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I have an old periodic table and I marked five metals from groups 1A and 2A with dots to indicate something about them. Only all this time later I can't figure out what exactly it was. I've been trying to figure it out for ages.

The elements are: Li, Na, K, Ca, Ba.

Doesn't anyone know any properties that just those elements, or maybe even just primarily those five, share that I could have been marking them for?

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    $\begingroup$ Their salts burn nice and colourful... red, yellow, purple, red, green (but there are many more that do that). See at wikipedia $\endgroup$ – Martin - マーチン Mar 4 '15 at 7:08
  • $\begingroup$ Maybe your assumption was the exam questions are about these five? Or it could be these elements' cations are commonly seen in ionic compounds? There are countless possibilities, that would render answering (better put it as guessing) this almost impossible. $\endgroup$ – M.A.R. Mar 4 '15 at 12:44
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They are all member of the s block in the periodic table. It means they all have valence electron in the s orbital.

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    $\begingroup$ other elements are also s-block and are not marked so I suspect that this is not the reason $\endgroup$ – bon Mar 4 '15 at 13:02

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