Returns the periodic table row of the element.

def row(self):
        """
        Returns the periodic table row of the element.
        """
        z = self.Z
        total = 0
        if 57 <= z <= 71:
            return 8
        elif 89 <= z <= 103:
            return 9

        for i in range(len(_pt_row_sizes)):
            total += _pt_row_sizes[i]
            if total >= z:
                return i + 1
        return 8