JPII 11(4) (2022) 511-518 Jurnal Pendidikan IPA Indonesia http://journal.unnes.ac.id/index.php/jpii ENHANCEMENT OF INDONESIAN HIGH SCHOOL STUDENT CONCEPTUAL MASTERY ON VSEPR TOPIC USING VIRTUAL SIMULATION OF MOLECULE SHAPES: A CASE STUDY OF QUASI-EXPERIMENTAL EVIDENCE E. Stiawan* 1 , R. Basuki 2 , L. Liliasari 3 , I. Rohman 4 1,2 Military Chemistry Department, Faculty of Military Mathematics and Natural Sciences, Republic of Indonesia Defense University, Indonesia 3,4 Chemistry Education Department, Faculty of Mathematics and Natural Sciences Education, Universitas Pendidikan Indonesia, Indonesia DOI: 10.15294/jpii.v11i4.36385 Accepted: April 30 th 2022. Approved: December 29 th 2022. Published: December 30 th 2022 ABSTRACT The Valence Shell Electron Pair Repulsion (VSEPR) is an essential topic for high school student’s fundamental understanding of 3D shapes of chemical compounds. Due to the spatial aspect of the topic, the students were forced to imagine the geometry of the molecule by predicting the free or bonded electron pair repulsion. Suitable learning media to accommodate those features should be precisely selected to help students properly understand the geometry of the molecule based on the VSEPR topic. This study compared the significant difference in the application of two media of animation video and interactive simulation toward the control and experimental groups, respectively, to enhance conceptual mastery of the VSEPR topic. This study was a statistical quasi-exper- iment study with two classes of control (animation video) and experimental (interactive simulation) groups. The results of the significant difference test of the groups showed that the distribution of the experimental and control groups was not normal (significantly different) and normal (not significantly different), respectively. Analysis results using Mann-Whitney for the non-parametric free two samples comparative test with a 95% confidence level showed that the application of virtual simulation on the experimental group impacted more in improving the conceptual mastery of the VSEPR topic. Furthermore, there was an identified significant improvement in sub-concepts of the VSEPR topic in binding pair, molecular shape, and electron repulsion. These findings could support the teachers in designing lesson plans for students to master the VSEPR topic. © 2022 Science Education Study Program FMIPA UNNES Semarang Keywords: conceptual mastery; learning media; virtual simulation; VSEPR topic *Correspondence Address E-mail: elvastiawan@gmail.com INTRODUCTION The VSEPR topic, as one of the chemistry topics at the high school level, emphasizes basic understanding of molecular geometry of simple covalent compounds. This concept is considered fundamental for a further chemistry topic, especi- ally in organic chemistry and biochemistry. Many studies have reported that some students found difficulties in imagining three-dimensional struc- tural molecule shapes (Rahmawati et al., 2021). The topic regarding the geometry of molecules categorized as abstract is the main reason for stu- dents’ difficulties in properly visualizing molecu- le shapes (Kiernan et al., 2021). Instead of using the widely used physical VSEPR model, sometimes called a moly mod kit, some digital learning media can also help stu- dents visualize the geometry of molecule shapes, for example, animation video, and virtual simula- tion. As multimedia-based learning and molecule visualizations have transformed over the past de-