chemistry 12th class cbse notes

Group 18 elements: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn) having the electronic configuration ns2 np6, are named as noble gases. All these are gases and chemically unreactive.

General properties of noble gases

Atomic radii of noble gases:

Atomic radii of noble gases increase down the group due to the addition of a new shell at each step.

Ionisation enthalpy of noble gases:

They have very high ionization enthalpy because of completely filled orbitals. Ionisation enthalpy decreases down the group because of increase in size.

Electron gain enthalpy of noble gases:

Because of stable electronic configuration, noble gases have no tendency to accept the electron and therefore, have large positive values of electron gain enthalpy.

Melting and boiling point of noble gases:

Due to the weak dispersion forces, they have low melting and boiling point.

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