Extended periodic table


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]

Contents

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

(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, 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

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. 

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