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NCERT Chemistry class 12- Group 16 Elements  NCERT Chemistry class 12 -  Group 16 elements are known as  the oxygen family or chalcogens.  They include elements oxygen (O), sulphur (S), selenium (Se), tellurium (Te), and the radioactive element polonium (Po). ATOMIC AND PHYSICAL PROPERTIES Atomic and Ionic Radii:  The atomic and ionic radius of the  group 16 elements  increases as one move from oxygen to polonium (top to bottom).As the number of shells increases on going down the group, atomic and ionic radii increase from top to bottom in the group. However, the size of oxygen atoms is exceptionally small. Ionization Enthalpy:  Ionisation enthalpy of the elements decrease down the group, as there is an increase in the size of the atoms down the group. However, the element of group 16 has lower ionization enthalpy values as compared to those of group 15 in the corresponding periods. This is due to the fact that group 15 element have extra stable half-filled p orbitals el