Multiple Choice
In the periodic table, what is a horizontal row called?
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4. Atoms and Elements
Periodic Table: Classifications
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How many periods (horizontal rows) are on the modern periodic table?
A
18
B
8
C
7
D
118
Verified step by step guidance1
Understand that the periodic table is organized into horizontal rows called periods, which represent elements with the same number of electron shells.
Recall that the modern periodic table consists of elements arranged in increasing atomic number, and these elements are grouped into 7 periods based on their electron configuration.
Recognize that each period corresponds to the filling of a principal energy level (shell) in the atom.
Note that while there are 18 groups (vertical columns), the number of periods (horizontal rows) is fixed at 7 in the modern periodic table.
Therefore, the number of periods on the modern periodic table is 7.
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