47. Oxoacids of halogens:
Fluorine forms only one oxoacid HOF( Fluoric( I) acid or hypofluorous acid) due to high electronegativity.
Acid strength: HOCl < HClO2 < HClO3 < HClO4 Reason: HClO4 → H + + ClO4- most stable
Acid strength: HOF > HOCl > HOBr > HOI
This is because Fluorine is most electronegative.
GROUP 18 ELEMENTS:
48. Ionisation enthalpy: They have very high ionization enthalpy because of completely filled orbitals.
Ionisation enthalpy decreases down the group because of increase in size.
49. Atomic radii: Increases down the group because number of shells increases down the group.
50. Electron gain enthalpy: They have large electron gain enthalpy because of stable electronic configuration.
51. Melting and boiling point: Low melting and boiling point because only weak dispersion forces are present.
52. XeF2 is linear, XeF4 is square planar and XeF6 is distorted octahedral. KrF2 is known but no true compound of He Ne and Ar are known.