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Jaron, , 5.2 periodit trends in physical properties, Many physical properties of elements, ach as melting point, boiling point and density, a a periodicity. In this section we are going, A consider the periodic trends in physical, properties with reference to atomic radius,, ionic radius, ionization enthalpy, electron gain, enthalpy and electronegativity., a. Atomic radius : You have learnt in chapter, 4 that the quantum mechanical model of atom, describes the extranuclear part of atom as, thefelectron cloud, As a direct implication of, this, the atom has no definite boundary. The, atomic size ,or atomic radius, therefore, can, be estimated from the internuclear distance ., under different circumstances] In the case of, nonmetals (except noble gases), the atoms, of an element are bonded to each other by, covalent bonds. (Refer to Chapter 5). Bond, length of a single bond is taken as sum of radii, of the two single bonded atoms. This is called, covalent radius of the atom. For example, ‘ (i) Bond length of C-C bond in diamond is, 154 pm. Therefore, atomic radius of carbon