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  2. Conrotatory and disrotatory - Wikipedia

    en.wikipedia.org/wiki/Conrotatory_and_disrotatory

    In organic chemistry, an electrocyclic reaction can either be classified as conrotatory or disrotatory based on the rotation at each end of the molecule. In conrotatory mode, both atomic orbitals of the end groups turn in the same direction (such as both atomic orbitals rotating clockwise or counter-clockwise). In disrotatory mode, the atomic ...

  3. Periodic table - Wikipedia

    en.wikipedia.org/wiki/Periodic_table

    The periodic table and law are now a central and indispensable part of modern chemistry. The periodic table continues to evolve with the progress of science. In nature, only elements up to atomic number 94 exist; [ a ] to go further, it was necessary to synthesize new elements in the laboratory.

  4. Pauling's rules - Wikipedia

    en.wikipedia.org/wiki/Pauling's_rules

    The effect is largest for cations with high charge and low C.N. (especially when r+/r- approaches the lower limit of the polyhedral stability). Generally, smaller elements fulfill the rule better. [6] As one example, Pauling considered the three mineral forms of titanium dioxide, each with a coordination number of 6 for the Ti 4+ cations.

  5. Selection rule - Wikipedia

    en.wikipedia.org/wiki/Selection_rule

    The Laporte rule is a selection rule formally stated as follows: In a centrosymmetric environment, transitions between like atomic orbitals such as s-s, p-p, d-d, or f-f, transitions are forbidden. The Laporte rule (law) applies to electric dipole transitions, so the operator has u symmetry (meaning ungerade, odd).

  6. Diagonal relationship - Wikipedia

    en.wikipedia.org/wiki/Diagonal_relationship

    The organization of elements on the periodic table into horizontal rows and vertical columns makes certain relationships more apparent (periodic law). Moving rightward and descending the periodic table have opposite effects on atomic radii of isolated atoms. Moving rightward across the period decreases the atomic radii of atoms, while moving ...

  7. Chemical law - Wikipedia

    en.wikipedia.org/wiki/Chemical_law

    The third stoichiometric law is the law of reciprocal proportions, which provides the basis for establishing equivalent weights for each chemical element. Elemental equivalent weights can then be used to derive atomic weights for each element. More modern laws of chemistry define the relationship between energy and transformations.

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  9. Pauling's principle of electroneutrality - Wikipedia

    en.wikipedia.org/wiki/Pauling's_principle_of...

    There are two possible structures for hydrogen cyanide, HCN and CNH, differing only as to the position of the hydrogen atom. The structure with hydrogen attached to nitrogen, CNH, leads to formal charges of -1 on carbon and +1 on nitrogen, which would be partially compensated for by the electronegativity of nitrogen and Pauling calculated the net charges on H, N and C as -0.79, +0.75 and +0.04 ...