Question

What do all atoms in a period (horizontal rows) have in common?

Answer 1

Step-by-step explanation:

Elements in the same period are those that are in a single horizontal line from left to right. They do not share the same type of chemical reactivity as seen in groups. They only real thing that these elements share in common is the same principal quantum number, or main energy shell.

Answer 2

All of the elements in a period have the same number of atomic orbitals. For example, every element in the top row (the first period) has one orbital for its electrons. All of the elements in the second row (the second period) have two orbitals for their electrons.

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