number of electrons, usually 18 (6 or 8 of which are shared) for the phosphorus a positive

atom in the normal ranges of temperature and pressure. These electrons Since the radius of are diffuse negative charges with essentially no mass. an atom can be shown from the packing in crystals to be equal to about 10-7 cm., there is well over a

trillion times more vacant than filled space

within the atom, with the mass essentially all concentrated in the nucleus.

Since the nuclear quadrupole moment is zero for phosphorus, the charge distribution in the phosphorus nucleus is spherically symmetrical. The nuclear radius reported above represents the radius in which most of the energy (or mass) of the nuclei is contained. However, quantum me chanical reasoning has shown that the elemental particles do not exhibit but simply fade away into nothingness.

a discrete boundary

Orbitals The usual discussion of the distribution

of electrons about an atomic nucleus is based on concepts and notation specifically designed for the inter pretation of spectrographic data. Thus, the basic states refer to isolated

1.

Phosphorus Atom, Nucleus and Atomic Structure

atoms and their ions, such as occur in gaseous discharges, rather than to the chemically bonded atoms. According to this notation, the first stable elec tronic configuration is called the ls-orbital, and two electrons with opposed

700

600

500

400 IONIZATION

POTENTIAL

(ELECTRONVOLTS)

300

200

100

p+3

STATE ELECTRONS

I 15

Fig. 1-1. The successive

1

n 14

13

12

II

10

9

8

2I2IL 7

6

ionization potentials of phosphorus. mole.)

5

(1 e.v.

4

= 23.06

kcal./

The element spins fill this orbital to form a complete K -shell of electrons. helium exhibits an electronic structure corresponding to a completed KThe next outer shell of electrons is called the L-shell and is filled by shell. a pair of electrons in the 2s-orbital and three pairs of electrons in the 2p

Phosphorus and Its Compounds:

8

orbital. neon.

Volume

I

A completed L-shell of eight electrons is found for the inert

The

M-shell

gas,

contains one electron pair in the 3«-orbital, three pairs Argon corresponds to and five pairs in the 3°5s85p«

5/

6d

7s

«

Is8

and

6

4d'05s'5p>

4d

5 6

Is8

4

Zd'HsHp'

Fr,

Au, Ra

Hg,

Cd Ba

Cs,

Sr

Zn

Ag,

Rb,

Cu,

Ca

Ge,

N,

electrons)

p-Orbital

As,

Tl,

Pb,

Bi,

In, Sn, Sb,

Ga,

2-1

Ne

Po,

Te,

Se,

CI,

At,

Rn

Xe

Br,

Kr

Highest

I,

Is8

Is8,..

Is8

p

« s

1««

Is1

p

s

Is'

1 2 3 4 p

and

p p

5«

K,

Si,

Al,

Mg

Li, Be Na,

H, He

B,

3d

elec

trons)

C,

ls*2st2p,3s*3p*

s s s s and

and

shell)

(valence

0, S, P,

Is8

Is1

None

shell)

below

«Orbital

TABLE

by the Electronic

(6

l^^2^s2p•3s,3p,l

valence

being filled

of the Elements

F, A

l8*2st2ptZst3p*3d">

the

(electrons

configuration

Inner

Shell

Classification

(2 Ac

Lu,

La

Y,

Os,

Ta,

VV,

Mo,

Cr,

Pd

Ni

Ir, Pt

Rh,

Nb,

Co,

Hf,

Ru,

Zr,

Fe,

Ti,

(10 electrons)

Re,

Tc,

Mn,

in the valence

in the Ground

d-Orbital

filled

Sc,

level

Configuration

V,

.

Bk,

Nd,

Cf

U,

Dy,

Pa,

Pr, Tb,

Th,

Ce,

/-Orbital

shell

State

Np,

Ho,

Pm,

Pu,

Er,

Eu,

Am,

Tm,

Sm,

(14 electrons)

Gd,

Cm,

Yb

) () (

stable

A (Mv),

known

227.0

Ac

89

long-form

100, meudelevium

of most

2-1.

226.05

Ra

88 58

are

isotope.

periodic not

232.12

Th

90

140.13

Ce

shown.

Atomic

table.

231.

Pa

91

140.92

59

Pr

60

92

144.27

Nd

weights

are

1952

series.

(243)

international

committee

series.

(245)

Bk

in

164.94

67

Ho

values.

Numbers

(246)

Cf

98

97 96

Cm

162.46

Dy

66 159.2

65

Tb 156.9

+Actinium

(243)

Am

(242)

Pu

Np

95

94

93

(237)

152.0

150.43

64

Gd

63

Eu

(145)

62

Sm

61

Pm

'Lanthanum

238.07

u

Fig.

(223)

Fr

87

Elements

173.04

fermium

(Fm),

mass

and

number

GASES

INERT

174.99

71

Lu

70

Yb

indicate 99,

169.4

69

Tm

parentheses

167.2

Er

68

VII

A

Phosphorus and Its Compounds:

2-)

I

Volume

The fact that interpretation of atomic spec phorus) became apparent.* tra in term? of electronic configuration correlates so nicely with the general scheme of chemical interrelationships exemplified by the periodic table is a major proof of the concept that the number and behavior of the extranuclear electrons, especially the outermost electrons, of an atom determines its chemical properties.

Periodic Variation of Electronegativities

and Ionization

The ability of atoms to attract and hold electrons in their valence shell decreases from top to bottom and from right to left in the period table.

I 0

, I

I Z

PERIODIC

343 I

,

,

\ZZ

I

ROW (PERIOD)

1

n

m

. EC

PERIODIC

.

T

1

VL

I

2E

GROUP

Fig. 2-2. Approximate values of electronegativities on Pauling's scale as a function of placement of the elements in the periodic table.

This ability, called electronegativity, at a minimum

electronegativity *

for francium, has been

is thus at a maximum for fluorine and

the heaviest alkali metal.

put onto

a quantitative

For further detailed information about the relationships

good text on general inorganic chemistry, such as ref. 4. »

L. Pauling,

J.

Am. Chem. Soc., 54, 3570 (1932);

2nd ed., Cornell University Press, Ithaca, N.

Y.,

1940,

The concept of basis by Pauling2 and

between

the elements see a

The Nature of the Chemical pp. 58-69.

Bond

2.

Interaction

Between Atoms

25

Pauling's method for defining electronegativities from thermody namic data is discussed in detail later in this chapter (p. 30). A graph of electronegativity values of the common elements as a function of their As might be expected, position in the periodic table is given in Figure 2-2. the division of the elements into metals, metalloids, and nonmetals can be

others.

done on the basis of electronegativity values. Thus, the metallic elements are seen to have electronegativities below about 1.5 on Pauling's scale,

whereas the metalloids lie in the electronegativity range of 1.5-2.0, and Even the nonmetals have electronegativities greater than about 2.0. though the electronegativity

vidual chemical bonds,

scale is

primarily designed for treating indi

a number of interesting correlations have been de

veloped between electronegativity and gross chemical properties, such as acid-base strength3 and hydride type.4

Ionization of Atoms as Function of Periodic Placement Although large oxidation numbers of 4, 5, and even 6 are ascribed to ele ments of high atomic number, such as uranium, there is no question but that these oxidation numbers do not correspond to the charge borne on the ionized atom but, instead, refer to covalently bound atoms which bear only a small charge— usually less than ± 2 electrons. Spectrographic data show that the ionization potentials are very high for all triply charged posi tive ions. The lowest ionization potentials for the formation of ions having a

+

3 charge from the neutral monatomic gas are found for the

Group

III

These potentials are 876 kcal./mole for B3+, 656 kcal./mole for Al,+, 572 kcal./mole for Sc3+, and 464 kcal./mole for Y3+. From this type of data and other reasoning, one can conclude that triply and quadruply charged ions can only be formed by elements of very large atomic number, metals.

if they are formed at all under normal chemical conditions. This concept that individual atoms can only exhibit small charges was first stated by Pauling6 as the "principle of electroneutrality."

Under normal chemical conditions (temperature below about 1000°C), most of the elements in the periodic table can form ions (i.e., the atom in question can bear an electrical charge that is not neutralized by opposite charges on neighboring atoms to which the first atom is covalently bonded). However, there is considerable evidence to show that boron, carbon, siliJ F. Gallais, Bull. hoc. chim. France, 14, No. 5, 425 (1947). T. Moeller, Inorganic Chemistry, John Wiley & Sons, Inc., New York,

4

06.

' L. Pauling, J. Chem. Soc., 1948, Matron Desser, I>i6ge, Belgium, 1948.

1461

(1948);

Victor Henri

1952, pp.

Memorial

405-

Volume,

Phosphorus

26

and Its Compounds

:

Volume

I

atoms seldom, if ever, bear an appreciable charge in their stable compounds. These elements have intermediate electronegativ ities (1.8-2.6) and, moreover, lie midway between the stable electronic configurations corresponding to the inert gases, so that complete ionization

con, and phosphorus

would lead to unconscionably high charges. Naturally, elements for which the electronegativities are neither high nor low have the best possibility for sharing electrons with other elements without either completely losing or capturing the electrons. The elements which lie close in the periodic table to the four elements listed above also tend to approximate closely the covalent-bond model in most of their compounds. The nonexistence of ionized phosphorus in solutions, solids, and prob ably in melts is substantiated by the ionization potentials shown in Figure 1-1.

Two hypothetical

ionic species

of phosphorus

cussed in the early or less precise scientific literature

which are often dis are the P'+ and P5+

ions. However, these ions have the extremely high gas-phase ionization potentials of 697 and 1500 kcal./mole, respectively, as compared to 119 kcal./mole for Na+ and 274 kcal./mole for CaJ+. Since the heats of chem ical reactions are usually less than a few hundred kcal./mole, there appears

to be no mechanism whereby the highly charged ions such as P3+ and P5+ can be stabilized in any environment. Proof that phosphorus is covalently bonded to its neighboring atoms is

given by complete x-ray analyses" in which detailed electron density projec tions have been calculated. From these electron density maps, it can be seen that the electrons are shared between each phosphorus atom and its

The existence of in oxygen atoms in the phosphates. direct spin-spin splitting7 in the nuclear magnetic resonance spectra of a number of phosphorus compounds also proves that phosphorus is covalently four neighboring

As explained in a bonded to its neighboring atoms in these structures. later section of this chapter, indirect spin-spin splitting occurs when the coupled nuclei, each exhibiting a spin, are so arranged that the same elec

trons circle all of them. In other words, the coupled nuclei are held to gether by covalent bonds. Indirect spin-spin splitting has been observed for a variety of compounds in which the phosphorus atoms are bonded to A third proof that phosphorus is cova 3, 4, 5, and 6 neighboring atoms. lently bonded to its neighboring atoms is found in the n—*-ir* spectrographs for example, C. Romers, J. A. A. Ketelaar, and C. H. MacGillavry, Acta Cryst., 4, 114 (1951); and S. Furberg, Acta Chem. Scand,, 9, 1557 (1955). 7 C. F. Callis, J. R. Van Wazer, J. N. Shoolery, and W. A. Anderson, J. Am. Chem. • See,

Soc., 79, 2719 (1957).

2.

transition.8

Interaction Between Atoms

The lowest energy transitions in many molecular

of this type, corresponding to the formation from a nonbonding orbital.

of an antibonding

27

species are

n-orbital

Atomic Radii as Function of Atomic Number

In addition

to the factors discussed above, the radii of the atoms also In Figure 2-3, play an important role in determining chemical structures.

the various kinds of atomic radii are plotted as a function of atomic number for the elements in the first three rows of the periodic table. In this graph,

the closest-packing radii of the inert-gas atoms are denoted by a star. It is seen that the a-bond radii decrease appreciably when going from the left to the right in each row of the periodic table, and, as might be expected, the

i/t.

75.2 + 2.2

P-H bond energy in phosphine

such as the

energies,

-

29

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