92 somewhere in the middle of the continuum is the

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[92] Somewhere in the middle of the continuum is the ubiquitous common or standard form of periodic table. This is regarded as better expressing empirical trends in physical state, electrical and thermal conductivity, and oxidation numbers, and other properties easily inferred from traditional techniques of the chemical laboratory. [93] Janet left-step periodic table 1s H He 2s Li Be 2p 3s B C N O F Ne Na Mg 3p 4s Al Si P S Cl Ar K Ca 3d 4p 5s Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr 4d 5p 6s Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba 4f 5d 6p 7s La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra 5f 6d 7p 8s Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Uut Fl Uup Lv Uus Uuo Uue Ubn f-block d-block p-block s-block This form of periodic table is more congruent with the order in which electron shells are filled, as shown in the accompanying sequence in the left margin (read from top to bottom, left to right). The placement of helium (a noble gas) above beryllium (an alkaline earth metal) ordinarily attracts strong criticism from chemists. Open questions and controversies Elements with unknown chemical properties Although all elements up to ununoctium have been discovered, only elements up to hassium (element 108), along with copernicium (element 112), have known chemical properties. The other elements may behave differently from what would be predicted by extrapolation, due to relativistic effects; for example, flerovium has been predicted to possibly exhibit some noble-gas-like properties, even though it is currently placed in the carbon group. [94] More recent experiments have suggested, however, that flerovium behaves chemically like lead, as expected from its periodic table position. [95] Further periodic table extensions Main article: Extended periodic table It is unclear whether new elements will continue the pattern of the current periodic table as period 8, or require further adaptations or adjustments. Seaborg expected the eighth period, which includes a two-element s-block for elements 119 and 120, a new g-block for the next 18 elements, and 30 additional elements continuing the current f-, d-, and p-blocks. [96] More recently, physicists such as Pekka Pyykkö have theorized that these additional elements do not follow the Madelung rule, which predicts how electron shells are filled and thus affects the appearance of the present periodic table. [97] Element with the highest possible atomic number The number of possible elements is not known. A very early suggestion made by Elliot Adams in 1911, and based on the arrangement of
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6/2/13 11:44 AM Periodic table - Wikipedia, the free encyclopedia Page 12 of 17 http://en.wikipedia.org/wiki/Periodic_table elements in each horizontal periodic table row, was that elements of atomic weight greater than 256± (which would equate to between elements 99 and 100 in modern-day terms) did not exist.
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