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]

No elements in this region have been synthesized or discovered in nature. (Element 122 was claimed to exist naturally in April 2008, but this claim was widely believed to be erroneous.)[2] 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. If period 9 does exist, it is likely to be the last.

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.[3]

Contents

Extended periodic table, including the g-block

Extended Periodic Table[4]
(Superheavy elements may not follow the order of this table)
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.

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 corresponds to the assumption that the Madelung rule will continue to hold at higher atomic number; 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; for example, calculations suggest that it may be elements 165 and 166 which occupy the 9s block (leaving the 8p orbital incomplete) assuming they are physically possible.[5]

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 173,[6] 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,[7] which is expected to center around Z = 126.[8]

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

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.[9] 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.[10] Richard Feynman pointed out this effect, so the last element expected under this model, 137 (untriseptium), is sometimes called feynmanium.

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 (unseptrium), such that non-ionized atoms may be limited to elements equal to or lower than this.[6]

See also

References

  1. ↑ [1]
  2. ↑ "Heaviest element claim criticised". Rsc.org. 2008-05-02. http://www.rsc.org/chemistryworld/News/2008/May/02050802.asp. Retrieved 2010-03-16. 
  3. ↑ For example, an element in the column labeled g1 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.
  4. ↑ The labels "g1", etc. are inspired by the Madelung rule, but this is merely an empirical rule, with well-known exceptions such as copper.
  5. ↑ Pekka Pyykkö, Peter Schwerdtfeger (2004), Relativistic electronic structure theory, p 23.
  6. ↑ 6.0 6.1 Walter Greiner and Stefan Schramm (2008). American Journal of Physics 76: 509. doi:10.1119/1.2820395. , and references therein.
  7. ↑ Encyclopædia Britannica. "transuranium element (chemical element) - Britannica Online Encyclopedia". Britannica.com. http://www.britannica.com/EBchecked/topic/603220/transuranium-element. Retrieved 2010-03-16. 
  8. ↑ S. Cwiok, P.-H. Heenen and W. Nazarewicz (2005). "Shape coexistence and triaxiality in the superheavy nuclei". Nature 433: 705.
  9. ↑ See for example R. Eisberg and R. Resnick, Quantum Physics of Atoms, Molecules, Solids, Nuclei and Particles, Wiley (New York: 1985).
  10. ↑ James D. Bjorken and Sidney D. Drell, Relativistic Quantum Mechanics, McGraw-Hill (New York:1964).

External links

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