Discuss the trends in chemical reactivity of group 15 elements.
Hydrides: All elements of group 15 form gaseous hydrides of the type MH3.
In all the hydrides the central atom is sp3 hybridized and their shape is pyramidal due to presence of lone pair of electrons.
(a)The basic strength of the hydrides decreases as we move down the group.
Thus, NH3 is the strongest base.
NH3 > PH3 > AsH3 > SbH3
(b)The thermal stability of the hydrides decreases as the atomic size increases, i.e., the M – H bond strength decreases which means reducing character increases.
(c)In the liquid state, the molecules of NH3are associated due to hydrogen bonding. The molecules of other hydrides are not associated.
(d)NH3 is soluble in water whereas other hydrides are insoluble.
(e)All the hydrides, except NH3, are strong reducing agents and react with metal ions (Ag+, Cu2+, etc.) to form phosphides, arsenides or antimonides.
Halides: The elements of group 15 form two series of halides MX3 and MX5.
(a)All the elements of the group form trihalides. The ionic character of trihalides increases as we move down the group. Except NCl3 all the trihalides are hydrolysed by water. This is due to the absence of d-orbitals in nitrogen.
(b)PF3 is not hydrolysed because fluorine being more electronegative than oxygen forms more stable bonds with phosphorus than P – O bonds.
(c)N cannot form NX5 because of non-availability of rforbitals. Bi cannot form BiX3 because of reluctance of 6s electrons of Bi to participate in bond formation.
(d)The hybridisation of M in MX3 is sp3 and shape is pyramidal. M in MX5 is sp3 as hybridised and shape is trigonal pyramidal. The axial bonds in MX5 are weaker and longer, So MX5 are less stable and decompose on heating eg:
Oxides:
(a)Nitrogen forms a number of oxides. The rest of the members (P, As, Sb and Bi) of the group form two types of oxides : E203 and E2O5.
(b)The reluctance of P, As, Sb and Bi to enter into pπ -pπ multiple bonding leads to cage structures of their oxides and they exist as dimers, E4O6 and E5O10.
(c)The basic nature of die oxides increases with increase in atomic number of the element. Thus, the oxides of nitrogen (except N20 and NO), P (III) and As (III) are acidic, Sb (III) oxide is amphoteric and Bi (III) oxide is basic.
Name three oxoacids of nitrogen. Write the disproportionation reaction of that oxoacid of nitrogen in which nitrogen is in +3 oxidation state.
Explain why inspite of nearly the same electronegativity, nitrogen forms hydrogen bonding while chlorine does not.
In the preparation of H2S06 by contact process, why is S03 not absorbed directly in water to form H2S04?
Write a balanced chemical equation, for the reaction showing catalytic oxidation of NH3 by atmospheric oxygen.
Explain why does the stability of oxoacids of chlorine increase in the order given below:
HClO < HClO2 < HClO3 < HClO4
Phosphorus forms a number of oxoacids. Out of these oxoacids phosphinic acid has strong reducing property. Write its structure and also write a reaction showing its reducing behaviour.
Why is BiH3 the strongest reducing agent amongst all the hydrides of group 15 elements? (C.B.S.E. 2013)
Why does nitrogen show catenation properties less than phosphorus ? (C.B.S.E. Foreign 2009)
How is nitrogen prepared in the laboratory? Write the chemical equations of the reactions . involved.
Give the formula and describe the structure of a noble gas species which is isostructural with: (i) ICI4– (ii) IBr2– (iii) Br03–
Reduction potentials of some ions are given below. Arrange them in decreasing order of oxidizing power.
Which of the following statements are correct?
(a) Among halogens, radius ratio between iodine and fluorine is maximum.
(b) Leaving F – F bond, all halogens have weaker X – X bond than X – X’ bond in interhalogens.
(c) Among interhalogen compounds maximum number of atoms ate present in iodine fluoride.
(d) Interhalogen compounds are more reactive than halogen compounds.
Which of the following statements are correct?
(a) All three N – O bond lengths in HNO3 are equal.
(b) All P – Cl bond lengths in PCl5 molecule in gaseous state are equal.
(c) P4 molecule in white phosphorus have angular strain therefore white phosphorus is very reactive.
(d) PCl5 is ionic in solid state in which cation is tetrahedral and anion is octahedral.
Which of the following statements are correct?
(a) S – S bond is present in H2S2O6.
(b) In peroxosulphuric acid (H2SO5) sulphur is in +6 oxidation state.
(c) Iron powder along with Al2O3 and K2O is used as a catalyst in the preparation of NH3 by Haber's process
(d) Change in enthalpy is positive for the preparation of SO3 by catalytic oxidation of SO2.
Why is nitric oxide paramagnetic in gaseous state but the solid obtained on cooling is diamagnetic?
Nitric acid forms an oxide of nitrogen on reaction with P4O10. Write the reaction involved. Also write the resonating structures of the oxide of nitrogen formed.
PCl5 reacts with finely divided silver on heating and a white silver salt is obtained, which dissolves on adding excess aqueous NH3 solution. Write the reactions involved to explain what happens.
Assertion (A): HNO3 makes from passive.
Reason (R): HNO3 forms a protective layer of ferric nitrate on the surface of iron.
What happens when white phosphorus is heated with concentrated NaOH solution in an inert atmosphere of CO2?
The HNH angle value is higher than HPH, H AsH and HSbH angles. Why?
(Hint: Can be explained on the basis of sp3 hybridisation in NH3 and only s-p bonding , between hydrogen and other elements of the group).
Justify the placement of O, S, Se, Te and Po in the same group’of the periodic table in terms of electronic configuration, oxidation state and hydride formation.
Knowing the electron gain enthalpy values of O—>O– and O—>O2- as -141 and 702 kJ mol-1 respectively, how can you account for the formation of a large number of oxides having O2- species and not O–?
