Which term describes a horizontal row of the periodic table in which elements have the same number of electron shells?

Which term describes a horizontal row of the periodic table in which elements have the same number of electron shells?

• A. Period
• B. Group
• C. Column
• D. Family

Answer: (A)

The term for a horizontal row describing elements that have the same number of electron shells is period. This row reflects atoms sharing the same principal energy level, or shell count, as you move across it. As you go from left to right within a period, you add protons and electrons to the same shell, so the number of shells stays the same while other properties change gradually. In contrast, vertical columns are groups (also called families), which describe elements with similar chemical behavior due to their valence electrons, not their shell count. So the horizontal arrangement matching the same number of electron shells is called a period.

The term for a horizontal row describing elements that have the same number of electron shells is period. This row reflects atoms sharing the same principal energy level, or shell count, as you move across it. As you go from left to right within a period, you add protons and electrons to the same shell, so the number of shells stays the same while other properties change gradually. In contrast, vertical columns are groups (also called families), which describe elements with similar chemical behavior due to their valence electrons, not their shell count. So the horizontal arrangement matching the same number of electron shells is called a period.