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Notes On P-Block Elements Synopsis

Home > Study Notes > Notes On P-Block Elements Synopsis
Published in: Chemistry
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Nilesh T / Pune

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  1. p-BLOCK ELEMENTS GROUP-15 ELEMENTS GROUP-16 ELEMENTS GROUP-I? ELEMENTS GROUP-18 ELEMENTS Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240
  2. Group 15 elements Collectively, the group15 elements are called pnictogens. General electronic configuration: ns2 np 3 Elements: N P As, 51Sb, 83Bi Mc 115 Molecular formula, physical state and metallic character: N2 (unreactive gas), P 4 (solid, non-metal), AS4 and Sb4 (solid, metalloids), Bi (metal). Nitrogen exists as N2 due to its tendency to form multiple bond (Pit—P7t) and is unreactive due to high bond dissociation energy of the triple bond. Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 2
  3. Physical properties: Atomic radii increase down the group and are smaller than that of group 14 elements due to increased nuclear charge. Melting point first increases from N to As due to increase in their atomic size and decreases to Sb and Bi because of their tendency to form three covalent bonds instead of five due to inert pair effect. Ionisation enthalpy decreases regularly down the group due to increase in size and is much greater than group 14 elements due to extra stability of half-filled p-orbitals. Electronegativity decreases down the group. Allotropy: all elements except Bi show allotropy. Phosphorous has three allotropes white, red and black phosphorous. Arsenic and antimony exist in two allotropic forms i.e., yellow and grey. Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240
  4. Chemical properties: Oxidation state: Down the group, stability of +3 oxidation state increases and that of +5 decreases due to inert pair effect. Halides: General formula, EX3 or EX5 Stability: NF3 > NC13 > NBr3 (due to large difference in sizes) Lewis acid strength: PC13 > ASC13, SbC1€and PF3 > PC13 > PBr3 > P13 Lewis base strength: N13 > NBr3 > NC13 >NF3 (decreasing electron density on N as the electronegativity of halogen increases) Bond angle: PF3 < PC13 < PBr3 < P13 (decre sing bonding pair — bonding pair repulsions) Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240
  5. Hydrides: General formula, EH3 Bond angle: NH3 > PH3 > AsH3 > SbH3 > BiH3 Basic character: NH3 > PH3 (AsH3, SbH3 and BiH3 are not basic) Boiling point: PH3 < AsH3 < NH3 < SbH3 < BiH3 Melting point: PH3 < AsH3 < SbH3 < NH3 Thermal stability: NH3 > PH3 > AsH3 > SbH3 > BiH3 Reducing character: NH3 < PH3 < AsH3 < SbH < BiH3 Solubility: NH3, PH3, AsH3, SbH3, BiH3 (Soluble) Saturday, 13 February 2021 (Insoluble) PROF. NILE-SH THE-TE +919890251240
  6. Oxides: General formula, E203 and E205 Acidic strength of trioxides: N203 > P 406 > AS406 > Sb40& (electronegativity of central atom decreases) Acidic strength of oxides of nitrogen: N20 < NO < N203 < N204 < N205 (oxidation number of central atom increases) Neutral Reactivity towards metals: All these elements react with metals to form binary compound exhibiting —3 oxidation state such as ca3N2, ca3P2, Na3As2. Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240
  7. Dinitrogen (N2): Preparation: NH4C1 + NaN02—+N2t + 2H20 + NaC1 (NH4)2Cr207 + 4H20 + Cr203 + 3N2t Chemical properties: 6Li + Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240
  8. Ammonia (NH3): Preparation: Fe-M0, 750 K • AfH0 -46.1 kJ mol I -2NH N2 + 3H2 200-300 atm 2NH4C1 + + cacu + 2H20 (slaked lime) IVIg3N2 + + 2NH3 Chemical properties: NH3 + H20 cu2+ + 4NH (blue) Saturday, 13 February 2021 NH4 + OH- (deep blue) NH3 + AgC1 + (white ppt.) (colourless) PROF. NILE-SH THE-TE +919890251240
  9. Preparation and properties of oxides of nitrogen: Formula O.S. N20 NO N203 N02 N204 N205 +1 +2 +3 +4 +4 +5 Preparation NH + 21-120 2NaN02 + 2FeS04 + 3H2S04 + 2NaHS04 + 2H20 + 2NO 250 K 2NO + N 673 K + 4N02 + 02 2NO 2 4HN03 cool -N204 heat + + 2N205 PROF. NILE-SH THE-TE +919890251240 Properties Colourless gas, neutral Colourless gas, neutral Blue solid, acidic Brown gas, acidic Colourless solid/liquid, acidic Colourless solid, acidic Saturday, 13 February 2021
  10. Nitric acid (HN03): Preparation: SO + HN03 NaN03 + 5H2 Pt/Rh gauge catalyst 4NH3 + 502 4NO 6H20 500 K, 9 bar 2NO + O 3N02 + Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 Ostwald's process 10
  11. Chemical properties: Pure HN03 is colourless, however impure HN03 is yelloy in colour due to soluble oxides of nitrogen and in the gaseous state it exists as a planar molecule. It acts as a strong oxidising agent. Non-metals get converted into highest oxy-acids by hot and conc. HN03 and N02 gas is evolved . S S 04 Saturday, 13 February 2021 S n S n 03 12 —>H103 3 S b 04 PROF. NILE-SH THE-TE +919890251240 p —>H3P04 11
  12. Conc. of nitric acid Very dilute HN03 Dilute HN03 Conc. HN03 Brown ring test: HN03 reacts with metals and acts as a acid as well as oxidising agent. Fe, Zn Metal Mg, Mn Fe, zn, Sn Pb, cu, Ag, Hg Sn (t zn, Fe, Pb, cu, Ag Sn Main products H2 ± metal nitrate NH4N03 + metal nitrate NO + metal nitrate N20 + metal nitrate NH4N03 + N02 + metal nitrate N02 + H2Sn03 (meta-stannic acid) N03— + 3Fe2+ + 4 H + 3 F e 3+ + 2H20 + + H20 Saturday, 13 February 2021 (brown) PROF. NILE-SH THE-TE +919890251240 12
  13. Allotropes of phosphorous: White phosphorous: It is a white translucent waxy solid, poisonous in nature, insoluble in water, soluble in CS 2 and glows in dark (chemiluminescence). It consists of discreate tetrahedral P 4 molecule and is less stable and more reactive because of angular strain in P 4 molecule. Red phosphorous: It is odourless and having iron grey lustre, non-poisonous, insoluble in water as well as in CS2, less reactive than white phosphorous and does not glow in the dark. It is polymeric consisting of chains of 4 tetrahedra. Black phosphorous: It has two forms a-black phosphorous has opaque monoclinic or rhombohedral crystals and can be sublimed in air. ß-black phosphorous has layered structure. Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 13
  14. Phosphine (PHD: Preparation: ca3P2 + + 2PH3 PH 41 + + 1-120 + PH3 p 4 + 3 N a OH + + PH3 Properties: Colourless gas with rotten fish smell and IS highly poisonous. + 6H2 3CuS04 + + 3H2S04 (Red phosphorous) P 1--13 + Saturday, 13 February 2021 (Phosphonium bromide) PROF. NILE-SH THE-TE +919890251240 (Copper phosphide) 14
  15. Halides of phosphorous: PCL: Preparation: p 4 + + 4S02 Properties: + 2S2C12 PC13 + +3 HCI 3 H3C Saturday, 13 February 2021 pc13-...................-.....> 3 H3C-........-C + PCI 3---------->.3 —CI + H3P03 2-CI + H3P03 PROF. NILE-SH THE-TE +919890251240
  16. PC15: Preparation: P4 + + IOS02 Properties: pcls-.........................................-.>pC13 + C12 PC15 + 4 H 20 --------->H3P04 + 5HCl CH3-CH2-OH + + pocu + HCI 2Ag + + PC13 In gaseous and liquid phases, it has trigonal bipyramidal structure and in solid state, it exists as an ionic solid. in which cation is tetrahedral and anion is octahedral. Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 16
  17. Oxoacids of phosphorous: H3P04 Orthophosphoric acid OH OH H4P207 Pyrophosphoric acid Saturday, 13 February 2021 H / OH H3P03 Orthophosphorous acid H3P02 Hypophosphorous acid OH OH OH (HP03)n HO OH OH (HP03)3 Polymetaphosphoric acid PROF. NILE-SH THE-TE +919890251240 Cyclotrimetaphosphoric acid 17
  18. Group 16 elements: General electronic configuration: ns2 np 4 Elements: 80, 16S, 34Se, 52Se, 84Po, 116Lv Molecular formula, physical state and metallic character: 02 (gas), S8 (solid, non-metal), Se and Te (solid, metalloids), PO (radioactive metal) First four elements are called chalcogens which means ore forming elements. Saturday, 13 February 2021 00 PROF. NILE-SH THE-TE +919890251240 18
  19. Physical properties: Atomic and ionic radii increase down the group. Ionisation enthalpy decreases down the group and is less than that of group 15 elements due to stability of half-filled p-subshell of group 15 elements. Electronegativity decreases down the group. Electron gain enthalpy for oxygen is less negative than sulphur due to its small size. However, from sulphur onwards it again becomes less negative up to polonium. Melting point and boiling points increase down the group with increase in atomic size up to Te while PO has both melting point and boiling point less than that of Tee Oxygen is diatomic 02) due to p-p multiple bonding. Elemental state: S, Se and Te exist as octa-atomlc (S8, Sq, Teo due to absence of p-p multiple bonding. All the elements of group 16 exhibit allotropy. Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 19
  20. Chemical properties: Oxidation state: Oxygen shows oxidation states of —2, —1, —1/2, 0, +1 and +2 while other elements show oxidation state of —2, +2, +4 and +6. The stability of —2 oxidation state decreases down the group due to decrease in electronegativity and stability of +4 oxidation state increases and that of +6 oxidation state decreases down the group due to inert pair effect. Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 20
  21. Hydrides: General formula of group 16 hydrides is H2E. Physical state: 1-120 is liquid while all other hydrides are gases. Boiling point: H2S < H2Se < H2Te < H20 Volatility: H2S > H2Se > H2Te > H20 Bond angle: H20 > H2S > H2Se > H2Te Acidic character: H20 < H2S < H2Se < H2Te Reducing power: H2Te > H2Se > H2S > H20 Thermal stability: H20 > H2S > H2Se > H2Te Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 21
  22. Oxides: All group 16 elements form oxides of the type E02 and E03. Both types of oxides are acidic in nature. Reducing property decreases from S02 to Te02. Halides: Group 16 elements from halides of the typeÉX6, E 4 and EX2. Stability of the halides decreases in the order F-> IZ > Br- > I- Amongst hexa-halides SF4 is a gas, SeF4 is a liquid and TeF4 a solid. They have trigonal bipyramidal structure. All dihalides have tetrahedral structure, Mono-halides exist as dime . Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 22
  23. Dioxygen: Preparation: 2K CIO + 302 2 Ag20-------------->4Ag + 0 2pb304-..........................................>6pb0 + 02 3 Mn02 Properties: Oxygen is colourless and odourless gas, soluble in Water and paramagnetic in nature. Dioxygen directly reacts with all metals (except noble metals like Au, Pt); non-metals and some noble gases. 9 2ZnS + + 2S02 (Roasting) 2Ca + (Basic oxide) 4Al + 302 -------------->2A1203 OXIde) + 202 + 21--120 (COmbLlSti011) V205 P4 + 502 (Acidic oxide) 2S02 + 02----------------> 2S03 (Catalytic oxidation) C + 02 (Acidic oxide) cucu 4HC1 + + 2H20 (Catalytic oxidation) Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 23
  24. Oxides: Simple oxides: MgO, A1203 Mixed oxides: Pb304, Fe304 Acidic oxides: S02, C1207, CO N O Basic oxides: Na20, CaO, Bao Amphoteric oxides: A1203 Neutral oxides: CO, NO, N20 Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 24
  25. Ozone (03): Preparation: Electric discharge 302 203 Properties: It is a pale blue gas, dark blue liquid and violet black solid. 03 -...............................>02 + O (Oxidising action) 21- + H20 + 12 + 02 (Reducing action) (used for estimation of 03 bf titrating 12 with sodium thiosulphate solution) Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240
  26. Allotropes of sulphur: Rhombic sulphur (a-sulphur) has S8 molecules, yellow in colour, m.p. 385.8 K, specific gravity 2.06, insoluble in water, soluble in CS2. Monoclinic sulphur (ß-sulphur) has S8 molecules, colourless needless shaped crystals, m.p. 393 K, specific gravity 1.98, soluble in CS2. S8 ring (both in rhombic and monoclinic sulphur) is puckered and crown shaped. In cyclo S6 the ring has chair form. At elevated temperatures (—1000 K) S2 is the dominant species and is paramagnetic like 02. Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 26
  27. Sulphur dioxide (S02): Preparation: S + 02 SO SO?- + 2H + S02 (Lab preparation) 2ZnS + 302 + 2S02 (By product of roasting of sulphide ores) Physical properties: Colourless gas with pungent smell, highly soluble in water, liquifies at room temperature at 2 atm., boils at 263 K. Chemical properties: S02 + 1-120 H2S03 2NaOH + S02---------+Na2S03 + 1--120 Na2S03 + H20 + S02 + Cly..........................-..-> V205 2S02 + 02------------>2S03 Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240
  28. Bleaching action: S02 + + 2[H] Coloured matter + [H] ——————>Colourless matter Reducing nature: 2Fe3+ + S02 + 2H20 2+ 2Fe 5 S02 + 2N/ln04— + + 41-1 + 2Mn Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 28
  29. Oxoacids of sulphur: HO / HO H3S03 Sulphurous acid o / 0——0 H2S208 HO // O HO H3S04 Sulphuric acid OH HO OH Peroxodisulphuric acid Saturday, 13 February 2021 H2S207 Pyrosulphuric acid (Oleum) PROF. NILE-SH THE-TE +919890251240 29
  30. Sulphuric acid (H2S04): It is also known as oil of vitrol and king of chemicals. Preparation: It is manufactured by contact process which involves the following steps: S + 02 V205 2S02 + 02 S03 + H 2 SO 4 --—--2.----+2H2S04 (Oleum) Physical properties: H2S04 is a colourless, dense, oily liquid with specific gravity of 1.8 at 298 K. Dissolution of sulphuric acid in water is highly exothermic hence conc. acid must be added into water with constant stirring. Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 30
  31. Chemical properties: H2S04 + H 20 -.........................................>H30 HS04- + H Strong dibasic acid + SO 42 NaOH + H 2 SO + 1-120 (Acid sulphate) 2NaOH + + 2H20 (Normal sulphate) 2MX + + M2S04 (X = F, Cl, N03) (less volatile —(more volatile (M = Metal) acid) Saturday, 13 February 2021 acid) H2S04 + I IH20 (Strong dehydrating agent) PROF. NILE-SH THE-TE +919890251240 31
  32. Cu + + S02 (Conc.) S + 2 + 21--120 (Conc.) C + 2 H 2 so 4---------->C02 + 2H20 2H20 (Conc.) Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 32
  33. Group 17 elements: General electronic configuration: ns2 np 5 Elements: F Cl, 1 At Ts 9 17 53 85 117 Molecular formula and physical state: F2 (pale yellow gas), C12 (greenish yellow gas), Br2 (reddish brown liquid), 12 (purple solid . Occurrence: Not found in free state as theycare very reactive. Found as halides, X . Fluorine is found in the form of fluorite, fluorspar, cryolite. Chlorine is the most abundant in the form of NaCl in oceans, salt lakes, rock beds. Bromides are found in sea water and salt lakes. Iodine is found in sea weeds as I- and 103 in Chile salt petre. Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 33
  34. Physical properties: Atomic and ionic radii: Increase down the group and halogens are smallest atoms in a period. Ionisation enthalpy is very high and decreases down the group. Electronegativity: Fluorine is the most electronegative element and electronegativity decreases down the group. Electron gain enthalpy increases from F to Cl and then decreases to I. Smaller electron gain enthalpy of F is due to small size and inter electronic repulsions. Bond dissociation enthalpy increases from F2 to C12 and then decreases in Br2 and 12. F—F bond is weaker than CI—CI because of the large repulsions of the lone pairs of F2 which are closer than in C12. Melting points and boiling points increase down the group. Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 34
  35. Chemical properties: Oxidation states: F shows only —1 oxidation state as it is the most electronegative element. Other elements show —1, +1, +3, +5 and +7 oxidation states. Higher oxidation states of Cl, Br and I are observed only in fluorides, oxides and oxoacids. Oxidising power: F2 > C12 > > 12 20 Reduction potentials decrease from 2 to 12 A halogen of lower atomic number oxidlses a halide ion of higher atomic number. Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 35
  36. Hydrogen halides: The order of reactivity: F2 > C12 > Br2 > 12 Boiling points: HF > HI > HBr > HCI Melting points: HI > HF > HBr > HCI Oxides: HCI HBr 50 Fluorine forms two oxides OF2 and 02F2 called oxygen fluorides, other halogens form oxides in which oxidation states of hese halogens range from +1 to +7. The higher oxides of halogens are more stable than the lower ones. Metal halides: Ionic character: MF > MCI > MBr > Ml For metals exhibiting more than one oxidation states, the halides in higher oxidation states will be more covalent than the one in lower oxidation states. Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 36
  37. Chlorine (C12): Discovered by Scheele in 1774. Preparation: Mn02 + + 2H20 + C12 4NaC1 + Mn02 + 4NaHS04 + 2H20 + C12 2KMn04 + 16HCl—--+2KCl + 2MnC12 + 8H20 + 5C12 cucu 4HCl + + 2H20 [Deacon's process for manufacture of C121 Physical properties: Greenish yellow gas with pungent and suffocating odour, heavier than air, liquifies easily, soluble in water. Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 37
  38. Chemical properties of C12: It reacts with metal and non-metals to form chlorides. It reacts with compounds containing hydrogen to form HCI. H2S + + S Reaction with ammonia: 8NH3 + + N2 (excess) Reaction with alkalis: C H + 6 HCI + 10 16 H3 + + 3HCl (excess) 2NaOH + + NaOC1 + H20 (cold & dilute) -------—>5NaCl + NaC103 + 31-120 2NaOH + 3C12 (hot & conc.) Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 38
  39. Reaction with slaked lime: + + CaC12 + 2H20 Oxidising agent: 2FeS04 + H2S04 + + 2HC1 S02 + 2H20 + 2HCl 12 + 6H20 + + IOHCI Bleaching agent: C12 + H 20---------> 2HC1 + [O] Coloured substance + [O] ----——>Colourless substance Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 39
  40. Hydrogen chloride (HCI): Lab preparation: 420 K NaC1 + + HCI 823 K NaHS04 + NaCl--------------------------->Na2S04 + Physical properties: Colourless pungent smelling gas, easily liquified, extremely soluble in water. Chemical properties: It decompokeé salte of weaker acids. Na2C03 + + H20 + C02 Na2S03 + + H20 + S02 Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 40
  41. Aqua regia (3 parts of conc. HCI and 1 part of conc. HN03) is used for dissolving noble metals. e.g., gold, platinum. A u + 4H + N 03 — + + NO + 21-120 3 pt + 16 H + 4N03— + 1 + 4 NO + 81-120 Oxoacids of halogens: Fluorine forms only one oxoacid (HOF), while al other halogens form oxoacids of the type HOX, HX02, HX03 and HX04 Acid strength: HC104 > HC103 > HC102 > HCIO and HOCI > HOBr > HOI Oxidising power: HOCI z HOBr > HOI and Broc > 104- > C104 Interhalogens compounds: Halogens combine amongst themselves to form a number of interhalogens of the type XX', XX'3, XX'5 and XX'7, where X is a larger size halogen (more electropositive) and X' is smaller size halogen. Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 41
  42. Group 18 elements: They are also called noble gases. General electronic configuration: ns2 np 6 Elements: 2He, IONe, 18Ar, 36Kr, 54Xe, 86Rn, Molecular formula and physical state: All are monoatomic gases. Physical properties: Ionisation enthalpy is very high and'ecyeases down the group with increase in size. Atomic radii increase down the group. Electron gain enthalpy is positive as noble gases have no tendency to accept the electron. Melting points and boiling points are very low due to weak interatomic dispersion forces. Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 42
  43. Chemical properties: Noble gases are least reactive due to high ionisation enthalpy and more positive electron gain enthalpy. Xenon-fluorine compounds: 673K 1 bar Xe + F 2 (excess) Saturday, 13 February 2021 873K 7 bar Xe + 2F2 (1: 5 ratio) 573 K, 60-70 bar Xe + 3F2 xeF6 (1: 20 ratio) PROF. NILE-SH THE-TE +919890251240 43
  44. Xenon-oxygen compounds: 6XeF4 + + 2Xe03 + 24HF + 302 XeF6 + 3 H 20--------->Xe03 + 6HF xeF6 + H20 —-—XeOF4 + 2HF Partial hydrolysis of XeF6 xeF6 + 4HF Saturday, 13 February 2021 PROF. NILE-SH THE-TE +919890251240 44
  45. Structures of compounds of xenon: xeF2 Linear sp3d Saturday, 13 February 2021 xeF4 Square planar sp3d2 xeF6 Distorted octahedral sp3d3 PROF. NILE-SH THE-TE +919890251240 xe03 Pyramidal sp 45

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