Foundational Chemistry Learning Gaps in Atomic Structure and the Periodic Table: Development and Application of a Diagnostic Mastery Assessment

Abstract

This study aimed to develop a valid and reliable assessment instrument and to determine the mastery levels of Grade 11 learners in Atomic Structure and the Periodic Table of Elements, which are foundational domains in senior high school chemistry. Utilizing a descriptive research design, the study involved 120 Grade 11 students from Betinan National High School as the primary respondents, while 150 senior high school students from Fatima National High School participated in the pilot testing of the researcher-developed instrument. The finalized 35-item multiple-choice mastery test underwent rigorous expert validation, item analysis, and reliability testing, yielding a high internal consistency coefficient (Cronbach’s α = 0.829). Learners’ performance data were analyzed using descriptive statistical techniques, including frequency counts and percentage distributions, and mastery levels were classified as Not Mastered, Least Mastered, Nearly Mastered, or Mastered. The results revealed that learners demonstrated an overall Least Mastered level of understanding, with a mean mastery score of 47%. Both Atomic Structure (49%) and the Periodic Table of Elements (45%) were classified within the same mastery category, with the majority of assessment items exhibiting high error rates. These findings indicate persistent conceptual difficulties in key areas such as subatomic particles, atomic number and mass number, electron configuration, and periodic trends. Collectively, the results highlight substantial gaps in learners’ conceptual understanding and underscore the necessity for instructional strategies that emphasize diagnostic assessment, multiple representations, and conceptually driven instruction to address misconceptions and strengthen foundational chemistry knowledge.