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? a) the reactivity of the elements changed drastically. b) the state of the elements went from solid to liquid. c) the boiling point of the elements decreased dramatically. d) the size of the elements jumped from very large to very small.