There are no strict rules about the number of chapters in a book or a specific word count per chapter. The structure of a book, including the number and length of chapters, is largely a stylistic choice and depends on the author's vision for the work.
However, certain genres and types of books may have common conventions. For example, young adult novels often have shorter chapters, while epic fantasy novels might have longer ones. Additionally, some authors prefer to maintain consistency in chapter length for pacing, while others vary chapter lengths to create a dynamic rhythm in their storytelling.
Ultimately, the key is to serve the needs of the story and engage the reader. Chapters should be organized in a way that enhances the flow of the narrative, keeps the reader's interest, and aligns with the author's artistic intentions. If you're writing a book, consider experimenting with different chapter structures to find what works best for your story and style.