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why the stability of ionic hydrides decreases down the group because as i see ionic character increases down the group so licl

why the stability of ionic hydrides decreases down the group because as i see ionic character increases down the group so licl

Grade:12th pass

2 Answers

Aarti Gupta
askIITians Faculty 300 Points
8 years ago
Alkali metals(Li,Na,K etc) react with dry hydrogen at about 673K and form colourless crystalline hydrides.All the alkali metal hydrides are ionic solids with high melting points.These hydrides are strong reducing agents.
The stability of hydrides decrease from Li to Cs.It is because of the fact that M-H bond becomes weaker due to increase in the size of alkali metals down the group and the size of alkali metals increases as we move down the group as new shell is progressively added.Although,the nuclear charge also increases down the group but the effect of addition of new shells is more predominant due to increasing screening effect of inner filled shell on the valence s-electrons.Hence the atomic size increases in a group.
The order of reactivity of the alkali metals towards hydrogen decreases as we move down the group from Li to Cs which is due to the reason that the lattice energies of these hydrides decreases progressively as the size of the metal cation increases and thus the stability of these hydrides decreases from LiH to CsH.



ankit singh
askIITians Faculty 614 Points
3 years ago
fact,learn itThe order of reactivity of the alkali metals towards hydrogen decreases as we move down the group from Li to Cs which is due to the reason that the lattice energies of these hydrides decreases progressively as the size of the metal cation increases and thus the stability of these hydrides decreases from LiH to CsH.

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