Question

why first period in the periodic table have two elements.​

Answer 1

Answer:

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Explanation:

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.