Why does H₂Se have a bigger Ka2 than H₂Te

Why does $\ce{H2Se}$ have a bigger $K\_\text{a2}$ than both $\ce{H2S}$ and $\ce{H2Te}$?




The following data are from the *Rubber Book* (CRC Handbook of Chemistry and Physics), 89th edition, 2009, p 8-40. 


\begin{array}{lll}
\mathrm{acid} & \mathrm{pK\_{a1}} & \mathrm{pK\_{a2}} \\
\hline
\ce{H2S} & 7.05 & 19\\ 
\ce{H2Se} & 3.89& 11\\
\ce{H2Te} & 2.6 & 11\\
\end{array}


Note that $\mathrm{pK\_{a1}}$ of $\ce{H2Te}$ was determined at 18 °C, all other data at 25 °C


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