Periodic Classification of elements gives a brief idea about how elements are classified based on the similarities in the properties shared by different elements. It briefly discusses how Dobereiner classified various elements into triads and how Newland proposed the Law of Octaves. The chapter briefly discusses the arrangement of elements in increasing order of their atomic numbers and chemical properties as suggested by Mendeleev.
Elements in the Modern Periodic Table are arranged in 18 vertical columns called groups and seven horizontal rows called periods. Elements thus arranged show periodicity of properties including atomic size, valency or combining capacity and metallic and non-metallic character. The valency of an element is determined by the number of valence electrons present in the outermost shell of its atom. The term atomic size refers to the radius of an atom.