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Q. What other locations for elements are in question?

A. Hydrogen placement is problematic. Noted chemists and philosophers of science are divided as to whether the H data should be placed in a box over Li, F, C, or no one group. The criteria vary, from atomic number triads, to electronic configurations, to ionization energy, both for H and He, and likely for others as well.
        Details of answer;
      Because hydrogen forms compounds with oxidation numbers of both +1 and -1, many periodic tables include this element in both Group 1 (with Li, Na, K, Rb, Cs, and Fr) and Group 17 (with F, Cl, Br, I, and At). there are many reasons for including hydrogen among the elements in Group 1. It forms compounds (such as HCl and HNO3) that are analogs of alkali metal compounds (such as NaCl and KNO3). Under conditions of very high pressure, it has the properties of a metal. (It has been argued, for example, that any hydrogen present at the center of the planet Jupiter is likely to be a metallic solid.) Finally, hydrogen combines with a handful of metals, such as scandium, titanium, chromium, nickel, or palladium, to form materials that behave as if they were alloys of two metals.
      There are equally valid arguments for placing hydrogen in Group 17. It forms compounds (such as NaH and CaH2) that are analogs of halogen compounds (such as NaF and CaCl2). It also combines with other nonmetals to form covalent compounds (such as H2O, CH4, and NH3), the way a nonmetal should. Finally, the element is a gas at room temperature and atmospheric pressure, like other nonmetals (such as O2 and N2).
      Some people argue that hydrogen must be in the alkali metal column, and anything else is wrong, some people argue that hydrogen must be in the halogen column, and anything else is wrong, and some people put hydrogen somewhere in the middle.
      A 3-D periodic table can constitute a real alternative to flattened tables by permitting placement of elements in multiple conjunctions. For instance, the “Hydrogen Crown” of the Alexander Arrangement forms the first period, starting the table by looping down from above (star systems are mostly hydrogen) over the Noble Gases, the Non-Metals, and then attaches (beside the element in the following group,) to He of period two just above the Halogens. ).


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Detailed answer to “What other locations for elements are in question?”
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