The IBDP Chemistry 2025 Online Textbook has completed its first milestone, "Structure 1. Models of the particulate nature of matter," providing a solid foundation for subsequent topics in the specification. The online textbook aims to be an all-encompassing and interactive resource that facilitates learning and teaching in the IBDP Chemistry community. It covers key learning outcomes, practical work, quality questions for testing understanding, and in-class teaching materials. The creator invites collaboration to ensure the textbook's relevance and efficacy, and encourages everyone to explore the completed section and contribute to its development.