IMPORTACION SIN ESTAR INSCRITOS EN EL PADRÒN

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

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 thanc, 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 pr oblems for Z > 137, for the ground state energy is

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

• Electron configuration

• Nuclear shell model

• Table of nuclides (combined)

References

[1] (http://acs.lbl.gov/Seaborg.talks/65th-anniv/29.html)

[2] "Heaviest element claim criticised" (http://www.rsc.org/chemistryworld/News/2008/May/02050802.asp). Rsc.org. 2008-05-02. . Retrieved 2010-03-16.

[3] For example, an element in the column labeledg¹may 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] Walter Greiner and Stefan Schramm (2008). American Journal of Physics76: 509. doi:10.1119/1.2820395., and references therein.

[7] Encyclopædia Britannica. "transuranium element (chemical element) - Britannica Online Encyclopedia" (http://www.britannica.com/ 

EBchecked/topic/603220/transuranium-element). Britannica.com. . Retrieved 2010-03-16.

[8] S. Cwiok, P.-H. Heenen and W. Nazarewicz (2005). "Shape coexistence and triaxiality in the superheavy nuclei". Nature433: 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).

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

External links

• Images of g-orbitals (http://www.uky.edu/~holler/html/g.html) from the University of Kentucky

• jeries.rihani.com (http://jeries.rihani.com) - The extended periodic table of the elements.

• Eric Scerri, The Periodic Table, Its Story and Its Significance, Oxford University Press, 2007.

Blocks

Block

A block of the periodic table of elements is a set of adjacent groups. The term appears to have been first used (in French) by Charles Janet. ^[1]The respective highest-energy electrons in each element in a block belong to the same atomic orbital type. Each block is named after its characteristic orbital; thus, the blocks are:

• s-block  

• p-block  

• d-block  

• f-block  

• g-block (hypothetical)

The block names (s, p, d, f. and g) are derived from the quality of the spectroscopic lines of the associated atomic orbitals:sharp,principal,diffuse andf undamental, the rest being named in alphabetical order. Blocks are sometimes called families.

[1] Charles Janet, La classification helicoidal des elements chimiques, Beauvais, 1928

s-block

Chemical elements in s-block

Group 1 2 18 Period

1 1

H

2 He

2 3

Li 4 Be

3 11

Na 12 Mg

4 19

K 20 Ca

5 37

Rb 38 Sr

6 55

Cs 56 Ba

7 87

Fr 88 Ra

The s-block of the periodic table of elements consists of the first two groups: the alkali metals and alkaline earth metals, plus hydrogen and helium.

These elements are distinguished by the property that in the atomic ground state, the highest-energy electron is in an s-orbital. Except in hydrogen and helium, these electrons are very easily lost to form positive ions. The helium

configuration is chemically exceedingly stable and thus helium has

configuration is chemically exceedingly stable and thus helium hasno known stable compoundsno known stable compounds; thus it is generally; thus it is generally grouped with the noble gases.

grouped with the noble gases.

The other elements of the s-block are all extremely powerful reducing agents, so much so that they

The other elements of the s-block are all extremely powerful reducing agents, so much so that they never never occuroccur naturally in the free state. The met

naturally in the free state. The metallic formallic forms of these eles of these elements canments can onlyonly be extrbe extracted by electrolysis of a moltacted by electrolysis of a molten salt,en salt, since water is much more easily reduced to hydrogen than the ions of these metals. Sir Humphry Davy, in 1807 and since water is much more easily reduced to hydrogen than the ions of these metals. Sir Humphry Davy, in 1807 and 1808, was the first to isolate all of these metals except lithium, beryllium, rubidium and caesium. Beryllium was 1808, was the first to isolate all of these metals except lithium, beryllium, rubidium and caesium. Beryllium was isolated independently by F. Wooler and A.A. Bussy in 1828, while lithium was isolated by Robert Bunsen in 1854, isolated independently by F. Wooler and A.A. Bussy in 1828, while lithium was isolated by Robert Bunsen in 1854, who isolated rubidium nine years later after having observed it and caesium spectroscopically. Caesium was not who isolated rubidium nine years later after having observed it and caesium spectroscopically. Caesium was not isolated until 1881 when Carl Setterberg electrolysed the molten cyanide.

isolated until 1881 when Carl Setterberg electrolysed the molten cyanide.

The s-block metals vary from extremely soft (all the alkali metals) to quite hard (beryllium). With the exception of  The s-block metals vary from extremely soft (all the alkali metals) to quite hard (beryllium). With the exception of  beryllium and magnesium, the metals are too reactive for any structural use except as very minor components (<2%) beryllium and magnesium, the metals are too reactive for any structural use except as very minor components (<2%) of alloys with lead. Beryllium

of alloys with lead. Beryllium and magnesium, though very expensive, are valuable for and magnesium, though very expensive, are valuable for uses that require strength anduses that require strength and lightness. They are extremely valuable as reducing agents to extract titanium, zirconium, thorium and tantalum from lightness. They are extremely valuable as reducing agents to extract titanium, zirconium, thorium and tantalum from their ores, and have other uses as reducing agents in organic chemistry.

their ores, and have other uses as reducing agents in organic chemistry.

All the s-block metals are dangerous fire hazards which require special extinguishants to extinguish, except for All the s-block metals are dangerous fire hazards which require special extinguishants to extinguish, except for beryllium and magnesium, storage must be under either argon or an inert liquid hydrocarbon. They react vigorously beryllium and magnesium, storage must be under either argon or an inert liquid hydrocarbon. They react vigorously with water to liberate hydrogen, except for magnesium, which reacts slowly, and beryllium, which reacts only when with water to liberate hydrogen, except for magnesium, which reacts slowly, and beryllium, which reacts only when amalgamated with mercury to destroy the oxide film. Lithium has similar properties to magnesium due to the amalgamated with mercury to destroy the oxide film. Lithium has similar properties to magnesium due to the diagonal relationship with magnesium in the periodic table.

diagonal relationship with magnesium in the periodic table.