There are seven horizontal rows of the periodic table, called periods. The length of each period is determined by the number of electrons that are capable of occupying the sublevels that fill during that period.
Based on electron configurations, the periodic table can be divided into blocks denoting which sublevel is in the process of being filled, s, p, d, and f blocks.
The horizontal rows of the periodic table are called periods.
The length of a period depends on how many electrons are needed to occupy the sublevels that fill the period.
Blocks indicate which sublevel is being filled.