Group 18 Elements

GROUP 18 ELEMENTS

Introduction: Group 18 consists of Helium,Neon,Argon,Krypton,Xenon,Radon and Ununoctium. 

The elements in group 18 have their valence shell orbits completely filled and therefore react with a few elements only under certain conditions therefore they are known as noble gas.All noble gasses are colourless,odorless and tasteless.

                                                                                                            

Occurrence: All the noble gasses except  Radon occur in the atmosphere.Radon is obtained as a decay product of  Radium.

Electronic configuration:  All noble gasses have general electronic configuration ns2 np6  except Helium which is 1s2 .

Ionization Enthalpy:  Due to stable electronic configuration these gasses exhibit very high ionization enthalpy. It decreases down the group with increase in atomic size.

Atomic Radii: atomic radii increases down the group with increase in atomic number.

Electron Gain Enthalpy: Since noble gasses have stable electronic configuration they have no tendency to accept the electron and therefore have large positive values of electron gain enthalpy.

Atomicity: All noble gasses are mono-atomic.

M.P & B.P: They have very low melting and boiling point because the only type of inter-atomic interaction in these elements is weak dispersion forces.

                                                                                                            

Compounds of noble gasses

Xenon-Fluorine compounds & Xenon - oxygen compounds

1. XeF2 :-  

Structure: 

According to VSEPR Theory XEF2 have linear structure and involves sp3d hybridization. 

Reactions:

A. reaction with water:

B. reaction with fluoride ion acceptors: 

                                                                                                            

XeF2+ PF5→[XeF]+[PF6]

XeF2+ PF5→[XeF]+[PF6]

XeF2+ PF5→[XeF]+[PF6]

XeF2+ PF5→[XeF]+[PF6]–

2.XeF4 : 

Structure:

according to VSEPR theory XeF4 have square planar structure sp3d2 hybridization.

Reactions:

A. Reaction with water :Hydrolyssis of XeF4  with water gives XeO3,, XeO3 is a colourless explossive solid and has pyramidal molecular structure.

B.Reaction with Fluoride ion acceptor:

                                                                                                            

3. XeF6: 

Structure:  

XeF6 has seven electron pairs and thus have distorted octahedral structureand have sp3d3 hybridization.

Reactions: 

A. Reaction with water :

B.Reaction with fluoride ion acceptor: