Question

What does the period number indicates?​

Answer 1

Answer:

As an atom's atomic number increases, its shells must accommodate an increasing number of electrons. The outermost shell is called the valence shell; the period number refers to this shell.

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Answer 2

Answer:

As an atom's atomic number increases, its shells must accommodate an increasing number of electrons. The outermost shell is called the valence shell; the period number refers to this shell.