Extended periodic table

There are currently seven periods in the periodic table of chemical elements, culminating with atomic number 118. If further elements with higher atomic numbers than this are discovered, they will be placed in additional periods, laid out (as with the existing periods) to illustrate periodically recurring trends in the properties of the elements concerned. Any additional periods are expected to contain a larger number of elements than the seventh period, as they are calculated to have an additional so-called g-block, containing 18 elements with partially filled g-orbitals in each period. An eight-period table containing this block was suggested by Glenn T. Seaborg in 1969.^[1][2]

No elements in this region have been synthesized or discovered in nature.^[3] The first element of the g-block may have atomic number 121, and thus would have the systematic name unbiunium. Elements in this region are likely to be highly unstable with respect to radioactive decay, and have extremely short half lives, although element 126 is hypothesized to be within an island of stability that is resistant to fission but not to alpha decay. It is not clear how many elements beyond the expected island of stability are physically possible, if period 8 is complete, or if there is a period 9.

According to the orbital approximation in quantum mechanical descriptions of atomic structure, the g-block would correspond to elements with partially-filled g-orbitals. However, spin-orbit coupling effects reduce the validity of the orbital approximation substantially for elements of high atomic number.^[4]

Extended periodic table, including the g-block

It is unknown how far the periodic table might extend beyond the known 118 elements. Glenn T. Seaborg suggested that the highest possible element may be under Z=130.^[5] However, if higher elements do exist, it is unlikely that they can be meaningfully assigned to the periodic table above approximately Z=173, as discussed in the next section. This chart therefore ends at that number, without meaning to imply that all of those 173 elements are actually possible, nor to imply that heavier elements are not possible. (See also extended periodic table (large version).)

Extended Periodic Table
(Superheavy elements may not exist, and may not follow the order of this table even if they do)

1

1 H

2 He

2

3 Li

4 Be

5 B

6 C

7 N

8 O

9 F

10 Ne

3

11 Na

12 Mg

13 Al

14 Si

15 P

16 S

17 Cl

18 Ar

4

19 K

20 Ca

21 Sc

22 Ti

23 V

24 Cr

25 Mn

26 Fe

27 Co

28 Ni

29 Cu

30 Zn

31 Ga

32 Ge

33 As

34 Se

35 Br

36 Kr

5

37 Rb

38 Sr

39 Y

40 Zr

41 Nb

42 Mo

43 Tc

44 Ru

45 Rh

46 Pd

47 Ag

48 Cd

49 In

50 Sn

51 Sb

52 Te

53 I

54 Xe

6

55 Cs

56 Ba

57 La

58 Ce

59 Pr

60 Nd

61 Pm

62 Sm

63 Eu

64 Gd

65 Tb

66 Dy

67 Ho

68 Er

69 Tm

70 Yb

71 Lu

72 Hf

73 Ta

74 W

75 Re

76 Os

77 Ir

78 Pt

79 Au

80 Hg

81 Tl

82 Pb

83 Bi

84 Po

85 At

86 Rn

7

87 Fr

88 Ra

89 Ac

90 Th

91 Pa

92 U

93 Np

94 Pu

95 Am

96 Cm

97 Bk

98 Cf

99 Es

100 Fm

101 Md

102 No

103 Lr

104 Rf

105 Db

106 Sg

107 Bh

108 Hs

109 Mt

110 Ds

111 Rg

112 Cn

113 Uut

114 Uuq

115 Uup

116 Uuh

117 Uus

118 Uuo

8

119 Uue

120 Ubn

121 Ubu

122 Ubb

123 Ubt

124 Ubq

125 Ubp

126 Ubh

127 Ubs

128 Ubo

129 Ube

130 Utn

131 Utu

132 Utb

133 Utt

134 Utq

135 Utp

136 Uth

137 Uts

138 Uto

139 Ute

140 Uqn

141 Uqu

142 Uqb

143 Uqt

144 Uqq

145 Uqp

146 Uqh

147 Uqs

148 Uqo

149 Uqe

150 Upn

151 Upu

152 Upb

153 Upt

154 Upq

155 Upp

156 Uph

157 Ups

158 Upo

159 Upe

160 Uhn

161 Uhu

162 Uhb

163 Uht

164 Uhq

165 Uhp

166 Uhh

167 Uhs

168 Uho

9

169 Uhe

170 Usn

171 Usu

172 Usb

173 Ust

Blocks of the periodic table

s-block

p-block

d-block

f-block

g-block

(Undiscovered (theorized) elements are coloured in a lighter shade)

All of these hypothetical undiscovered elements are named by the International Union of Pure and Applied Chemistry (IUPAC) systematic element name standard which creates a generic name for use until the element has been discovered, confirmed, and an official name approved.

As of April 2011^[update], synthesis has been attempted for only ununennium, unbinilium, unbibium, unbiquadium and unbihexium. (Z = 119, 120, 122, 124 and 126)

The positioning of the g-block in the table (to the left of the f-block, to the right, or in between) is speculative. The positions shown in the table above correspond to the assumption that the Madelung rule will continue to hold for higher atomic numbers; this assumption may or may not be true. At element 118, the orbitals 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, 5s, 5p, 5d, 5f, 6s, 6p, 6d, 7s and 7p are assumed to be filled, with the remaining orbitals unfilled. The orbitals of the eighth period are predicted to be filled in the order 8s, 5g, 6f, 7d, 8p. However, after approximately element 120, the proximity of the electron shells makes placement in a simple table problematic.

Pyykkö model

Not all models show the higher elements following the pattern established by lighter elements. Pekka Pyykkö, for example, used computer modeling to calculate the positions of elements up to Z=172, and found that several were displaced from the Madelung energy-ordering rule.^[6] He predicts that the orbital shells will fill up in this order:

• 8s,
• 5g,
• the first two spaces of 8p,
• 6f,
• 7d,
• 9s,
• the first two spaces of 9p,
• the rest of 8p.

He also suggests that period 8 be split into three parts:

• 8a, containing 8s,
• 8b, containing the first two elements of 8p,
• 8c, containing 7d and the rest of 8p.^[7]

Pyykkö model. Displaced elements are in boldface.

8

119 Uue

120 Ubn

121 Ubu

122 Ubb

123 Ubt

124 Ubq

125 Ubp

126 Ubh

127 Ubs

128 Ubo

129 Ube

130 Utn

131 Utu

132 Utb

133 Utt

134 Utq

135 Utp

136 Uth

137 Uts

138 Uto

141 Uqu

142 Uqb

143 Uqt

144 Uqq

145 Uqp

146 Uqh

147 Uqs

148 Uqo

149 Uqe

150 Upn

151 Upu

152 Upb

153 Upt

154 Upq

155 Upp

156 Uph

157 Ups

158 Upo

159 Upe

160 Uhn

161 Uhu

162 Uhb

163 Uht

164 Uhq

139 Ute

140 Uqn

169 Uhe

170 Usn

171 Usu

172 Usb

9

165 Uhp

166 Uhh

167 Uhs

168 Uho

End of the periodic table

The number of physically possible elements is unknown. The light-speed limit on electrons orbiting in ever-bigger electron shells theoretically limits neutral atoms to a Z of approximately 137,^[8] after which it would be nonsensical to assign the elements to blocks on the basis of electron configuration. However, it is likely that the periodic table actually ends much earlier, possibly soon after the island of stability,^[5] which is expected to center around Z = 126.^[9]

Additionally the extension of the periodic and nuclides tables is restricted by the proton and the neutron drip lines.

Bohr model breakdown

The Bohr model exhibits difficulty for atoms with atomic number greater than 137, for the speed of an electron in a 1s electron orbital, v, is given by

$v = Z \alpha c \approx \frac{Z c}{137.036}$

where Z is the atomic number, and α is the fine structure constant, a measure of the strength of electromagnetic interactions.^[10] Under this approximation, any element with an atomic number of greater than 137 would require 1s electrons to be traveling swifter than c, the speed of light. Hence a non-relativistic model such as the Bohr model is inadequate for such calculations.

The Dirac equation

The semi-relativistic Dirac equation also has problems for Z > 137, for the ground state energy is

$E=m_0 c^2 \sqrt{1-Z^2 \alpha^2}$

where m₀ is the rest mass of the electron. For Z > 137, the wave function of the Dirac ground state is oscillatory, rather than bound, and there is no gap between the positive and negative energy spectra, as in the Klein paradox.^[11] Richard Feynman pointed out this effect, so the last element expected under this model, 137 (untriseptium), is sometimes called feynmanium (symbol: Fy).

However, a realistic calculation has to take into account the finite extension of the nuclear-charge distribution. This results in a critical Z of ≈ 173 (unsepttrium), such that neutral atoms may be limited to elements equal to or lower than this.^[8] Higher elements could only exist as ions, for example as salts.

See also

• Electron configuration
• Nuclear shell model
• Table of nuclides (combined)
• Period 8 element

References

1. ^ Seaborg, Glenn (August 26, 1996). "An Early History of LBNL". http://www.lbl.gov/LBL-PID/Nobelists/Seaborg/65th-anniv/29.html. 
2. ^ Frazier, K. (1978). "Superheavy Elements". Science News 113 (15): 236–238. doi:10.2307/3963006. JSTOR 3963006. 
3. ^ Element 122 was claimed to exist naturally in April 2008, but this claim was widely believed to be erroneous. "Heaviest element claim criticised". Rsc.org. 2008-05-02. http://www.rsc.org/chemistryworld/News/2008/May/02050802.asp. Retrieved 2010-03-16. 
4. ^ For example, an element in the column g¹ (Ubu and Usu) may indeed have exactly one valence-shell g-electron (as the name suggests), but it is also possible that it would have more, or none at all.
5. ^ ^{a b} Seaborg (ca. 2006). "transuranium element (chemical element)". Encyclopædia Britannica. http://www.britannica.com/EBchecked/topic/603220/transuranium-element. Retrieved 2010-03-16. 
6. ^ "Extended elements: new periodic table". 2010. http://www.rsc.org/Publishing/ChemScience/Volume/2010/11/Extended_elements.asp. 
7. ^ Pyykkö, Pekka (2011). "A suggested periodic table up to Z≤ 172, based on Dirac–Fock calculations on atoms and ions". Physical Chemistry Chemical Physics 13 (1): 161–8. Bibcode 2011PCCP...13..161P. doi:10.1039/c0cp01575j. PMID 20967377. 
8. ^ ^{a b} Walter Greiner and Stefan Schramm (2008). "Resource Letter QEDV-1: The QED vacuum". American Journal of Physics 76 (6): 509. Bibcode 2008AmJPh..76..509G. doi:10.1119/1.2820395. , and references therein.
9. ^ Cwiok, S.; Heenen, P.-H.; Nazarewicz, W. (2005). "Shape coexistence and triaxiality in the superheavy nuclei". Nature 433 (7027): 705. Bibcode 2005Natur.433..705C. doi:10.1038/nature03336. PMID 15716943. 
10. ^ See for example Eisberg, R.; Resnick, R. (1985). Quantum Physics of Atoms, Molecules, Solids, Nuclei and Particles. New York: Wiley. ISBN 047187373X. 
11. ^ Bjorken, James D.; Drell, Sidney D. (1964). Relativistic Quantum Mechanics. New York: McGraw-Hill. ISBN 0070054932. 

External links

• Holler, Jim. "Images of g-orbitals". University of Kentucky. http://www.uky.edu/~holler/html/g.html. 
• Rihani, Jeries A.. "The extended periodic table of the elements". http://jeries.rihani.com. 
• Scerri, Eric (2007). The Periodic Table, Its Story and Its Significance. Oxford University Press. ISBN 0195305736. 
• Chart of the Nuclides (17th ed.). Knolls Atomic Power Laboratory. 2010. ISBN 978-0984365302. http://www.nuclidechart.com/.