The thesis presents a survey of understanding of physical forms of substance and of water circulation in nature among the pupils of the seventh grade of primary school. The theoretical part presents the concepts of triple nature of chemical concepts; Johnstone's triangle with three levels of chemical concepts; interdependence of three levels of science concepts model; model of teaching and learning chemistry, and the results and key findings from various studies in the field of false understanding of physical forms of substance and chemical concepts related to them. Furthermore, the theoretical part of the thesis gives an overview of selected school textbooks and curricula of subjects Environmental Education, Natural Science and Technology and Natural Sciences from the first to the seventh grade of primary school. The empirical part presents the results of the tests analysis and the interpretation of results from the point of view of understanding of chemical concepts. The main purpose of the thesis was to determine the understanding of the concepts related to the physical forms of water, transitions between physical forms at the submicroscopic level, presentation of chemical concepts and understanding of the process of water circulation among pupils of the seventh grade of primary school. An adapted written test was prepared for the purpose of the survey, which covered the key chemical concepts related to the teaching content of physical forms of substance, transitions between physical forms of substance and water circulation in nature. 228 pupils of the seventh class of elementary schools from Ljubljana and its surroundings participated in the survey. The results of the survey indicate that the tested pupils of the seventh grade of primary schools do not have any difficulties in identifying the physical forms of substance at the submicroscopic level. The problems occur in the understanding of submicroscopic presentations of the condensation, evaporation and melting process. More than half of the tested pupils did not recognize the phase transition between liquid and gaseous form of substance based on the submicroscopic distribution of substance particles. The pupils also have difficulties understanding the chemical concepts related to the process of water circulation in nature, but they are familiar with the process.