Respuesta :

They all have the same number of electrons in their outer shell. This determines their valence level. So that's also what they have in common. Hope this helps. 

The thing that the elements in the same period have in common is the same number of atomic orbitals.

It should be noted that the elements that are in the same period have the same number of valence electrons. This implies that they have the same number of atomic orbitals.

For example, the elements that are in the top row which is the first period have one atomic orbital. The elements that are in a particular row have identical number of electron shells.

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