Chapter 16, Problem 21R

To determine

To Fill: In the blank.

Answer to Problem 21R

Period

Explanation of Solution

Introduction:

The period is the horizontal arrangement of the element in the periodic table.

The period is the horizontal arrangement of the elements according to their increase in the atomic number. As one moves from the left to the right in the periodic table, number of the electrons in the valence shell increases. In the periodic table, there are seven periods. Elements in the same period do not to have similar chemical properties.

Conclusion:

The correct word is ‘Period’.