Why is LiH more stable to heat compared to NaH?

The lithium cation is harder than the sodium cation. The hydride ion is soft. Hence, I would assume that LiH would be more stable compared to NaH, owing to the better interaction that results between a less hard and soft species (NaH) over the interaction between two species of more extreme hardness (LiH).

  • 2
    $\begingroup$ Softness and hardness are not good indicators of thermal stability. $\endgroup$
    – Todd Minehardt
    Oct 2 '21 at 18:42
  • $\begingroup$ chemistry.stackexchange.com/questions/71598/… $\endgroup$
    – Mithoron
    Oct 2 '21 at 19:27
  • $\begingroup$ What could be some attributes that hardness and softness are precise indicators of? @ToddMinehardt $\endgroup$ Oct 3 '21 at 18:41
  • $\begingroup$ Resistance to abrasion and deformation (here). Google "Mohs scale" and go from there. $\endgroup$
    – Todd Minehardt
    Oct 3 '21 at 18:44
  • $\begingroup$ Wait. I was referring to hardness and softness in regard with the HSAB theory. $\endgroup$ Oct 3 '21 at 18:50

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