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Justify the position of hydrogen in the periodic table on the basis of its electronic configuration. |
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Answer» Solution :Hydrogen is the first element in the periodic table. However, its placement in the periodic table has been a subject of DISCUSSION in the past. Hydrogen has electronic configuration `1s^1` on one hand, its electron configuration is similar to the outer electronic configuration II `(ns^1)` of alkali metals, which belong to the first group of the periodic table. On the other hand, like halogens, it is short by, one electron to the corresponding NOBLE gas configuration. Hydrogen, therefore has resemblance to alkali metals, which lose one electron to form unipositive ions. Like alkali metals hydrogen forms oxides, halides and sulphides. However, unlike alkali metals, it has a very HIGH IONIZATION enthalpy and does not possess metallic characteristics under normal conditions. `Delta_i H` of Li is 520 kJ `"mol"^(-1)`,F is 1680 kJ `"mol"^(-1)` and that of H is 1312 kJ `"mol"^(-1)` Like halogens, hydrogen forms a diatomic molecule, combines with elements to form hydrides and a large number of COVALENT compounds. However, in terms of reactivity, it is very low as compared to halogens. Inspite of the fact that hydrogen, to a certain extent resembles both with alkali metals and Halogens, it differs from them as well. Loss of the electron from Hydrogen atom results in nucleus `(H^+)` of ~ `1.5xx10^(-3)` pm size. This is extremely small as compared to normal atomic and ionic sizes of 50 to 200 pm. As a consequence, `H^+` does not exist freely and is always associated with other atoms or molecules. Thus, it is unique in behaviour and is, therefore, best placed separately in the periodic table |
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