Super-átomos Uma tabela periódica tridimensional?

Prof. Dr. Arnaldo Dal Pino JúniorDep. de Física do ITA

Lavoisier divided the few elements known in the 1700's into classes.

John DaltonThe mass of an atom was it's most important property

"The chemical elements are composed of... indivisible particles of matter, called atoms... atoms of the same element are identical in all respects, particularly weight." - Dalton

Fósforo (P).

Primeiro elemento a ser descoberto.

Ponto de partida para a construção

da tabela periódica".

Cloro, bromo e iôdo;

A tríade da primeira

tentativa.

Periodic table begins with German chemist Johann Dobereiner (1780-1849) who grouped elements based on similarities.

Dobereiner noticed the atomic weight of strontium fell midway between the weights of calcium and barium: Ca Sr Ba (40 + 137) ÷ 2 = 88

coincidence? Dobereiner noticed the same pattern for the alkali metal triad (Li/Na/K) and the halogen triad (Cl/Br/I).

Li Na K Cl Br I 7 23 39 35 80 127

In 1829 Dobereiner proposed the Law of Triads: Middle element in the triad had atomic weight that was the average of the othertwo members.

Soon other scientists found chemical relationships extended beyond triads. Fluorine was added to Cl/Br/I group; sulfur, oxygen, selenium and tellurium were grouped into a family; nitrogen, phosphorus, arsenic, antimony, and bismuth were classified as another group

Alexandre Beguyer de Chancourtois (1820-1886)

professor of geology at the School of Mines in Paris recognized periodicity in the physical properties of the elements.

1862 list of all the known elements.

The list was constructed as a helical graph wrapped around a cylinder--elements with similar properties occupied positions on the same vertical line of cylinder (the list also included some ions and compounds). Using geological terms and published without the diagram, de Chancourtois ideas were completely ignored until the work of Mendeleev.

First Periodic Table

Parafuso Telúrico de Chancourtois

English chemist John Newlands (1837-1898), having arranged the 62 known elements in order of increasing atomic weights, noted that after interval of eight elements similar Physical /chemical properties reappeared.

Newlands was the first to formulate the concept of periodicity in the properties of the chemical elements.

Law of Octaves 1863

In 1863 he wrote a paper proposing the Law of Octaves:

Elements exhibit similar behavior to the eighth element following it in the table.

Lítio, potássio e sódio;

pela primeira vez,

juntos no modelo das

oitavas de Newlands

In 1869, Russian chemist Dimitri Mendeleev (1834-1907) proposed arranging elements by atomic weights and properties.

Mendeleev's periodic table of 1869 contained 17 columns with two partial periods of seven elements each (Li-F & Na-Cl) followed by two nearly complete periods (K-Br & Rb-I).

In 1871 Mendeleev revised the 17-group table with eight columns (the eighth group consisted of transition elements). This table exhibited similarities not only in small units such as the triads, but showed similarities in an entire network of vertical, horizontal, and diagonal relationships.

The table contained gaps but Mendeleev predicted the discovery of new elements. In 1906, Mendeleev came within one vote of receiving the Nobel Prize in chemistry.

Mendeleev's Periodic Table

Em 1869, enquanto escrevia seu livro de química inorgânica, organizou os elementos na forma da tabela periódica atual. Mendeleev criou uma carta para cada um dos 63 elementosconhecidos.

Cada carta continha o símbolo do elemento, a massa atômica e suas propriedades químicas e físicas.

Colocando as cartas em uma mesa, organizou-as em ordem crescente de suas massas atômicas, agrupando-as em elementos de propriedades semelhantes. Formou-se então a tabela periódica.

Julius Lothar Meyer (1830 - 1895).

Em 1869, Meyer e Mendeleyev, trabalhando independentemente, lançaram classificações periódicas semelhantes. Mas o brilhantismo das previsões de Mendeleyev ofuscou por completo o resultado das pesquisas de Lothar Meyer.

Em 1882, porém, os dois cientistas receberam a Medalha Davy, a mais alta honraria da Associação Britânica para o Progresso da Ciência.

Vale lembrar também que, em 1887, outra injustiça foi reparada. A mesma medalha foi oferecida a Newlands, o cientista que fora ridicularizado por sua classificação baseada nas oitavas musicais.

O cientista russo deixou alguns espaços vagos na sua tabela, justificando que esses locais eram reservados para o eventual ordenamento de elementos, na época, ainda desconhecidos, denominando-os de:

Eka-boro (abaixo do boro);Eka-aluminio (abaixo do aluminio);Eka-silício (abaixo do silício).

Demonstrando grande sagacidade científica, Mendeleyev definiu as propriedades desses elementos ainda desconhecidos.

A consagração de Mendeleyev

Suas previsões se mostraram corretas:

em 1874, o Eka-alumínio foi descoberto por L. Boisbaudran, recebendo o nome de Gálio;

cinco anos depois, Lars F. Nilson descobriu o Eka-boro, cuja denominação passou a ser de Escândio;

finalmente, em 1886, Clemens Alexander Winkler descobriu o Eka-silício, elemento hoje denominado de Germânio.

Para melhor compreensão, observe:

Previsões

A tabela abaixo mostra as propriedades do germânio e as propriedades previstas por Mendeleev para esse elemento, que na época era desconhecido e o qual Mendeleev nomeou de eka-silício.

4,74,74,74,7Densidade Densidade ÓÓxidoxido

Cinza claroCinza claroCinzentoCinzentoCorCor

5.475.475,505,50Densidade(Densidade(g/cg/cmm33))

72,672,67272Massa AtômicaMassa Atômica

GermânioGermânioEkaEka--SilSilííciocioPropriedadesPropriedades

A tabela abaixo mostra as propriedades do germânio e as propriedades previstas por Mendeleev para esse elemento, que na época era desconhecido e o qual Mendeleev nomeou de eka-alumínio.

GaGa22OO33((EAlEAl))22OO33ÓÓxidoxido

30,15 30,15 00CCBaixoBaixoPtoPto. de Fusão. de Fusão

5.945.945,95,9Densidade(Densidade(g/cg/cmm33))

69,769,76868Massa AtômicaMassa Atômica

GGááliolioEkaEka--AlumAlumíínionioPropriedadesPropriedades

In 1895 Rayleigh reported the discovery of a new gaseous element named argon. This element was chemically inert and did not fit any of the known periodic groups.

Ramsey followed by discovering the remainder of the inert gases and positioning them in the periodic table.

So by 1900, the periodic table was taking shape with elements were arranged by atomic weight. For example, 16g oxygen reacts with 40g calcium, 88g strontium, or 137g barium.

Rayleigh (physics) and Ramsey (chemistry) were awarded Nobel prizes in 1904. The first inert gas compound was made in 1962 (xenon tetrafluoride) and numerous compounds have followed

Lord Rayleigh (1842-1919)

William Ramsey (1852-1916)

When Moseley arranged the elements according to increasing atomic numbers and not atomic masses, some of the inconsistencies associated with Mendeleev's table were eliminated. The modern periodic table is based on Moseley's Periodic Law (atomic numbers).

At age 28, Moseley was killed in action during World War I and as a direct result Britain adopted the policy of exempting scientists from fighting in wars. Shown below is a periodic table from 1930:

Moseley's Periodic Law

Soon after Rutherford's landmark experiment of discovering the proton in 1911, Henry Moseley (1887-1915) subjected known elements to x-rays. He was able to derive the relationship between x-ray frequency and number of protons.

1872 - A tabela periódica de Mendeleyev.Os espaços marcados com traços representam elementos que Mendeleyev deduziuexistirem mas que ainda não haviam sido descobertos àquela época. Os símbolos no topo de cada coluna são as fórmulas moleculares escritas no estilo do século XIX.

The last major change to the periodic table resulted from Glenn Seaborg's work in the middle of the 20th century. Starting with plutonium in 1940, Seaborg discovered transuranium elements 94 to 102 and reconfigured the periodic table by placing the lanthanide/actinide series at the bottom of the table. In 1951 Seaborg was awarded the Nobel Prize in chemistry and element 106 was later named seaborgium (Sg) in his honor.

Modern Periodic Table

Dr. Timmothy Stowe's physicists periodic table.

The periodic spiral of Professor Theodor Benfey

A triangular long form periodic table by Emil Zmaczynski.

Superatoms

Superatoms are clusters of atoms which seem to exhibit some of the properties of elemental atoms.

Sodium atoms when left to condense in clusters from vapournaturally form into clusters of 8, 20, 40, 58 or 92 atoms (the magic numbers).

The suggestion is that free electrons in the cluster form atomic like structure

The atomic properties of this structure should mimic the atomic properties of atoms with filled s and p orbitals, i.e. the noble gases.

Jellium is the theory of interacting electrons in which a uniform background of positive charge exists. In this theory at zero temperature the system properties are dependent only on the density of electrons.

This allows for the simplistic calculation of the electron-electron coupling energy being a ratio between the free-electron kinetic energy and the Coulomb potential energy.

The jellium theory is used in nuclear physics. It has been used to try to explain the properties of superatoms.

Superatoms

A research team has discovered clusters of aluminum atoms that have chemical properties similar to single atoms of metallic and nonmetallic elements when they react with iodine.

The discovery opens the door to using 'superatom chemistry' based on a new periodic table of cluster elements to create unique compounds with distinctive properties never seen before.

Shiv N. Khanna, professor of physics at Virginia Commonwealth University and A. Welford Castleman Jr., the Evan Pugh Professor of Chemistry and Physics and the Eberly Family Distinguished Chair in Science at Penn State University

Clusters of Aluminum AtomsFound to Have Properties of Other Elements

14 January 2005 issue of the journal Science

Certain aluminium clusters have superatomproperties.

These aluminium clusters are generated as anions (Aln- with n = 1,2,3...) in a helium gas and reacted with a gas containing molecular iodine.

When analyzed by mass spectroscopy one main reaction product turns out to be Al13I-

These clusters of 13 Al atoms with an extra electron added does also appear not to react with oxygen when it is introduced in the same gas stream.

Assuming each atom liberates its 3 valence electrons, this meansthat there are 40 electrons present, which is one of the magic numbers noted above for sodium, and implies that these numbers are a reflection of the noble gases.

Calculations show that the additional electron is located in thealuminium cluster at the location directly opposite from the iodine atom. The cluster must therefore have a higher electron affinity for the electron than iodine and therefore the aluminium cluster is called a superhalogen.

The cluster component in Al13I- ion is similar to an iodine ion or better still a bromine atom. The related Al13I2- cluster is expected to behave chemically like the triiodide ion

This is only known to occur when there are at least 3 iodine atoms attached to an Al14- cluster, Al14I3-.

The anionic cluster has a total of 43 itinerant electrons, but thethree Iodine atoms each remove one of the itinerant electronsto leave 40 electrons in the jellium shell.

Similarly it has been noted that Al14 clusters with 42 electrons (2 more than the magic numbers) appear to exhibit the properties ofan alkali metal which typically adopt +2 valence states.

Science 2 April 2004: Vol. 304. no. 5667, pp. 84 - 87

Formation of Al13I-: Evidence for the Superhalogen Character of Al13Denis E. Bergeron,1 A. Welford Castleman, Jr.,1* Tsuguo Morisato,2 Shiv N. Khanna2

Al13– is a cluster known for the pronounced stability that arises from coincident closures of its geometric and electronic shells. We present experimental evidence for a very stable cluster corresponding toAl13I–.

Ab initio calculations show that the cluster features a structurally unperturbed Al13– core and a region of high charge density on the aluminum vertex opposite from the iodine atom. This ionically bound magic cluster can be understood by considering that Al13 has an electronic structure reminiscent of a halogen atom. Comparisons to polyhalides provide a sound explanation for our chemical observations.

Two classes of gas-phase aluminum-iodine clusters have been identified whose stability and reactivity can be understood in terms of the spherical shell jellium model. Experimental reactivity studies show that the Al13I –x clusters exhibit pronounced stability for even numbers of I atoms. Theoretical investigations reveal that the enhanced stability is associated with complementary pairs of I atoms occupying the on-top sites on the opposing Al atoms of the Al13– core. We also report the existence of another series, Al14I –x, that exhibits stability for odd numbers of I atoms. This series can be described as consisting of an Al14I –3 core upon which the I atoms occupy on-top locations around the Al atoms. The potential synthetic utility of superatomchemistry built upon these motifs is addressed.

Al Cluster Superatoms as Halogens in Polyhalidesand as Alkaline Earths in Iodide Salts

D. E. Bergeron, P. J. Roach,1 A. W. Castleman, Jr., N. O. Jones, S. N. Khanna

Pensar é o esporte mais radical que existe: pratique-o.

Prof. Dr. Arnaldo Dal Pino JúniorDep. de Física do ITA