The correct order of thermal stability of hydroxides is :

Question

Reaction of $BeCl_2$ with $LiAlH_4$gives :

$AlCl_3$
$BeH_2$
$LiH$
$LiCl$
$BeAlH_4$

Choose the correct answer from the options given below :

Answer 1

The thermal stability of metal hydroxides generally increases down the group in the alkaline earth metals family (Group 2 of the periodic table). The alkaline earth metal hydroxides in this question are magnesium hydroxide $Mg(OH)_2$, calcium hydroxide $Ca(OH)_2$, strontium hydroxide $Sr(OH)_2$, and barium hydroxide $Ba(OH)_2$.

Let's examine why the order of thermal stability is as follows:

The thermal stability of hydroxides depends on the lattice energy and the polarization of the anion by the cation. As you go down the group, the lattice energy becomes less significant due to the increase in cation size.
The larger the metal cation, the lower its polarizing power, which results in less distortion of the hydroxide ion.
Barium has the largest ionic size among Ba, Sr, Ca, and Mg, thus barium hydroxide will have the least polarization and, consequently, the highest thermal stability.
Conversely, magnesium being the smallest cation in the list, will polarize the hydroxide ion the most, making $Mg(OH)_2$ the least thermally stable.

Therefore, the thermal stability of these hydroxides increases as follows:

$Mg(OH)_2 < Ca(OH)_2 < Sr(OH)_2 < Ba(OH)_2$

This means option three is the correct answer. The correct order of thermal stability is explained through the concepts of polarizing power and the trend in the group of alkaline earth metals.

Answer 2

The thermal stability of metal hydroxides generally increases down the group in the alkaline earth metals family (Group 2 of the periodic table). The alkaline earth metal hydroxides in this question are magnesium hydroxide $Mg(OH)_2$, calcium hydroxide $Ca(OH)_2$, strontium hydroxide $Sr(OH)_2$, and barium hydroxide $Ba(OH)_2$.

Let's examine why the order of thermal stability is as follows:

The thermal stability of hydroxides depends on the lattice energy and the polarization of the anion by the cation. As you go down the group, the lattice energy becomes less significant due to the increase in cation size.
The larger the metal cation, the lower its polarizing power, which results in less distortion of the hydroxide ion.
Barium has the largest ionic size among Ba, Sr, Ca, and Mg, thus barium hydroxide will have the least polarization and, consequently, the highest thermal stability.
Conversely, magnesium being the smallest cation in the list, will polarize the hydroxide ion the most, making $Mg(OH)_2$ the least thermally stable.

Therefore, the thermal stability of these hydroxides increases as follows:

$Mg(OH)_2 < Ca(OH)_2 < Sr(OH)_2 < Ba(OH)_2$

This means option three is the correct answer. The correct order of thermal stability is explained through the concepts of polarizing power and the trend in the group of alkaline earth metals.

The correct order of thermal stability of hydroxides is :

The Correct Option is C

Solution and Explanation

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