<![CDATA[Purpose – This study aimed to diagnose students’ conceptual understanding and misconceptions in molecular geometry using three visuospatial indicators: molecular symmetry planes, mental rotation, and interpretation of 3D-to-2D representations.Methodology – A descriptive quantitative design was employed with 54 eleventh-grade students. Data were collected using a six-item two-tier diagnostic test, with two items representing each visual-spatial indicator. The instrument was reviewed by six experts using a five-point Likert scale and analyzed using Aiken’s V. Internal consistency was examined using dichotomously scored Tier 1 and Tier 2 responses. In contrast, the combination of the two tiers was used for diagnostic classification. Responses were classified into Conceptual Understanding, Misconception, and No Conceptual Understanding.Findings – The instrument obtained an overall Aiken’s V of 0.89, indicating adequate content validity across content relevance, two-tier construction, language and readability, and visual representation. The internal consistency coefficient was low (α = 0.41). Diagnostic analysis showed that Conceptual Understanding ranged from 7.41% to 31.48%, with the highest proportion in 3D-to-2D interpretation and the lowest in mental rotation. Misconceptions were highest in mental rotation (50.93%), followed by molecular symmetry planes (44.44%) and interpretation of 3D-to-2D representations (38.89%). Item-level analysis revealed difficulties in identifying reflection planes from molecular orientation, maintaining three-dimensional relationships during mental rotation, distinguishing mental rotation from reflection, integrating wedge–dash notation with tetrahedral structure, and distinguishing changes in visual representation from changes in molecular geometry.Contribution – This study contributes a visual-spatial perspective to two-tier diagnostic assessment by linking students’ misconception patterns to specific visual-spatial indicators, providing targeted information to understand and address conceptual difficulties in molecular geometry.]]>
