Answer:Groups: The vertical column of the periodic table that signifies the number of valence electrons in an element. Periods: The horizontal rows in the periodic table that signify the number of electron shells in an element.
Explanation:
The table has seven rows and 18 columns. Each row represents one period; the period number of an element indicates how many of its energy levels house electrons.The columns of the table represent groups, or families, of elements.
