Question

Fill in the blanks based on features of Mendeleev's periodic table:

The horizontal rows are called --------

Answer 1

Mendeleev periodic table:

• In Mendeleev periodic table elements were arranged based on increasing atomic mass. During Mendeleev, only 63 elements were known so after studying the properties of elements, he arranged them into vertical columns called groups and horizontal rows are called periods.
• During arrangement, there were seven periods and eight groups in Mendeleev's periodic table.

Hence, The horizontal rows are called periods.