REASONING BASED QUESTIONS FROM P-BLOCK ELEMENTS GROUP-15 1 Nitrogen does not form pentahalide although it exhibit +5 oxidation state.

Size: px

Start display at page:

Download "REASONING BASED QUESTIONS FROM P-BLOCK ELEMENTS GROUP-15 1 Nitrogen does not form pentahalide although it exhibit +5 oxidation state."

Anna Opal Wood
6 years ago
Views:

1 REASONING BASED QUESTIONS FROM P-BLOCK ELEMENTS GROUP-15 1 Nitrogen does not form pentahalide although it exhibit +5 oxidation state. Due to absence d-orbitals N can not extend its valency beyond four 2 PH 3 has lower B.pt than NH 3 N is more electronegative than P so in NH 3 there is intermolecular H-bonding hence it has high b.pt 3 NH 3 acts as Lewis base Because N has a lone pair electron so NH 3 acts as a Lewis base 4 NO 2 dimerises NO 2 has an odd electron so it dimerises to pair up electron and to achieve octet configuration 5 NH 3 is stronger base than PH 3 Due to smaller size of nitrogen there is high electron density on nitrogen so electron pair is easily available. 6 PCl 3 fumes in moisture PCl 3 undergoes hydrolysis and gives fumes of HCl. PCl H 2 O H 3 PO 3 + 3HCl 7 All the five P-Cl bonds are not equal in PCl 5 The two axial bonds suffer more repulsion from equatorial bonds and hence are elongated. 8 H 3 PO 2 has reducing character Since it has two P-H bonds 9 H 3 PO 3 is dibasic (diprotic) but H 3 PO 4 is tribasic In H 3 PO 3 only two H atoms are linked to O which are ionisable the third H is attached to P and not ionisable because P is less electronegative. In H 3 PO 4 all the three H atoms are with O and ionisable 10 PCl 5 is ionic in solid state It is due to the following conversion : 2PCl 5 [PCl 4 ] + [PCl 6 ] - 11 NO is paramagnetic in gaseous state but diamagnetic in liquid and solid state NO(g) has odd number of electrons so it is paramagnetic but in liquid and solid state it exists as dimmer so there is no unpaired electron and it will be diamagnetic 12 NCl 3 hydrolysed but NF 3 does not In NCl 3 Cl has vacant d-orbitals to accept the lone pair from H 2 O but in NF 3 F has no d-orbitals NCl 3 + 3H 2 O NH HOCl 13 Nitrogen shows little catenation but phosphorous distinctly shows catenation property Due to smaller size of N there is repulsion between the lone pairs and N-N single bond is weaker than P-P oxidation state of Bi is less stable than +3 Because inert pair effect is very prominent in Bi, so +5 oxidation state is not stable 15 Bi in +5 oxidation state is strong oxidizing agent Because inert pair effect is very prominent in Bi so Bi5+ can be easily converted into Bi3+ 16 NO(nitric oxide) becomes brown when released to air It oxidizes to NO 2 17 NH 3 is a good complexing agent/ NH 3 acts as a ligand It has lone pair of electron on N-atom and can be donated for the coordination bond. 18 Bi 2 O 3 is not acidic The size of Bi 3+ is very large and so there is very weak +ve electric field around it so it does not interact with water to release H + 19 BiH 3 is the strongest reducing agent among the group-15 hydrides Since Bi-H bond is the weakest among pr-15 hydrides so H 2 gas is evolved which is reducing 20 N 2 is less reactive at room temperature Due to having triple bond and hence high bond dissociation energy(946 kj/mol) 21 Bond angle in PH + 4 higher than in PH 3 In PH 3 there is lp-bp repulsion so bond angle is less where as in PH + 4 there is no lp-bp repulsion

2 22 NH 3 has greater bond angle than PH 3 N is more electronegative so it attracts the bond pair electron and hence there is greater bp-bp repulsion in NH 3 and hence greater bond angle 23 R 3 P=O exists but R 3 N=O does not N due to absence of d-orbitals can not form pπ-dπ multiple bond 24 N exists as N 2 but P exists as P 4 Due to smaller size N can form pπ-dπ multiple bonding and exists as discrete N 2 molecule but P can not form pπ-pπ multiple bonding. 25 PCl 5 can not act as reducing agent In PCl 5 P has +5 oxidation state. P has five valence electron in its valence shell so it can not increase its oxidation state beyond +5, so it can not act as reducing agent. 26 Phosphorous is kept under kerosene It is highly reactive and easily catches fire due to air oxidation 27 H 3 PO 3 is syrupy liquid Due to intermolecular H-bonding 28 PH 3 bubbles but NH 3 dissolves in water NH 3 forms H-bonding with water but PH 3 can not form so NH 3 dissolves but PH 3 bubbles out 29 Only a small increase in radius is observed from As to Bi Due to poor shielding effect of d and f obitals. 30 Nitrogen is gas where as phosphorous is solid at room temp. Nitrogen is diatomic molecule having weak van der Walls attraction where as phosphorous is tetra atomic so it has strong van der Walls attraction. 31 N-N bond is weaker than P-P bond Due to shorter bond length there is greater repulsion between lone pairs in N 2 32 Maximum number of covalent bond formed by N is four Because it has three unpaired electrons and one lone pair. 33 P 2 O 5 can not be used for drying ammonia gas. P 2 O 5 is acidic it reacts with ammonia in presence of moisture and form (NH 4 ) 3 PO 4 34 NO 2 is coloured but its dimmer N 2 O 4 is colourless Because NO 2 has unpaired electron so it can absorb light from VR 35 Acidity of oxyacids of nitrogen increases with increase in oxidation number of N Because non metallic character increases with oxidation number 36 White phosphorous is more reactive than red phosphorous White phosphorous consists of discrete P 4 molecules which is tetrahedral so reactive but in red phosphorous the P 4 molecules are linked in extended chain structure so it is less reactive. 37 Phophinic acid ( H 3 PO 4 ) is mono basic / mono protic Only one H atom is linked with O which is ionisable 38 N 2 has higher bond dissociation energy than NO Because N 2 has higher bond order 39 N 2 and CO have same bond order but CO is more reactive CO is polar molecule 40 (CH 3 ) 3 N is pyramidal but (SiH 3 ) 3 N is planar (CH 3 ) 3 N is pyramidal due to sp 3 hybridisation and one lone pair on N but (SiH 3 ) 3 N is planar due to sp 2 hybridisation and its lone pair is donated to vacant d orbital of Si for pπ-dπ overlap 41 The first IE of N is greater than that of O It is due to half filled and hence stable electronic configuration of N 42 HNO 2 disproportionates In HNO 2 the N is in +3 oxidation state which may increase as well as decrease 43 PCl 5 can not act as reducing agent In PCl 5 phosphorous is in +5 oxidation state that is the highest oxidation state of P.

3 GROUP-16 1 Group 16 elements have lower I.E with compare to corresponding group 15 elements Because group 15 elements have stable half filled p-sub shell(ns 2 np 3 ) so electron can not be removed easily 2 H 2 S is less acidic than H 2 Te In H 2 Te there is lower bond energy of H-Te bond due to larger size of Te 3 H 2 S acts as reducing agent while SO 2 acts as both In H 2 S, S has its minimum oxidation state -2 where as in SO 2 it is +4 so it can be decreased up to -2 or increased up to +6, So H 2 S is only reducing but SO 2 is both. 4 H 2 S is acidic while H 2 O is neutral H-S bond is weaker due to larger size of S so proton release easier in H 2 S 5 SF 6 is known but SH 6 does not exist Fluorine is the strongest oxidizing agent so it can oxidizes S to its maximum oxidation state +6, H can not 6 Compound of F & O is fluoride of oxygen not oxide of fluorine F is more electronegative than O 7 SCl 6 is not known but SF 6 is known F is strongest oxidizing agent so it can oxidizes S to its maximum oxidation state +6. Cl can not. Again Cl has larger size so steric repulsion is there in SCl 6 8 SF 6 is used as gaseous electrical insulator It is thermally stable and chemically inert 9 SF 6 is not easily hydrolyzed It is sterically protected by six F atoms hence does not allow H2O molecules to attack the S atom 10 S exhibits catenation properties but not Se Due to smaller size of S than Se. S-S bond is much stronger than Se-Se bond 11 S disappears when boiled with Na 2 SO 3 It forms sodium thiosulphate. Na 2 SO 3 + S Na 2 S 2 O 3 ( soluble) 12 H 2 O is liquid but H 2 S is gas O is electronegative so there is intermolecular H-bonding in water so it is liquid. 13 Ozone is powerful oxidizing agent It decomposes to form nascent oxygen 14 K a2 is less than K a1, for H 2 SO 4 in water The 2 nd proton releases from HSO - 4 which is difficult. So K a2 is less than K a1 15 O 2 is gas but sulphur is solid Due to smaller size O can form pπ-pπ multiple bond and exists as discrete diatomic molecule. 16 Group 16 elements are called chalcogens Chalcogen means ore forming elements. They form several ores 17 Positive oxidation states of O are generally not found Due to high electro negativity of O 18 Thermal stability decreases from H 2 O to H 2 Te in group 16` Due to increase in atomic size from O to Te the bond dissociation energy decreases 19 O does not show +4 & +6 oxidation states like S Due to absence of d-orbital in oxygen 20 The magnitude of electron gain enthalpy of oxygen is less than that of sulphur Due to very small size of O there is inter electronic repulsion 21 Among the hydrides of group 16 water shows unusual properties Due to H-bonding in water the molecules get associated 22 S exhibits catenation but not O Because S-S bond is stronger than O-O bond

4 23 Tendency to show -2 oxidation state diminishes from O to Po in group 16 Due to decreases in electronegetivity moving down the group 24 O 2 is paramagnetic although it has even number of electrons Due presence of unpaired electrons in anti bonding molecular orbitals 25 Sulphur in vapour state exhibit paramagnetism In vapour stare sulphur partly exists as S 2 molecule and like O 2 it has unpaired electrons in π * orbitals 26 SF 6 is less reactive than SF 4 In SF 6 sulphur atom is sterically hindered due to six F atoms GROUP-17 1 Halogens have maximum negative electron gain enthalpy( eg H) Because they have smallest size in their respective periods 2 F has less electron gain enthalpy than that of Cl but fluorine is stronger oxidizing agent than chlorine F has very small size so there is interelectronic repulsion. F is stronger oxidizing agent due to its low bond dissociation energy and high hydration energy 3 F exhibits only -1 oxidation state, other halogen shows +1, +3, +5, +7 oxidation states F is most electronegative element and due to absence of d-orbitals it can not expand its octet so it does not exhibit positive oxidation state. 4 Iron reacts with HCl gives Fe(II)chloride and not Fe(III)chloride Fe + 2 HCl FeCl 2 + H 2 H 2 liberated prevents the oxidation of FeCl 2 to FeCl 3 5 Bond dissociation energy of F 2 is less than Cl 2 Due to very small size of F there is interelectronic repulsion in F2 so it has low bond dissociation energy 6 Fluorine does not undergo disproportionation Disproportination means simultaneous oxidation-reduction. F being the most electronegative element undergoes only reduction but not oxidation. 7 NO dimerises but Cl 2 O does not NO is odd electron species so it complete its octet by dimerisation 8 Bleaching by Cl 2 is permanent but by SO 2 is temporary Cl 2 bleaches by oxidation while SO 2 does it by reduction. The reduced product gets oxidized again in air and the colour returns 9 HF has lower acid strength than HI Due to larger size of I, the H-I bond is weaker than H-F bond so HI is stronger 10 I 2 is more soluble in KI than in water I 2 forms complex with KI i.e K + I 3-11 HClO is stronger acid than HIO ClO - is more stable than IO - because Cl is more electronegative, so HClO is stronger 12 HClO 4 is stronger acid than HClO 3 ClO 4 - is more stable than ClO 3 - due to more resonance 13 OF 2 should be called fluoride of oxygen and not oxide of fluorine Because F is more electronegative than O 14 Interhalogens are more reactive than halogens They are polar 15 HF is stored in wax coated glass bottle HF reacts with alkali present in glass. 16 MF is more ionic than MCl ( M is alkali metal) Because F - is smaller than Cl - and hence it is less polarisable. 17 Cl 2 + KI brown, but excess Cl 2 turns it colourless 18 HClO 4 is stronger than H 2 SO 4

5 Because the conjugate base ClO 4 - is stable due to resonance 19 ClF 3 exists but FCl 3 does not F is smaller in size and can not accommodate three chloride ions due to steric factor. 20 HF is less volatile than HCl In HF there is intermolecular H-bonding so the HF molecules get associated 21 F form only one oxo acid, HOF Due to absence of d-orbital it can not exhibit higher oxidation states 22 O form hydrogen bonding, Cl does not O is more electronegative and small in size than Cl 23 Halogens are coloured Due to absorption of radiation from VR 24 Iodine forms I 3 - but fluorine does not form F 3 - Due to small size of fluorine 25 HI can not be prepared by heating KI with conc. H 2 SO 4 26 The magnitude of electron gain enthalpy of F is less than that of Cl Due to very small size of F there is inter electronic repulsion. 27 Fluorine is stronger oxidizing agent than chlorine though it ha lower electron gain enthalpy Fluorine has higher reduction potential value due to its low bond dissociation energy and high hydration energy with compare to chlorine. 28 Acid strength increases in the order HF< HCl < HBr < HI As size increases from F to Cl the bond dissociation energy decreases from HF to HI 29 GROUP-18 1 He, Ne do not form compound with F Due to high IE 2 Noble gases have very low b.pt Because there is only weak dispersion force between their atoms. 3 Hydrolysis of XeF 6 is not a redox reaction Because in the products formed XeOF 4 and XeO 2 F 2 the Xe has the same oxidation state (+6) as in XeF 6 4 Ne used as warning signal Because Ne light has high fog penetration power 5 Noble gases form compounds only with fluorine and oxygen Because F & O are the most electronegative elements 6 Xe does not form XeF3 or XeF5 Xe has all paired electrons so promotion of one, two or three electrons will give rise to two, four or six unpaired electrons hence can not form XeF 3 and XeF 5 7 Out of noble gases only Xe forms compounds Because Xe has comparatively low IE and vacant orbitals for promotion of electrons 8 Noble gases are mostly inert Because they have completely filled valence orbitals i.e octet configuration 9 He is used as diving apparatus Because it is less soluble in blood with compare to nitrogen 10 It is difficult to study the chemistry of Rn Because Rn is radioactive and hence very unstable 11 Noble gases have comparatively large atomic size They are mono atomic so their van der Walls radii measured which is longer than covalent/ionic or metallic radii.

PRADEEP SHARMA INSTITUTE OF COMPETITIVE STUDIES ( PICS INSTITUTE )

PRADEEP SHARMA INSTITUTE OF COMPETITIVE STUDIES ( PICS INSTITUTE ) I. Account for the following: 1. Nitrogen is not very reactive at room temperature. 2. Maximum covalency of nitrogen is 4. 3. Nitrogen does not form any pentahalide. 4. S2 formed at higher temperatures