Chemistry is defined as the study of atoms, molecules, and subatomic particles, focusing on their interactions and reactions with their surroundings. It encompasses the composition of substances and the changes they undergo due to alterations in molecular structure, which are influenced by variations in the number, type, or arrangement of atoms. The discussion highlights the overlap between chemistry and physics, emphasizing the molecular nature of matter and change. A simplified definition presented is "the molecular nature of matter and change," while another perspective describes chemistry as an exploration of the collective interactive behavior of atom-groups in relation to electromagnetism.