The helium atom contains two electrons on the external energy level, like the atoms of beryllium and magnesium. Why is helium placed in the Periodic Table of D.I. Mendeleev in the VIIIA group, and not in the IIA group?
Elements located in one group are characterized by the similarity of their properties. Helium is a non-metallic element, beryllium and magnesium are metallic.
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