Abstract
This study empowers to investigate and compare the student’s alternative conceptions on the concept of periodicity which was reasoned from teaching the Modern and the Mendeleyev periodic systems (the MPS and the MEPS) and find out the impacts on students’ conceptions taught with two contents` knowledge and only one type of the periodic table. In this study, 96 secondary school students were involved including 39 Kazakh- Turkish high school students and 57 Gymnasium students. The Periodical Conceptual Question Paper (PSQP) was developed and composed of six major questions; true-false propositions; and one question was open ended. The reliability tests demonstrated satisfactory internal consistency (KR-20 = 0.71.) The study results showed that P <0.05 was statistically significant for the ratio of alternative concepts (AC1, AC2, AC6) of both the MPS and the MEPS contents and the students` achievements. Three alternative conceptions were found by the students, and it was proved that alternative conceptions of students were decreasing while students were taught with comparing alternative two contents in the teaching process. Finally, teaching with various content knowledge and periodic tables enables students to better understand the periodicity concept.