Question

11) The boiling points gas of noble gases are shown below Ne Kr -246°C -186°C -152°C Xe -107°C a. Rank the gases in order of increasing strength of intermolecular forces. b. Rank the gases in order of increasing atomic radius. c. Define and use the concept of Zef to explain the trends.

Answer 1

The boiling points of the noble gases increase as their atomic masses increase. Due to increase in van der waals force. Increase in size increase the van der waal's forces thus boiling point increases.

(a) order of intermolecular forces is Xe >Kr > Ar> Ne because stronger an intermolecular force, the higher the boiling point of the substance will be. This is because stronger intermolecular bonds require more energy to break. As this energy is supplied in the form of heat when boiling, substances with stronger bonds will have a higher boiling point.

(b) Increaseing order of atomic radius is Xe > Kr > Ar > Ne because down the group size increases. As van der Waals forces or weak London dispersion forces are present between the atoms of the noble gases in the liquid or the solid state.

The van der Waals force increases with the increase in the size of the atom, and therefore, in general, the boiling and melting points increase from He toRn.

(c) Zeff is defined as the effective nuclear charge that an electron experiences from the nucleus due to the shielding of inner electrons so lesser Zeff maximum is size.

And Zeff reaches a maximum at the noble gas configuration (Zeff = 8). With this electronic configuration, each electron feels the pull of 8 protons on it. Since Zeff reaches maximum thus there is no screening effect from the electrons in noble gases.

If you have any doubt then mention in the commant.