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Electronegativities Periodic Table of the Elements

Electronegativities Periodic Table of the Elements Home > Fundamental Physical Constants - Chemical - Physical - Thermochemical Data > Periodic Table with Electronegativities Periodic Table with Electronegativities   Electronegativity is defined as the ability of an atom in a molecule to attract electrons to itself. The electronegativity of an atom in a molecule is related to the atom's ionization energy and electron affinity , which are properties of isolated atoms. An atom with a high ionization energy and with a very negative electron affinity both resists having its electrons attracted away and attracts electrons from other atoms. It is highly electronegative. Linus Pauling developed the first and most widely used electronegativity scale which is based on thermochemical data (Table 1). There is generally an increase in electronegativity from left to right across a row of the periodic table. Electonegativity decr...
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Useful Conversion Factors between Units of Fundamental Physical Constants

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The SN2 reaction: Substitution Nucleophilic Bimolecular

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Several distinct mechanisms are possible for nucleophilic substitution reactions at saturated C atoms, depending on the substrate, nucleophile, leaving group and the reaction conditions. By far the most common are the S N 1 and S N 2 mechanisms. Simple alkyl groups, methyl and primary alkyl groups always react by the S N 2 mechanism and never by S N 1 . Why methyl and primary alkyl groups react by the S N 2 mechanism? What are the steps in an S N 2 mechanism? Partly because the corresponding cations are unstable and partly because it is easy for the nucleophile to attack the C atom since it is surrounded by H atoms – and not by bulky alkyl groups. Experimental results show the following in S N 2 reactions: In this mechanism (Fig. 1)  there is backside attack 1 . The nucleophile attacks the carbon atom on the opposite side from the leaving group – 180 away from the leaving group – and the carbon atom turns inside out as the reaction proceeds The reaction is a one-step proc...
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