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What Is the Difference Between an Element Group and Period?

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Question: What Is the Difference Between an Element Group and Period?
Groups and periods are two ways of categorizing elements on the periodic table. Here is how to tell them apart and how they related to periodic table trends.
Answer: Periods are horizontal rows (across) the periodic table, while groups are vertical columns (down) the table. Atomic number increases both as you move down a group or across a period.

Element Groups

Elements in a group share a common number of valence electrons. For example, all of the elements in the alkaline earth group have a valence of 2. Elements belonging to a group typically share several common properties.

Element Periods

Elements in a period share a highest unexcited electron energy level. There are more elements in some periods than others because the number of elements is determined by the number of electrons allowed in each energy sublevel.

Learn More

Groups and Periods
Overview of the Element Groups
Periodic Properties of the Elements

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