1. Atomic and ionic radii : In groups 16, 17, 18 the atomic and ionic radii increase down the group, due to increase in the number of quantum shells. Across a period atomic or ionic radii decrease due to increase in effective nuclear charge.
2. Ionisation enthalpy :
- The elements of groups 16, 17 and 18 have a high ionisation enthalpy
- In groups 16, 17, 18 the ionisation enthalpy decreases down the group, due to increase in atomic size.
3. Electronegativity : In groups 16, 17, 18 the electronegativity decreases down the group.
4. Electron gain enthalpy :
- In groups 16 and 17 the electron gain enthalpy becomes less negative down the group.
- Group 18 elements have large positive electron gain enthalpy.
