Chapter 3 of CBSE Class 11 Chemistry, titled "Classification of Elements and Periodicity in Properties," explores the historical development and significance of the periodic table. The chapter begins with early efforts to categorize elements, leading to Mendeleev's groundbreaking periodic table, which arranged elements by atomic mass. It highlights the modern periodic table, organized by atomic number, and introduces key concepts such as periods, groups, and periodic trends in properties like ionization energy, electronegativity, and atomic radius. This understanding is vital for predicting the behavior of elements in chemical reactions and emphasizes the systematic nature of chemistry.