When Dimitri Mendelev first developed the periodic table, one of the most important features that he introduced was starting a new row at a certain point. What factor was most important to Mendelev in knowing when to end a row (period) and start a new one
When elements started to show drastically different properties he knew to end the period and start a new row.
Explanation:
Mendelev arranged elements according to their atomic mass and not atomic number. Mendeleev discovered that the physical and chemical properties of element vary periodically and that is how he arranged the elements in the periodic table. He left gaps for undiscovered elements and those elements that were indeed discovered later where found to have properties close to Mendelev’s prediction.
