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3.1.2 Properties of the elements

Symbols, atomic weights, atomic numbers, densities, melting points and boiling points (pressure 101.325 kN m−2) of the elements

The values of the relative atomic masses (Ar(E)), scaled to the relative mass Ar(12C) = 12, are those recommended in the 1991 Report by the International Union of Pure and Applied Chemistry Commission on Atomic Weights (IUPAC, 1992). The regular biennial reviews by the Commission rely on significant improvements in the precision of mass measurement and refined assessment of isotopic composition of terrestrial materials. (Separate tables of information on the composition and relative mass for extra-terrestrial sources are presented in the Commission Reports.)

In the following table of the elements, arranged in alphabetical order, uncertainty in the last reported digit is expressed as ‘± n’. Precision has improved significantly in the past 15 years. The biennial reports for 1979 to 1991 present one or more improvements for 66 elements, and although the uncertainty still remains in excess of 0.01% for 24 elements, many of these suffer from variable isotopic composition. Typical improvements recorded in the 1989 report (IUPAC, 1991) include tightening the Ar of Ni from 58.69 to 58.6934 ± 2 and of Sb from 121.75 to 121.757 ± 3, while better knowledge of isotopic composition reduced the uncertainty for Hg so that Ar became 200.59 ± 2, and 231Pa was fixed at 231.035 88 ± 2. The 1991 report (IUPAC, 1992) took advantage of higher precision mass measurement to tighten In to 114.818 ± 3, W to 183.84 ±1 and Os to 190.23 ± 3. The footnote symbol ‘g’, which reflects the detection of variable abundance in some terrestrial geological specimens (see the notes at the foot of the table), was added for C and K. The footnotes to this table elaborate the types of variations to be expected for individual elements. The values of Ar(E) given here apply to elements as they exist naturally on earth. When used with due regard to the footnotes they are considered reliable to ± 1 in the last digit unless otherwise noted. An element with an asterisk has no stable isotope and lacks a characteristic terrestrial isotopic composition. A value in parenthesis is the atomic weight of the isotope of the radionuclide of that element which is believed to be the most frequently found and which has the longest half-life.

For a discussion of the arrangement of electrons in atoms, and a table (in atomic number order) of the electron configuration of elements for the ground state of neutral atoms, see Section 4.1.1. For a table listing one or more ionisation potentials for elements from Hydrogen to Lanthanum (Z = 57) and some commoner atoms of higher Z, see Section 4.1.2.



Element

Symbol

Atomic
No.

Atomic
weight

Density

ρ/(kg m−3)

Melting point

θ/°C

Boiling point

θ/°C

 

 

     

 

 

Actinium* 

     Ac

89

(227.027 8)         

10 060  

1050       

3200

Aluminium

     Al

13

   26.981 539 ± 5

2 698

  660.323

2520

Americium*

     Am

95

(243.061 4)        

13 670  

1176      

2600

Antimony

     Sb

51

121.757 ± 3     

6 692

 630.63

1587

Argon

     Ar

18

39.948g, r    

1656/ − 233 °C

–189.34

        –185.856

Arsenic

     As

33

 74.921 59 ± 2

5 776

610 solid sublimes      

Astatine*

     At

85

(209.987 1)        

 

300 

  350

Barium

     Ba

56

137.327 ± 7g    

3 594

728 

1900

Berkelium*

     Bk

97

(247.070 3)         

14 790  

1050   

 

Beryllium

     Be

  4

    9.012 182 ± 3

1 846

1287   

2470

Bismuth

     Bi

83

208.980 37 ± 3  

9 803

     271.442

1560

Boron

     B

  5

 10.811 ± 5m, r 

2 466

2075 

4000

Bromine

     Br

35

79.904          

3 120

    –7.3

       58.9

Cadmium

     Cd

48

112.411 ± 8g     

8 647

      321.08

  770

Caesium

     Cs

55

 132.905 43 ± 5   

1 900

     28.4

  670

Calcium

     Ca

20

 40.078 ± 4g     

1 530

 840

1484

Californium*

     Cf

98

(251.079 6)         

 

 900

 

Carbon

     C

  6

12.011g.r        

  2 266

4490

 

Cerium

     Ce

58

140.115 ± 4       

  6 711

  800

3420

Chlorine

     Cl

17

35.4527 ± 9   

2030/−160 °C

 −101

     –34.0

Chromium

     Cr

24

51.996 ± 6    

  7 194

 1907

2670

Cobalt

     Co

27

    58.933 20 ± 1    

  8 800

  1495

2930

Copper

     Cu

29

 63.546 ± 3r     

  8 933

      1084.62

2560

Curium*

     Cm

96

(247.070 3)         

13 300

1345

 

Dysprosium

     Dy

66

162.50 ± 3        

  8 531

1410

2560

Einsteinium*

     Es

99

(252.081 6)         

 

  860

 

Erbium

     Er

68

167.26 ± 3g       

  9 044

1530

2860

Europium

     Eu

63

151.965 ± 9       

  5 248

  822

1600

Fermium*

     Fm

100  

(257.095 1)          

 

1530

 

Fluorine

     F

  9

    18.998 403 2 ± 9  

1140/−200 °C

  −219.6

   –188.1

Francium*

     Fr

87

(223.018 5)          

 

   27

  650

Gadolinium

     Gd

64

157.25 ± 3g          

  7 870

1314

3260

Gallium

     Ga

31

69.723 ± 1      

  5 905

         29.76

2200

Germanium

     Ge

32

72.61 ± 2        

  5 323

  938

2830

Gold  

     Au

79

     196.966 54 ± 3      

19 281

      1064.18

2850

Hafnium

     Hf

72

178.49 ± 2       

13 276

2230

4600

Helium

     He

  2

        4.002 602 ± 2g, r

120/4.22 K

        3–5 K

               4.22 K

Holmium

     Ho

67

     164.930 32 ± 3      

  8 797

1470

2700

Hydrogen

     H

  1

          1.00794 ± 7g, m, r

89/- 266.8 °C

     − 259.35

      - 252.87

Indium

     In

49

114.818 ± 3      

  7 290

           156.599

2070

Iodine

     I

53

126.904 47 ± 3 

  4 953

      113.6

  184

Iridium

     Ir

77

192.22 ± 3        

22 550

  2447

4430

Iron

     Fe

26

     55.847 ± 3         

  7 873

1540

2860

Krypton

     Kr

36

83.80 ± 1g, m 

3000/−188 °C

   −157.3

   –153.2

Lanthanum

     La

57

138.905 5 ± 2g   

  6 174

  920

3460

Lawrencium*

     Lr

103  

(260.105 4)         

 

1630

 

Lead

     Pb

82

207.2 ± 1g, r        

11 343

           327.502

1750

Lithium

     Li

  3

       6.941 ± 2 g, m, r

     533

     180.5

1340

Lutetium

     Lu

71

174.967 ± 1     

  9 842

1660

3390

Magnesium

     Mg

12

24.305 0 ± 6 

  1 738

  650

1090

Manganese

     Mn

25

 54.938 05 ± 1

  7 473

1250

2060

Mendelevium*

     Md

101  

(258.098 6)      

 

  830

 

Mercury

     Hg

80

200.59 ± 2     

13 546

         −38.834

        356.73

Molybdenum

     Mo

42

95.94 ± 1   

10 222

 2623

4640

Neodymium

     Nd

60

144.24 ± 3g       

  7 000

1016

3070

Neon

     Ne

10

      20.179 7 ± 6g, m

1442/−268 °C

     −248.59

      −246.08

Neptunium*

     Np

93

(237.048 2)      

20 450

  640

3900

Nickel

     Ni

28

  58.693 4 ± 2

  8 907

 1455

2990

Niobium

     Nb

41

    92.906 38 ± 2

  8 578

 2477

4700

Nitrogen

     N

  7

     14.006 74 ± 7g

1035/−268.8 °C

−210

       −195.80

Nobelium*

     No

102  

(259.100 9)     

 

  830

 

Osmium

     Os

76

190.23 ± 3g  

22 580

3030

5000

Oxygen

     O

  8

      15.999 4 ± 3g, r

1460/−252.7 °C

     − 218.79

      −182.96

Palladium

     Pd

46

106.42 ± 1g  

11 995

 1555

2960

Phosphorus

     P

15

      30.973 762 ± 4

1820 (yellow)

44.2 (yellow)

  277

Platinum

     Pt

78

195.08 ± 3   

21 450

1768

3820

Plutonium*

     Pu

94

(244.064 2)     

19 814

 640

3230

Polonium*

     Po

84

(208.982 4)     

  9 400

  254

  960

Potassium

     K

19

 39.098 3 ± 1

     862

       63.4

  760

Praseodymium

     Pr

59

 140.907 65 ± 3

  6 779

  931

3510

Promethium*

     Pm

61

(144.912 7)      

    7 220§

  1142§

  3300§

Protoactinium*

     Pa

91

 (231.035 88 ± 2)

15 370

1570

4000

Radium*

     Ra

88

  (226.025 4)        

  5 000

  700

1500

Radon*

     Rn

86

(222.017 6)      

440 (liquid

  −71

  −62

 

 

 

 

–62 °C)

 

 

Rhenium

     Re

75

186.207 ± 1     

21 023

3186

5600

Rhodium

     Rh

45

102.905 50 ± 3

12 420

 1963

3700

Rubidium

     Rb

37

  85.467 8 ± 3g

  1 533

       39.3

  690

Ruthenium

     Ru

44

101.07 ± 2g     

12 360

2330

4150

Samarium

     Sm

62

150.36 ± 3g     

  7 536

1170

1790

Scandium

     Sc

21

    44.955 910 ± 9

  2 992

1540

2830

Selenium

     Se

34

 78.96 ± 3     

  4 808

  220

  685

Silicon

     Si

14

 28.085 5 ± 3

  2 329

1410

3260

Silver

     Ag

47

 107.868 2 ± 2g

10 500

         961.78

2160

Sodium

     Na

11

      22.989 768 ± 6

     966

       97.7

  880

Strontium

     Sr

38

87.62 ± 1g

  2 583

  777

1380

Sulphur

     S

16

32.066 ± 6r

  2 086

       115.32

         444.674

Tantalum

     Ta

73

180.947 9 ± 1

16 670

3020

5560

Technetium*

     Tc

43

(97.907 2)    

11 496

2160

4260

Tellurium

     Te

52

127.60 ± 3g  

  6 247

  450

  990

Terbium

     Tb

65

  158.925 34 ± 3

  8 267

1360

3220

Thallium

     Tl

81

204.383 3 ± 2

11 871

  304

1470

Thorium*

     Th

90

    232.038 1 ± 1g, x

11 725

1750

4790

Thulium

     Tm

69

  168.934 21 ± 3

  9 325

1550

1950

Tin

     Sn

50

118.710 ± 7  

  7 285

           231.928

2620

Titanium

     Ti

22

47.88 ± 3 

  4 508

1670

3290

Tungsten

     W

74

183.84 ± 1   

19 254

  3422

5550

Uranium*

     U

92

         238.028 9 ± 1g, m, y

19 050

1135

4130

Vanadium

     V

23

   50.941 5 ± 1

  6 090

1920

3400

Xenon

     Xe

54

  131.29 ± 2g, m

3560/(−185 °C)

    −111.8

   −108.1

Ytterbium

     Yb

70

 173.04 ± 3    

  6 966

   824

1200

Yttrium

     Y

39

       88.905 85 ± 2g

  4 475

 1525

3340

Zinc

     Zn

30

65.39 ± 2

  7 135

            419.527

  910

Zirconium

     Zr

40

   91.224 ± 2g

  6 507

 1850

4400

 

 

 

 

 

 

 


Notes:

The IUPAC Commission on Nomenclature of Inorganic Chemistry (CNIC) provisional scheme (1978) of numerical names for elements 104–107 (e.g. Un-nil-quadium for 104) has not been generally popular. At its meeting in July 1994, CNIC proposed a sequence of names for elements 104–109 which was confirmed by the IUPAC Bureau in September. This CNIC set directly conflicted with the choice of names proposed by various discoverers of these artificial elements at the JINR Dubna (Moscow), GSI Darmstadt and Lawrence Berkeley (California) national laboratories and approved in March 1994 by the American Chemical Society (ACS). The final decision to uphold CNIC set (Dubnium, Joliotium, Rutherfordium, Bohrium, Hahnium and Meitnerium respectively) or compromise with the ACS set (Rutherfordium, Hahnium, Seaborgium, Neilsbohrium, Hassium and Meitnerium) has been deferred by IUPAC Council until 1997.

g

 

Geologically exceptional specimens are known in which the element has an isotopic composition outside the limits for normal material. The difference between the atomic weight of the element in such specimens and that given in the table may considerably exceed the implied uncertainty.

m

 

Modified isotopic compositions may be found in commercially available material because it has been subjected to an undisclosed or inadvertent isotopic separation. Substantial deviations in atomic weight of the element from that given in the table can occur.

r

 

Range in isotopic composition of normal terrestrial material prevents a more precise atomic weight being given; the tabulated A(E) value should be applicable to any normal material.

x

 

Thorium has a well defined (mononuclide) composition in minerals with only rare exceptions. In certain places, however (most notably in ocean water), measurable quantities of 230Th (Ionium) can be found.

y

 

Uranium is the only element with no stable isotopes but which has a characteristic terrestrial composition of long-lived isotopes such that a meaningful atomic weight can be given for natural samples: 238U = 238.050 8.

 

Primary and secondary fixed points on the International Practical Temperature Scale of 1990.

 

This and other values marked K are in kelvins.

§

 

This property refers to 147Pm.




References


IUPAC (1991) Pure & Appl. Chem., 63, 976–1002.
IUPAC (1992) Pure & Appl. Chem., 64, 1519–1534.




G.F.Phillips


 

 

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