Periodicity in Properties After studying this Unit, you will be able to • appreciate how the concept of grouping elements in accordance to their properties led to the development of Periodic Table. • understand the Periodic Law; • understand the significance of atomic number and electronic configuration as the basis for periodic classification; • n a m e t h e e l e m e n t s w i t h Z > according to IUPAC nomenclature; • classify elements into s , p , d , f blocks and learn their main characteristics; • recognise the periodic trends in physical and chemical properties of elements; • compare the reactivity of elements and correlate it with their occurrence in nature; • explain the relationship between ionization enthalpy and metallic character; • use scientific vocabulary appropriately to communicate ideas related to certain important p r o p e r t i e s o f a t o m s e . g . , atomic/ionic radii, ionization enthalpy, electron gain enthalpy, electronegativity, valence of elements.
In this Unit, we will study the historical development of the Periodic Table as it stands today and the Modern Periodic Law. We will also learn how the periodic classification follows as a logical consequence of the electronic configuration of atoms. Finally, we shall examine some of the periodic trends in the physical and chemical properties of the elements. .
WHY DO WE NEED TO CLASSIFY ELEMENTS ? We know by now that the elements are the basic units of all types of matter. In , only elements were known. By , the number of identified elements had more than doubled to .
At present elements are known. Of them, the recently discovered elements are man-made. Efforts to synthesise new elements are continuing. With such a large number of elements it is very difficult to study individually the chemistry of all these elements and their innumerable compounds individually.
To ease out this problem, scientists searched for a systematic way to organise their knowledge by classifying the elements. Not only that it