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Question
Arrange the following.(i) CaH2, BeH2 and TiH2 in order of increasing electrical conductance.
(ii) LiH,NaH and CsH in order of increasing ionic character.
(iii) H−H,D−D and F−F in order of increasing bond dissociation enthalpy.
(iv) NaH,MgH2 and H2O in order of increasing reducing property.
(i) CaH2, BeH2 and TiH2 in order of increasing electrical conductance.
(ii) LiH,NaH and CsH in order of increasing ionic character.
(iii) H−H,D−D and F−F in order of increasing bond dissociation enthalpy.
(iv) NaH,MgH2 and H2O in order of increasing reducing property.
(ii) LiH,NaH and CsH in order of increasing ionic character.
(iii) H−H,D−D and F−F in order of increasing bond dissociation enthalpy.
(iv) NaH,MgH2 and H2O in order of increasing reducing property.
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Solution
(i) Ionic compounds conduct electricity whereas covalent compounds does not.
BeH2 is a covalent hydride and does not conduct electricity. CaH2 is an ionic hydride and conducts electricity in molten state. TiH2 is metallic in nature and conducts electricity at room temperature.
Hence, the increasing order of electrical conductivity is BeH2<CaH2<TiH2.
(ii) The ionic character of bond depends on electronegativity difference between two atoms. When the electronegativity difference is larger, the ionic character is smaller. On moving down the group of alkali metals, the electronegativity decreases from Li to Cs. Hence the ionic character increases in the order LiH<NaH<CsH.
(iii) Bond dissociation energy depends on bond strength. Bond strength depends on the attractive and repulsion forces present in a molecule.
Due to higher nuclear mass of D2, the attraction between nucleus and bond pair in D-D is stronger than in H-H. This results in greater bond strength and higher bond dissociation enthalpy. Thus, the bond dissociation enthalpy of D−D is higher than that of H−H.
The bond dissociation enthalpy of F-F is minimum as the repulsion between the bond pair and lone pairs of F is strong.
Hence, the increasing order of bond dissociation enthalpy is F−F<H−H<D−D.
(iv) NaH is an ionic hydride and can easily donate its electrons. It is most reducing. MgH2 and H2O are covalent hydrides. H2O has lower reducing power than MgH2 as its bond dissociation energy is higher.Hence, the increasing order of the reducing property is H2O<MgH2<NaH.
BeH2 is a covalent hydride and does not conduct electricity. CaH2 is an ionic hydride and conducts electricity in molten state. TiH2 is metallic in nature and conducts electricity at room temperature.
Hence, the increasing order of electrical conductivity is BeH2<CaH2<TiH2.
(ii) The ionic character of bond depends on electronegativity difference between two atoms. When the electronegativity difference is larger, the ionic character is smaller. On moving down the group of alkali metals, the electronegativity decreases from Li to Cs. Hence the ionic character increases in the order LiH<NaH<CsH.
(iii) Bond dissociation energy depends on bond strength. Bond strength depends on the attractive and repulsion forces present in a molecule.
Due to higher nuclear mass of D2, the attraction between nucleus and bond pair in D-D is stronger than in H-H. This results in greater bond strength and higher bond dissociation enthalpy. Thus, the bond dissociation enthalpy of D−D is higher than that of H−H.
The bond dissociation enthalpy of F-F is minimum as the repulsion between the bond pair and lone pairs of F is strong.
Hence, the increasing order of bond dissociation enthalpy is F−F<H−H<D−D.
Due to higher nuclear mass of D2, the attraction between nucleus and bond pair in D-D is stronger than in H-H. This results in greater bond strength and higher bond dissociation enthalpy. Thus, the bond dissociation enthalpy of D−D is higher than that of H−H.
The bond dissociation enthalpy of F-F is minimum as the repulsion between the bond pair and lone pairs of F is strong.
Hence, the increasing order of bond dissociation enthalpy is F−F<H−H<D−D.
(iv) NaH is an ionic hydride and can easily donate its electrons. It is most reducing. MgH2 and H2O are covalent hydrides. H2O has lower reducing power than MgH2 as its bond dissociation energy is higher.
Hence, the increasing order of the reducing property is H2O<MgH2<NaH.Suggest Corrections
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