6. PROPUESTA : MODIFICACIÓN DEL MARCO TEÓRICO COBIT . 54
6.3. Mapeo de las Metas TI y los Procesos Relacionados con las TI
6.3.2. Construcción, Adquisición e Implementación
PARIKRAMA - I
Q.1 Why the atoms of noble gases do not react with other atom to form compounds ?
Q.2 Why ? The ionic bond is called a non directional but covalent bond is called a direction bond.
Q.3 Why MgO is more stable than NaCl ? Q.4 Why the NaCl is more stable than CsCl ?
Q.5 Why ionic compound do not conduct electricity when they are in the solid state ? or
Q.6 Why the ionic solid conduct electricity when they are in water solution or in molten state ? or
Q.7 Why the ionic solids are soluble in polar solvent like H2O. ? or
Q.8 Explain the solubility of ionic solid in a polar solvent like water ? or
Q.9 Why ? An ionic solid dissolve in polar solvent ? or
Q.10 Explain why ionic solids are not soluble in non polar solvents ? Q.11 Why elements show variable covalency ?
Q.12 Why the covalent compounds are consist of discrete molecules ? Q.13 Why some covalent compounds ore good conductor of electricity ? Q.14 Why covalent solid are soluble in non-polar solvents ?
Q.15 Why covalent solids having the giant molecules are insoluble in all the solvents ? Q.16 Why the covalent compound neither hard not brittle ?
Q.17 Why the reaction of covalent compound are slow ?
Q.18 Why ionic compounds are not show isomerism but covalent compounds show this phenomenone ? Q.19 Why an alloy is hard then pure metal ?
Q.20 Why metals are highly tensile ?
Q.21 Why metallic bond is weaker than a covalent bond ? Q.22 Why only O, N and F are capable of forming H –bonds ? Q.23 Why NH3 is better electron donner than PH3, H2S & H2O ? Q.24 Why metals have high density ?
Q.25 Why the alkaline earth metals are harder than alkali metals ? Q.26 Explain the hardness sequence Li > Na > K ?
Q.27 In ordinary conditions water exist as liquid but H2Se and H2Te as gases why ?
Q.28 Explain the following sequence for boiling point ? He < Ne < Ar < Kr < Xe < Rn
Q.29 Explain how can a molecule has less energy and high stability than isolated atoms ? Q.30 Why – bond is weak than – bond ?
Q.31 Why a molecule is more stable in terms of energy than the uncombined atoms ?
Q.32 Why sodium chloride does not conduct electricity in solid state but does so in molten state ? Q.33 Why H2O is liquid while H2S is a gas at ordinary temperature ?
Q.34 Why BCl3 and BF3 are non polar ?
Q.35 Why BeF2 and BF3 are stable though Be and B have less than 8 electrons ? Which one is more stable?
Q.36 Why the repusion between non bonded orbitals is greater than between the bonded orbitals ? Q.37 Why Valency of oxygen is generally two whereas sulphur shows valency of two, four and six ? Q.38 Why anhydrous HCl is bad conductor but in aqueous medium, it is good conductor of current ? Q.39 Why diamond is a hard solid with a very high melting point but a non-conductor of electricity ? Q.40 Why AlCl3 is largely covalent while AlF3 is largely ionic ?
Q.41 Arrange the following bonds in increasing order of strength C – C, Ge – Ge, Si – Si
Q.42 F2 and Cl2 are gases, Br2 is liquid and I2 is solid why ? Q.43 CO2 is gas but SiO2 is solid. Why ?
Q.44 NH3 can be liquefied easily but PH3 is not. Why ?
Q.45 What is the increasing order of ionic character in HF, HCl, HBr and HI, Explain ? Q.46 What is the increasing order of ionic character in H2O, H2S and H2Se, Explain ? Q.47 What is the decreasing order of ionic character in NCl3 and PCl3, Explain ? Q.48 NF3 is less stable than NCl3. Why ?
Q.49 Why is PCl5 unstable ?
PARIKRAMA -II
Q.1 Why KHF2 is exist but KHCl2 is not ?
Q.2 Why Co+3 ion is form with great difficulty but Fe+3 is not ?
Q.3 Why an ionic solid do not exist as individual neutral independent molecules ? Q.4 Why NaCl have less boiling point than SiCl4 ?
Q.5 Explain why Cu+ cation polarises the anions more strongly than Na+ cation even both have +1 charge?
Q.6 Why Ag+ (cation) 4s2p6d10 has greater polarising power than K+ (cation) 3s2p6 ? Q.7 Why Li+ compounds are soluble in non polar solvent but not in polar solvents ? Q.8 Explain the following sequences of solubility ?
AlF3 > AlCl3 > AlBr3 > Al I3
Q.9 Why co-ordinate bond is called semi polar bond ?
Q.10 Why H – atom alone is not capable of forming hydrogen bond ?
Q.11 Why metals have intermediate melting and boiling point as compared to those of covalent and ionic compounds ?
Q.12 Explain why melting point of o-nitrophenol is lesser than m and p-isomers ? or
o-nitrophenol is volatile in steam and less soluble in water than the other two isomers ?
Q.13 Boiling point of hydrides of VA, VIA & VIIA decrease from top to bottom but NH3, H2O & HF show a sudden increase why ?
Q.14 Explain why glycerol (CH2(OH) – CH(OH) – CH2(OH)) have more viscosity, high heat of vaporisation and high dielectric constant ?
Q.15 The density of ice is less then that of water or ice floats over water. Explain ?
Q.16 Methanoic acid, HCOOH, has one carbon-oxygen bond of length 123 pm, and another of 136 pm.
Which bond has which length ?
Q.17 Both carbon-oxygen bonds in the methanoate ion, HCOO–, have the same length (127 pm). What does this tell about bonding ?
Q.18 Water can react with hydrogen ion to make the oxonium ion, H3O+. What is present in water molecule that allows it to react with a hydrogen ion ? Describe the bonding in the oxonium ion. Draw a dot and cross diagram for the molecule ?
Q.19 Why MgCl2 is linear but SnCl2 is angular ? Q.20 Why NCl5 does not exist while PCl5 does ? Q.21 Why Lead prefers to form divalent compounds ?
Q.22 Why CH4, NH3 and H2O contain same number of electron but their shapes are different ? Q.23 Why Calcium fluoride is more ionic than CaI2 ?
Q.24 Why Ammonium salts are much more soluble in water than the corresponding sodium salts ?
Q.25 Why Carbon has two electrons unpaired in the outer most, but it forms tetravalent in organic com-pounds ?
Q.26 The electronegativities of nitrogen and chlorine are same but NH3 exists as liquid whereas HCl as gas.
Why ?
Q.27 Although CO2 has no dipole moment, SO2 and H2O have considerable dipole moments. Why?
Q.28 Nitrogen trifluoride (NF3) and ammonia (NH3) have identical shape and a lone pair of electrons on nitrogen and further the electronegativity difference between the elements is nearly the same but the dipole moment of NH3 is very high in comparison to NF3. Why ?
Q.29 Why Three carbon-oxygen bonds are equal in carbonate ion ? Q.30 Why NF3 is weaker base than NH3, NCl3, NBr3 and NI3 ? Q.31 Why BaSO4 is insoluble in water ?
Q.32 Why compounds of normal elements are diamagnetic ? Q.33 Why IF7 is exist but ClF7 is not.
Q.34 Which among the following has highest boiling point and why ? H2, He, Ne, Xe, CH4
Q.35 At room temperature, NO2 gas is paramagnetic in nature. When it is cooled below 0ºC acquires diamagnetic behaviour. Explain this observation on the basis of structure ?
Q.36 Explain why the super oxides KO2, RbO2 and CsO2 are paramagnetic ?
Q.37 NH4+ has bond angle identical to CH4 but NH3 has different bond angle; explain with proper reasoning ? Q.38 Explain why ClF2– is linear but ClF2+ is bent molecular ion ?
Q.39 Ether and water have same hybridization at oxygen but they have not same bond angle. Why ?
Q.40 In trimethylamine, the nitrogen has a pyramidal geometry whereas in trisilylamine N(SiH3)3 it has a planar geometry. Account for this fact.
Q.41 Carbon has maximum covalency of four. Explain the covalency of carbon in given compound.
Q.42 Which among the following will have the highest melting point ? PH3, NH3, (CH3)3N
Q.43 Discuss the hybridization and shape of the molecule . Indicate whether the molecule is polar or non-polar.
Q.44 The dielectric constant of H2O2 is more than that of H2O, but H2O2 is not a good solvent. Why ? Q.45 What is the increasing order of bond angle in OF2 and Cl2O ?
Q.46 Why in hydrogen & vander waal interaction bonding atoms do not lose their identity ? Q.47 AgCl is white, AgBr is yellow & AgI is deep yellow. Why ?
Q.48 Why CCl4 does not get hydrolised but SiCl4 get hydrolised.
Q.49 Why SF6 is exist but OF6 is not ?
SOLUTIONS (Parikrama– I)
Ans.1 Because the outer most electron configuration of the atoms of noble gas is a stable configuration of 8 electron which is also called octet.
Ans.2 Because in ionic bond, an ion can attract other opposite charged ions from any direction and extends equally in all directions so the nature of ionic bond is non-directional, but on the other band a covalent bond is formed by the proper overlapping of orbitals so it have directional character.
Ans.3 A/c to the force of attraction between constituent ions.
F q q d
q q rA rB
1 2 2
1 2
( –)2
The electric charge on doubly charged Mg+2 and doubly charged O–2 ion in Mg+2O–2 ionic crystal is 4 times greater than between monovalent Na+ and Cl– ions in Na+ Cl–
Ans.5 Because Na+ is smaller than Cs+ ion so the force of attraction between Na+Cl– ion in NaCl is higher than attraction between Cs+Cl– in CsCl. So NaCl have high lattice energy then CsCl and have greater stability.
Ans.6 Due to the following two reasons
-(i) Unstable configuration of the core (Kernal) (ii) Inert electron pair effect.
Ans.7 Because in the crystal lattice the cation and anions are tightly held together with each other so the ions therefore ; can not move freely to any large extent when an electric current is passed through the ionic solids.
Ans.8 Because when the ionic compound goes in to the molten state. The kinetic energy of ions becomes so high that the attractive forces acting between the ions are over come so the arrangement of ions in crystal is destroyed and the ions become free to move in liquid medium.
Ans.9 The electrostatic force between cation and anions is reduced by the high dielectric constant value of polar solvent. Ions are move freely and interact with solvent molecule to form the solvated ions.
Ans.10 The water molecule is a dipole and hence the positive end of water dipole interact with the negative ion of the ionic solids and the negative ion of the ionic solids and the negative end of the dipole interacts with the positive ion of the same ionic crystals.
Ans.11 For an ionic solid to dissolve in a polar solvent the solvation energy of the solvent must be greater than the lattice energy of the ionic solid so that the solvation energy may overcome the lattice energy.
Ans.12 Because the force of attraction between adjacent covalent molecules is weak.
Ans.13 Because these compounds having the layer lattices (graphite) and they have a free electrons which are good conductors of electricity. In such solids electrons can pass from one layer to the other and thus current can be carried.
Ans.14 Due to the similarity in covalent nature of the molecule of the solute and solvent their solubility is based on the principle like dissolves like.
Ans.15 This is due to the fact because due to their big size, are not able to interact with the solvent molecule.
Ans.16 Because there are weak forces holding the molecules in solid crystal. A molecular layer in the crystal easily slips relative to other adjacent layer and there are no forces of repulsion between the other layers like those in ionic compound.
Ans.17 Because there are no strong electrical force is present to speed up the reaction between molecules.
Ans.18 Because ionic bonds are not rigid and non-directional but covalent bond are region and directional.
Ans.19 Because if an alloying metal is added to a metal. The structural homogeneity of the principal metal is disturbed and hence the resulting allow is hard and brittle.
Ans.20 It is due to the great attraction between the positive metal ion and the mobile electron.
Ans.21 Due to the presence of the delocalised, electron (mobile electron) the attraction force between valence electron and the nuclei is weak but on the other hand is covalent bond due to the presence of localised electron there is more attraction between valence electron and nuclei is develop and thus covalent bond is stronger than metallic bond.
Ans.22 It is due to their high electronegativity and small atomic size.
Ans.23 It is due to the presence of vacant d-orbitals in PH3 and H2S. In H2O due to more electronegativity of O than N. Electron losing capacity of H2O will be less than NH3.
Ans.24 This is due to fact that the metal bond keeps the metal atoms closely packed in the metallic crystal.
Ans.25 Because the strength of metallic bond increases with increase of valence electrons and we know that alkaline earth metals have two and alkali metals have one valence electron.
Ans.26 Because the size of Li+, Na+ and K+ ion is in the order.
Li+ < Na+ < K+
Ans.27 Due to the high electronegativity of O-atom than S, Se and Te. H2O molecule associate to form a polymerised molecule while H2S, H2Se and H2Te cannot do so.
Ans.28 With increase of vander wall forces the boiling point or melting point of a substance also increase.
Ans.29 Because the overlapping of orbital involves a release of energy. This show that the formation of cova-lent bond is always accompanied by evolution of energy and thus stablilises the molecules.
Ans.30 Because -bond is formed by the side to side overlapping between two p-orbital which much less effective than -bond which formed by the head to head overlapping between p-orbitals.
Ans.31 When the atoms combined together to form molecule there is always release of energy. Thus potential energy of molecule is less than that of uncombined atoms and therefore, the molecule is more stable.
Ans.32 Because solid sodium chloride has crystalline structure in which the ions are not free to move the ion become mobile when it is in molten state and thus the electricity can be conduct.
Ans.33 Because oxygen has high electronegativity than sulphur. As a result, H2S forms hydrogen bonding so molecule of water come nearer to each other through hydrogen bonding. This results in higher boiling point of water and hence it is a liquid.
Ans.34 Both are triangular and symmetrical molecules their dipole moment are zero.
Ans.35 The stability is explained by symmetrical linear structure of BeF2 and triangular planer structure of BF3. BeF2 is more stable because of its greater bond angle (180º).
Ans.36 The non-bonded orbitals relatively occupy space compared to the bonded orbitals and thus repulsion are greater.
Ans.37 Because there are no orbitals in oxygen and hence it can not extend it/s covalency but vacant d-orbitals are present in S are paired d-orbitals can be unpaired by shifting electrons to d-orbital so either making four orbitals singly occupied or six orbitals singly occupied showing valency 4 or 5 besides ?
Ans.38 HCl is a covalent compound and in gaseous state it does not conduct current. In water however it react to form ions, HCl + H2O H3+O + Cl– and thus conduct current.
Ans.39 Because diamond is a giant molecule-three dimensional figure as every carbon is sp3 hybridised so one carbon atom is linked to four other carbon atoms tetrahedrally. Due to continuous covalent bonding all the atoms are held very closely are strongly as a result diamond is a very hard solid with a very high MP.
It is non conductor as free electrons are not available.
Ans.40 Due to large size of Cl– ion than F– ions there is greater degree of distortion in AlCl3. Ans.41 Ge – Ge < Si – Si < C – C
Bigger is the atomic size lower is the bond strength.
Ans.42 Intermolecular distance is high in gaseous state, low in solid state and inter mediate in liquid state. When molecular weight increases, vander waal's forces also increases. So F2 and Cl2 are gases due to the weak vander waals forces and I2 is solid.
Ans.43 CO2 has only weak vander waals forces but in SiO2, one silicon atom is surrounded by four oxygen atoms tetrahedrally forming macromolecular string So SiO2 is solid.
Ans.44 Because H-bonding present in NH3, while PH3 is non polar due to same value of electronegativity of P and H.
Ans.45 HI < HBr <HCl < HF.
It is because that the electronegativity difference is maximum in H and halogen atom.
Ans.46 H2Se < H2S < H2O. This is because the increasing electronegative difference between H – atom and O, S and Se atom.
Ans.47 PCl3 > NCl3, Because electronegativity difference of P and Cl is greater than N and Cl.
Ans.48 NH3 is more polar than NCl3 – SO bond energy of N – F will be higher.
Ans.49 String of PCl5 is unsymmetrical because the value of bond angles are different.
SOLUTIONS (Parikrama – II)
Ans.1 HF2– is formed by H-bonding which formes KHF2 with K+ while H-bond is not formed due to low electronegativity of Cl– thus KHCl2 is not exist
Ans.2 Increasing the nuclear charge in an atom tend to prevent the removal of electron from a lower energy level. As Co atom forms Co+3 ion with great difficulty because 3d electrons are more firmly retained by cobalt nucleus with positive charge equal to +27 which one unit higher than that on iron nucleus (= +26) Fe(26) 3s2p6d6, 4s2, Fe+2(24) 3s2p6d6, Fe+3(23) 3s2p6d5
Co(27) 3s2p6d7, 4s2, Co+2(25) 3s2p6d7, Co+3(24) 3s2p6d6
Ans.3 Because in crystal lattice a large number of cation and anion attract each other due to electro static force of attraction which extends in all directions. So in order to occupy minimum space the ions arrange themselves systemetically in an alternating cation-anion pattern thus we see that an ionic crystal consist of three dimensional solid string.
Ans.4 NaCl is ionic and SiCl4 is covalent bond.
Ans.5 According to their electronic configuration Cu+(3s2p6d18)have 18 electron in its valence shell but Na+(2s2p6) have 8 electron in its valence shell so the d-electron of the 18 electron shell shield the nuclear charge of cation less effectively.
Ans.6 same reason (Q. 5)
Ans.7 Because Li+ cation has a maximum polarising power due to its small size.
Ans.8 So AlF3 > AlCl3 > AlBr3 > AlI3. Increase the covalent character lower the solubility. The AlF3 have maximum ionic character thus it have maximum solubility.
Ans.9 Because it is formed by these two steps.
Ist step – In this the doner (A) transfer 1 electron of it lone pair to the acceptor (B) so A develop unit positive & B develop unit negative charge. This step is similar to the formation of ionic bond.
A + B A + B –
IInd step – In this the two electrons one each with A+ & B– are shared by both the ion in this step is similar to the formation of covalent bond.
A B A + B –
Thus we say that a co-ordinate bond is equivalent to a combination of an electrovalent bond (polar bond) and a covalent bond (non polar bond) so it is called semi polar bond.
Ans.10 Because H-atom has small size with only one electron in its Ist energy level, when this electron is taken away, the proton (H+) left behind which can easily manage between two electronegative atoms bringing them closer together by creating electrostatic force.
Ans.11 This is due to the reason that the attractive forces (metallic bond) in metallic crystal are intermediate between those in covalent and ionic compound.
Ans.12 Because in o-nitrophenol a six membered ring (chelation) is formed by intramoleculer H-bond so it have different properties from those of other isomers. Because this type of bonding is not possible in m
& p-isomer because of the size of the ring that would result.
& p-isomer because of the size of the ring that would result.