March's Organic Chemistry (7th ed - page 337 under "Periodic Table Correlations" in chapter "Acids and Bases") states that:

$\ce{H3O+ > H3S+ > H3Se+}$ is the acidity order of these charged group 16 hydrides

I am trying to make out why this is true. I have seen the related questions but they are about the neutral hydrides and not charged ones.

My working was that the order of acidity should be the reverse order of the basicity of their conjugate bases. The conjugate bases are $\ce{H2O,H2S, H2Se}$. We know that basicity decreases down the group, as the lone pair becomes more dispersed over the large surface area (corroborated for group 15). Hence, according to me, order of basicity order is $\ce{H2O>H2S> H2Se}$. Hence, order of acidity should be $\ce{H3O+<H3S+<H3Se+}$. But, in March, the reverse order is given.

What is the reason for this order given by March? And what is wrong in my logic?

  • $\begingroup$ The order is correct. $\endgroup$
    – Mithoron
    Commented Feb 21, 2018 at 19:36
  • $\begingroup$ @Mithoron What's the reason behind that? $\endgroup$
    – Archer
    Commented Feb 22, 2018 at 5:37


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