What do the groups (columns) and periods (rows) tell you about the elements on the periodic table?

Groups: The vertical column of the periodic table that signifies the number of valence electrons in an element.

Period: The horizontal rows in the periodic table that signify the number of electron shells in an element.

Explanation:

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.

- decrease the number of plants and animals living in the water.