Why first period in the morden periodictable contain only two elements

1.	Why first period in the morden periodictable contain only two elements
Answer» There are only two ELEMENTS in the first period: hydrogen and helium. ... This is because in QUANTUM physics, this period fills up the 1s orbital. Period 1 elements follows the duet rule, they only need two electrons to complete their valence shell. These elements can only hold two electrons, both in the 1s orbital.Explanation:I hope it will help you have a nice DAY ahead

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