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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 were to be discovered, they would be placed in an eighth, and possibly ninth, period. The 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 this 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.

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]

[edit] Extended periodic table, including the g-block

**Extended Periodic Table**^[4]
(Superheavy elements may not follow the order of this table)
	s¹	s²																																											p¹	p²	p³	p⁴	p⁵	p⁶
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																																	d¹	d²	d³	d⁴	d⁵	d⁶	d⁷	d⁸	d⁹	d¹⁰	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																			f¹	f²	f³	f⁴	f⁵	f⁶	f⁷	f⁸	f⁹	f¹⁰	f¹¹	f¹²	f¹³	f¹⁴	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	g¹	g²	g³	g⁴	g⁵	g⁶	g⁷	g⁸	g⁹	g¹⁰	g¹¹	g¹²	g¹³	g¹⁴	g¹⁵	g¹⁶	g¹⁷	g¹⁸	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 Uub	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	174 Usq	175 Usp	176 Ush	177 Uss	178 Uso	179 Use	180 Uon	181 Uou	182 Uob	183 Uot	184 Uoq	185 Uop	186 Uoh	187 Uos	188 Uoo	189 Uoe	190 Uen	191 Ueu	192 Ueb	193 Uet	194 Ueq	195 Uep	196 Ueh	197 Ues	198 Ueo	199 Uee	200 Bnn	201 Bnu	202 Bnb	203 Bnt	204 Bnq	205 Bnp	206 Bnh	207 Bns	208 Bno	209 Bne	210 Bun

Blocks of the periodic table

s-block

p-block

d-block

f-block

g-block

ion

(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 122, 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]

[edit] 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, while similar considerations of the nucleus limit ions to a Z of approximately 210.^{[citation needed]} (This range is grey and in italics in the table.) However, it is likely that the periodic table actually ends much earlier, possibly soon after the island of stability,^[7]^{[better ref needed]} which is expected to center around Z = 126.^[8]

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

[edit] 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.

[edit] The Dirac equation

The semirelativistic 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]

[edit] See also

[edit] References

^ http://acs.lbl.gov/Seaborg.talks/65th-anniv/29.html
^ Heaviest element claim criticised
^ 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.
^ The labels "g¹", etc. are inspired by the Madelung rule, but this is merely an empirical rule, with well-known exceptions such as copper.
^ Pekka Pyykkö, Peter Schwerdtfeger (2004), Relativistic electronic structure theory, p 23.
^ ^a ^b Walter Greiner and Stefan Schramm, Am. J. Phys. 76, 509 (2008), and references therein.
^ http://www.britannica.com/EBchecked/topic/603220/transuranium-element
^ S. Cwiok, P.-H. Heenen and W. Nazarewicz (2005). "Shape coexistence and triaxiality in the superheavy nuclei". Nature 433: 705.
^ See for example R. Eisberg and R. Resnick, Quantum Physics of Atoms, Molecules, Solids, Nuclei and Particles, Wiley (New York: 1985).
^ James D. Bjorken and Sidney D. Drell, Relativistic Quantum Mechanics, McGraw-Hill (New York:1964).

http://www.springerlink.com/content/j303171428652143/

[edit] External links

Images of g-orbitals from the University of Kentucky
jeries.rihani.com - The extended periodic table of the elements.

[0] ttp://acs.lbl.gov/Seaborg.talks/65th-anniv/29.html

[1] Heaviest element claim criticised

[2] 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.

[3] The labels "g¹", etc. are inspired by the Madelung rule, but this is merely an empirical rule, with well-known exceptions such as copper.

[4] Pekka Pyykkö, Peter Schwerdtfeger (2004), Relativistic electronic structure theory, p 23.

[Greiner-5] Walter Greiner and Stefan Schramm, Am. J. Phys. 76, 509 (2008), and references therein.

[6] ttp://www.britannica.com/EBchecked/topic/603220/transuranium-element

[7] S. Cwiok, P.-H. Heenen and W. Nazarewicz (2005). "Shape coexistence and triaxiality in the superheavy nuclei". Nature 433: 705.

[8] See for example R. Eisberg and R. Resnick, Quantum Physics of Atoms, Molecules, Solids, Nuclei and Particles, Wiley (New York: 1985).

[9] James D. Bjorken and Sidney D. Drell, Relativistic Quantum Mechanics, McGraw-Hill (New York:1964).

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