The sixth period of the periodic table is the longest. It contains 32 elements.
Understanding Periods in the Periodic Table
The periodic table organizes elements into rows called periods and columns called groups. The number of elements in each period varies. This variation is due to the filling of electron shells and subshells as atomic number increases.
- Period 1: Contains only 2 elements (Hydrogen and Helium)
- Period 2 & 3: Contain 8 elements each.
- Period 4 & 5: Contain 18 elements each.
- Period 6: Contains 32 elements, including the lanthanides.
- Period 7: Incomplete, but also contains 32 elements including the actinides if they were all discovered.
Why the Sixth Period is the Longest
The sixth period (also known as the sixth row) includes not only the s and p block elements but also the d-block transition metals and the f-block lanthanides. The filling of the 4f subshells (lanthanides) in addition to the 6s, 5d, and 6p orbitals, accounts for its length. Because of the placement of the lanthanide and actinide series at the bottom of most depictions of the periodic table, people sometimes misunderstand that it is rows six and seven on the table itself which are the longest.
Summary
The sixth period of the periodic table is the longest, encompassing 32 elements due to the inclusion of lanthanides and the filling of various electron subshells.
