Chemistry Chemical Properties of Group 18 Elements

### Topics Covered :

● Chemical Properties
● Xenon-Fluorine Compounds
● Xenon-Oxygen Compounds

### Chemical Properties :

=> In general, noble gases are least reactive. Their inertness to chemical reactivity is attributed to the following reasons :

(i) The noble gases except helium color{red}(1s^2) have completely filled color{red}(ns^2 np^6) electronic configuration in their valence shell.

(ii) They have high ionisation enthalpy and more positive electron gain enthalpy.

=> In March 1962, Neil Bartlett, then at the University of British Columbia, observed the reaction of a noble gas.

● First, he prepared a red compound which is formulated as color{red}(O_2^+PtF_6^–). He, then realised that the first ionisation enthalpy of molecular oxygen (1175 kJmol^(–1)) was almost identical with that of xenon (1170 kJ mol^(–1)).

● He made efforts to prepare same type of compound with color{red}(Xe) and was successful in preparing another red colour compound color{red}(Xe^+PtF_6^–) by mixing color{red}(PtF_6) and xenon.

● After this discovery, a number of xenon compounds mainly with most electronegative elements like fluorine and oxygen, have been synthesised.

=> The compounds of krypton are fewer. Only the difluoride color{red}(KrF_2) has been studied in detail.

=> Compounds of radon have not been isolated but only identified (e.g., color{red}(RnF_2)) by radiotracer technique.

=> No true compounds of color{red}(Ar, Ne) or color{red}(He) are yet known.

### Xenon-fluorine compounds :

=> Xenon forms three binary fluorides, color{red}(XeF_2, XeF_4) and color{red}(XeF_6) by the direct reaction of elements under appropriate experimental conditions.

color{red}(undersettext{(xenon in excess)}(Xe(g)) +F_2 (g) overset(673 , text(1 bar))→ XeF_2 (s))

color{red}(undersettext{(1:5 ratio)} (Xe (g)) +2F_2 (g) overset(873K, text(7 bar))→ XeF_4 (s))

color{red}(undersettext{(1:20 ratio)} (Xe (g)) +3F_2 (g) oversettext(573 K, 60−70bar)→ XeF_6 (s))

=> color{red}(XeF_6) can also be prepared by the interaction of color{red}(XeF_4) and color{red}(O_2F_2) at 143K.

color{red}(XeF_4 +O_2F_2 → XeF_6 +O_2)

=> color{red}(XeF_2, XeF_4) and color{red}(XeF_6) are colourless crystalline solids and sublime readily at 298 K.

=> They are powerful fluorinating agents.

=> They are readily hydrolysed even by traces of water. For example, color{red}(XeF_2) is hydrolysed to give color{red}(Xe, HF) and color{red}(O_2).

color{red}(2XeF_2 (s) + 2H_2O (l) → 2Xe (g)+4HF(aq) +O_2 (g))

=> The structures of the three xenon fluorides can be deduced from VSEPR and these are shown in Fig. 7.9.

● color{red}(XeF_2) and color{red}(XeF_4) have linear and square planar structures respectively.

● color{red}(XeF_6) has seven electron pairs (6 bonding pairs and one lone pair) and would, thus, have a distorted octahedral structure as found experimentally in the gas phase.

=> Xenon fluorides react with fluoride ion acceptors to form cationic species and fluoride ion donors to form fluoroanions.

color{red}(XeF_2+PF_5 → [XeF]^+ [PF_6]^(-) ; \ \ \ \ \ XeF_4 + SbF_5 → [XeF_3]^(+) [ SbF_6]^(-))

color{red}(XeF_6 + MF → M^(+) [XeF_7]^(-) \ \ (M = Na , K , Rb text(or) Cs))

### Xenon-oxygen compounds :

=> Hydrolysis of color{red}(XeF_4) and color{red}(XeF_6) with water gives color{red}(XeO_3)

color{red}(6XeF_4 +12 H_2O → 4Xe +2XeO_3 +24 HF +3O_2)

color{red}(XeF_6+3H_2O → XeO_3 +6HF)

=> Partial hydrolysis of color{red}(XeF_6) gives oxyfluorides, color{red}(XeOF_4) and color{red}(XeO_2F_2).

color{red}(XeF_6+H_2O → XeOF_4+2HF)

color{red}(XeF_6+2H_2O → XeO_2F_2+4HF)

=> color{red}(XeO_3) is a colourless explosive solid and has a pyramidal molecular structure (Fig. 7.9).

=> color{red}(XeOF_4) is a colourless volatile liquid and has a square pyramidal molecular structure (Fig.7.9).

Q 3070891716

Does the hydrolysis of XeF_6 lead to a redox reaction?

Solution:

No, the products of hydrolysis are XeOF_4 and XeO_2F_2 where the oxidation states of all the elements remain the same as it was in the reacting state.

### Uses :

=> color{green}("Helium ")

● It is a non-inflammable and light gas.

● It is used in filling balloons for meteorological observations.

● It is also used in gas-cooled nuclear reactors.

● Liquid helium (b.p. 4.2 K) finds use as cryogenic agent for carrying out various experiments at low temperatures.

● It is used to produce and sustain powerful superconducting magnets which form an essential part of modern NMR spectrometers and Magnetic Resonance Imaging (MRI) systems for clinical diagnosis.

● It is used as a diluent for oxygen in modern diving apparatus because of its very low solubility in blood.

=> color{green}("Neon ")

● It is used in discharge tubes and fluorescent bulbs for advertisement display purposes.

● Neon bulbs are used in botanical gardens and in green houses.

=> color{green}("Argon ")

● It is used mainly to provide an inert atmosphere in high temperature metallurgical processes (arc welding of metals or alloys) and for filling electric bulbs.

● It is also used in the laboratory for handling substances that are air-sensitive.

=> There are no significant uses of Xenon and Krypton. They are used in light bulbs designed for special purposes.