The 3rd period of the long form of the periodic table contains only 8 elements because: — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

In the 3rd period ($n=3$), electrons fill the 3s and 3p subshells. According to the Aufbau principle, the 4s subshell is lower in energy than 3d, so 3d filling is delayed to the 4th period. Thus, only 8 electrons ($2+6$) are accommodated.