Question

both helium and beryllium have two electrons in the valence shells.helium is a noble gas where as beryllium is a metal,justify.

Answer 1

helium is a noble gas bcoz it remains unreactive whereas beryllium needs six electrons to complete its valence shell which is difficult from energy point of view so it loses its 2 electrons therefore it is a metal

Answer 2

Helium has 2 electrons in the first shell which can accomodate a maximum of 2 electrons. As the shell is completely filled, Helium is stable.
Beryllium has 2 electrons in the second shell which can accomodate a maximum of 8 electrons. As the shell is not completely filled, Beryllium is not stable.
Beryllium can lose two electrons to get a stable noble gas configuration. Thus it has an electron donating nature. Hence it behaves as a metal.

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