Chemical Bonding Exercise # 4

Exercise # 4 1. [Subjective Type Questions] What type of bonding is expected between. (a) a metal and a non-metal (b) two non-metal 2. Compare the bond angle in O3 and SO2. 3. Write down the resonating structures for SO42– and NO3–. 4. Identify the type of overlapping in N–H bond in N2H4 molecule? 5. One of the first drugs to be prepared for use in treatment of acquired immuno deficiency syndrome (AIDS) was azidothymidine (AZT). O || C H CH3 C || C .. C H O N H O C CH H C H H H C—C .. N || H O N || N || N H (a) How many carbon atoms have sp3 hybridisation ? (b) How many carbon atoms have sp2 hybridisation ? (c) How many nitrogen atoms (central atom not terminal) have sp hybridisation ? (d) How many  bonds are in the molecule ? 6. Draw the structure of the following compounds. Clearly indicate the number of bond pairs and lone pairs involved on central atom. Write (i) number of bond pairs and lone pairs on the central atom (ii) the shape of the molecules (iii) hybridization of the central atom. (a) SF4 (b) XeOF4 7. Assuming that all the four valency of carbon atom in propane pointing towards the corners of a regular tetrahedron. Calculate the distance between the terminal carbon atoms in propane. Given, C—C single bond length is 1.54 Å. 8. There will be three different flourine-flourine distances in molecule F2C=C=C=CF2. Assuming ideal bond angles for a particular hybridisation (assume no distortion due to double bonds), find out the two smaller flourine-flourine distances (in pm). (Given that C–F bond length = 134 pm, C = C bond length = 134 pm, 9. 3 = 1.7) Draw orbital overlap diagram for the cases given below. consider internuclear axis as y-axis . Also classify them as ,, if bond is formed by their overlap (a) s and py (b) dxy and py (c) s and pz (d) px and px (e) pz and pz (f) dxz and dxz CHEMICAL BONDING 10. SF4 and SF6 are known but OF4 and OF6 are not. Explain only in one or two lines. 11. Why electrovalent compounds do not show stereoisomerism? 12. 13. The cynate ion (OCN)– form stable series of salts, but many fulminates (CNO)– are explosive. Explain. BF3 and graphite both are coplanar having sp2 hybridisition yet graphite is a conductor. Explain. 14. Draw structures for the polymeric (BeH2)n and (BeCl2)n. Explain in brief why the hydride bridge in (BeH2)n is considered to be electron deficient but not the halide bridge in (BeCl2)n? 15. Find number of bonds in : (a) P3O105– with bond order = 16. The number of P–S bonds and P– P bonds in P 4S3 are x and y respectively. The number of –bonds in P 4O10 is z. Fill answer in bubbles as xyz. 17. Discuss the bond order and magnetic nature of following species. NO, NO+ NO2+ , NO – 18. (a) Number of shared ‘O’ atoms in [Si6O18]12– cyclic silicate. (b) Number of S – S bond present in H2S4O6 (tetrathionic acid). (c) Number of P – P bonds in P4S3 molecule. (d) Maximum number of equivalent N – O bonds in N2O5 (g). (e) Number of S – O – S bonds in cyclic trimer of SO3. 19. Answer the following questions with respect to the compound NO[BF4]. (P) Bond order of the part underlined. (Q) Total number of  bonds in the compound. (R) Total number of  bonds in the compound. (S) Number of hybrid orbitals involved in the hybridisation of boron. 20. (a) Number of unpaired electrons in O2[AsF6]. (b) Bond order of O – O bond in Na2O2 (c) Number of polar bonds in H2O2 (d) Number of  bonds in carbon suboxide molecule. (e) Number of non bonded electron pairs is present in N(SiMe3)3. Fill your answer in the box provides : 21. Answer the following questions about the structure of the dimer of phosphorus pentaoxide. (i) The number of P – O linkages which have bond length equal to 1.43Å. (ii) The number of covalent bonds which have bond length equal to 1.60Å. (iii) The number of P – O – P linkages. (iv) The number of lone pair(s) of electrons on each phosphorus atom. (i) (ii) (iii) (iv ) 4 3 (b) S2O72– with bond order = 5 3 22. Find number of 3c–2e bond in (BeH2)n 23. In trimethylamine, the nitrogen has a pyramidal geometry whereas in trisilylamine N(SiH3)3 it has a planar geometry. Explain? Out of trimethylamine and trisilyamine which one is more basic and why ? 24. O2, N2 are colourless gases but Cl2, Br2, I2 are coloured gases. Explain on the basis of M.O. theory. 25. Draw the molecular orbital (both bonding and antibonding) and identify the number of nodal planes in the following combination of atomic orbitals with z as internuclear axis : dyz and dyz 26. Draw structure of boron nitride and express the hybridisation of B and N . Will it conduct electricity like graphite? 27. Arrange the following compounds in the order of increasing ionic character : KI, AlP, CaS, MgO. 28. The M.P. of NaCl is higher than that of AlCl3. Explain. 29 Alkali metals impart colour to the flame. Explain. 30. Radii of the following cations are nearly same. Arrange them in the increasing order of polarising power : (i) Mg2+ , Fe2+, Ni2+, Zn2+ 31. Arrange the following in increasing order of melting points. (i) XeF2, XeF4, XeF6 32 (ii) Ga3+, Fe3+, Al3+ (ii) TiCl2, TiCl3, TiCl4 (iii) NaCl, MgCl2, AlCl3 Out of the given species, which one has highest polarising power and why. Na+, Ca2+, Mg2+, Al3+ 33. HF forms H-bonding with acetylene while it is a non polar molecule. Explain. 34. It is said that two –OH groups present on a carbon are unstable. But choral hydrate CCl3CH(OH)2 is fairly stable. Explain. 35. Thio - ethers have higher boiling point than ethers. Explain. 36. Two atoms A and B have electronegativities as 2.1 and 3.5. These two atoms are covalently single bonded and compound AB has experimental dipole moment equal to 1.4 D. Calculate AB bond length in Å(Use Hanny smith formula for calculation of percentage ionic character). 37. Dipole moment of LiF was experimentally determined and was found to be 6.0 D. Calculate percentage of ionic character in LiF molecule. LiF bond length is 2.5 Å. 38. The gaseous metallic chloride (MCl type) molecule has a measured dipole moment of 9.0 D, which indicates that it is a very polar molecule. The separation between the nuclei in this molecule is 2.25 × 10 –8 cm. Calculate the percentage ionic character in KCl molecule. [1.6 x 10–19 , C = 4.8 x 10–10 esu] CHEMICAL BONDING 39. The bond angle in H2S is 97º and its dipole moment is 1.5 D. The S – H bond distance is 0.15 nm. Therefore, approximate percentage ionic character of S – H bond is (neglect the effect of dipole moment of lone pair on sulphur atom in H2S). (Given [cos 97º = – 0.12] and 0.88 = 0.94) 40. Arrange the following in the increasing order as stated below : (i) Polarisibility (for the same cation) : O2–, F–, N3– (ii) Covalent character : LiI, LiBr, LiF (iii) H-bond strength : P: –O–H----- Q: H----- R: – S: –O–H ----- H----- (iv) Boiling point : NH3, AsH3, PH3 41. Which among the following will have zero dipole moment. H2O, CO2, BF3, NH3 42. Out of the given bonds, which one is most polar? (a) C–O 43. (b) C–F (c) O–F (d) N–F Answer the following questions : (P) The number of p-d bonds in S3O9. (Q) The bond order of the underlined species ; NOHSO4. (R) The number of vacant hybrid orbitals which participate in the formation of 3-centre 2 electron bonds i.e., banana bonds in diborane structure. (S) The number of intramolecular H-bonds formed in a molecule of chloral hydrate. 44. The dipole moment of HBr is 2.60 × 10–30 Cm and the inter-atomic distance is 1.41 Å. What is the per cent ionic character of HBr ? 45. A diatomic molecule has a dipole moment of 1.2 D. If bond length is 1.0 Å, what percentage of an electronic charge exists on each atom. 46. Arrange the following (i) N2, O2, F2, O+2; in increasing order of bond dissociation energy. (ii) O, S, F, CI, N; in increasing strength of hydrogen bonding (X – H – – – X). (iii) N3–, BF3, NH3, XeF4. in increasing bond angle. 47. The dipole moment of a molecule is really the vectorial sum of the individual bond moment present in it. To compute the dipole moment it is necessary to find out the values of various bond moment. in the following table dipole moment of different bonds are as given. Bond H Bond moments 0.4 D C C CI 1.5 D C O 2.5 D The group moments of few group as given Group direction of dipole Dipole moment NO2 toward N 4D OH towards O 1.6 D CN toward N 3.8 D CH3 away from CH3 0.4 D (i) In CH3CCI3 (I), CHCI3 (II) and CH3CI (III) the normal tetrahedral bond angle is maintained. Also given cos 70.5º = 1 . Find dipole moments of the given compounds. (given due to – I effect of CI, the Bond moment of 3 H—C bond directed toward the H in CHCI3) (ii) In the acetone molecule considering the normal planer structure, find the observed dipole moment of acetone molecule. 48. Explain the H-bonding in crystalline NaHCO3 and KHCO3 ?