The main purpose of the study was to examine college students' individual mental models of the electric field through the description of how these mental models evolved and modified by instruction and group negotiation. Using a hybrid methodology of case study and grounded theory, this study examined one case participant in a cohort of 18 students by video-taped interviews, focus group discussions, and in-depth analysis of concept maps, drawings, and other student-generated outputs. Transcribed data from individual interview and focus group discussion were analyzed using the inductive procedure of grounded theory. Findings of the study revealed that the student represented and understood electric field using a one-size-fits all “attraction-and-repulsion core mental model”. For case participant, the electric field exhibited attraction and repulsion characteristics as represented by negative and positive charges. This core mental model was evident prior to instruction which was modified towards an increased level of sophistication after instruction and group negotiation. The study further revealed that (a) prior knowledge, (b) class instruction, and (c) group negotiation influenced the development and modification of college students' mental models in the electric field. Instruction and group negotiation play a vital role the development of college students' mental models of the electric field. Implications for teaching electromagnetics were advanced in the study.