I am asking this because after studying periodic properties and trends of elements I have come to an understanding that these two elements ($\ce{Be \& Mg}$) are many of the time exception to the general trend followed by most of the metals (especially s-block), for instance:

$•$ Except for $\ce{Be \& Mg}$ all s-block elements impart color to the flame.

$•$ With exception of $\ce{Be \& Mg}$ all s-block elements decompose water and readily evolve hydrogen gas.

$•$ Electron gain enthalpy is negative for all metals except $\ce{Be \& Mg}$.

From this I concluded that there is something special about the electronic configuration of these elements. Is my conclusion is true then why? And if not why do these cases occur?

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    $\begingroup$ Include also Li, being special among alkaline metals. There is also considered the diagonal similarity Li-Mg, Be-Al. $\endgroup$ – Poutnik Oct 19 at 13:36
  • $\begingroup$ en.wikipedia.org/wiki/Diagonal_relationship $\endgroup$ – Poutnik Oct 19 at 13:45
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    $\begingroup$ Meh, and hydrogen is normal, then? Or just so special that it's completely outside of your narrow comparison? FYI you could call top two elements in all groups of s & p block "special" - first one really special and second somewhat special. $\endgroup$ – Mithoron Oct 19 at 13:45
  • $\begingroup$ No you understood it quite wrong(maybe because I wasn't able to express myself) but I'm not talking about diagonal relationship nor I'm excluding other 'special' elements. What I wanted to know was why such instances arose. $\endgroup$ – The Last Airbender Oct 19 at 14:31
  • $\begingroup$ Because their size is too small & nuclear attractive force is too big. $\endgroup$ – abu sayed Oct 19 at 15:20

Tl, dr: Upon further review the differences between beryllium, magnesium and other metals is not so clear-cut.

There is less to the difference in flame colors than meets the eye. We do not have polar opposites of colored flames at one end and white flames at the other. Potassium does not introduce a strong color to the flame even though we often call the flame violet:


You need an optical aid (cobalt glass) to see anything at all:


As for the reaction with water, ask an organic chemist how inert magnesium is with respect to water. Water must be rigorously excluded to have any chance at forming a Grignard reagent. Most sources, including Wikipedia, now deem magnesium as reactive to water, albeit slowly.

Finally, it is true that beryllium and magnesium have positive enthalpies for electron gain, but plenty of metals, including all alkaline earth metals, do not favor actually gaining electrons under reasonable conditions. A filled valence subshell, such as $s^2$ in the alkaline earth metals or $d^{10}$ in zinc (listed here as having zero electron affinity), will do that.

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    $\begingroup$ Though I can't upvote it but your answer helps quite alot $\endgroup$ – The Last Airbender Oct 20 at 1:41

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