why does the d block start in the fourth row of the periodic table; how does the second row of the periodic table reflect the subshells of the second shell; the _____ on the outer level of an atom determines how an atom behaves.; why does the f-block not appear until the 6th row; why does the d block start at 3; second row elements in the periodic table; where are the transition elements located on the periodic table?; each electron energy level is represented by a different in the periodic table.