Answer:
Energy levels
Step-by-step explanation:
Elements in one row of the periodic table have the same energy levels. A row on the periodic table is the horizontal arrangement of elements. These rows are called periods.
There are 7 periods on the periodic table.
- Each elements on a period begins with an atom having one valence electrons and then ending with completely filled orbitals.
- Elements in the same period are known to have the same electronic shells which is the energy level.
- The principal quantum number of their electrons is the same.