Periods on the Periodic Table represent the and have the same number of .

A. rows; atomic orbitals or shells
B. Rows; electrons in the outer shell
C. Columns; electrons in the outer shell
D. Columns; atomic orbitals or shells
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A. rows; atomic orbitals or shells

When you look at the periodic table, each row is called a period (Get it? Like PERIODic table.). 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 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.

Vertical columns in the periodic table are groups of elements with similar properties

Explanation: