Textbook in PDF format This book offers an in-depth exploration of one of the fundamental particles that has shaped our understanding of the physical world and revolutionized technology, combining historical narrative with rigorous scientific analysis to provide a comprehensive account of the electron. Starting from the early atomic models of Democritus and Dalton, the book traces the journey through key experiments such as J.J. Thomson's discovery of the electron, Rutherford's model, and Bohr's contributions. It discusses how these foundational experiments and theories have paved the way for modern quantum mechanics