Properties of II B Group Elements

Size: px

Start display at page:

Download "Properties of II B Group Elements"

Reynold Thompson
5 years ago
Views:

1 Properties of II B Group Elements

2 d-block Transition Elements VIIIB IIIB IVB VB VIB VIIB IB IIB Sc Ti V Cr Mn Fe Co Ni Cu Zn Y Zr Nb Mo Tc Ru Rh Pd Ag Cd La Hf Ta W Re Os Ir Pt Au Hg

3 II B Group Elements Element Zn Cd Hg z A r 65,4 112,4 200,59 1,66 1,46 1,44

4 II B Group Elements General electron configuration: [ ] ns 2 (n 1)d 10 np 0 nd 0 ns 2 (n 1)d 10 Oxidation states: +II, +I (Hg) Their characteristic is that either the neutral atom or one of its ions has complete set of d electrons.

5 The elements Zn and Cd have unique properties. They resemble alkaline earth metals No Oxidation state higher then +2 Zinc and cadmium are white, tarnishable metals Hg is a shiny liquid at ordinary temperature.

6 Simple compounds Zinc Cadmium Mercury melting pt, С 419,5 321,1 38,9 boiling pt, С 906,2 766,5 356,7 density, g/cm 3 7,14 8,65 13,53 Zinc Mercury Cadmium

7 As can be seen from the table before, Hg has very special properties as compared with the other elements. Hg can not be considered as a homologue to Zn and Cd.

8 Occurrence in earth crust and ores Low occurrence in earth crust 25. Zn 0,012 % 63. Hg % 64. Cd % Cinnabar HgS Greenockite CdS Sphalerite ZnS Smithsonite ZnCO 3 Corderoite Hg 3 S 2 Cl 2

9 Zinc and cadmium have been known long time, easily prepared from ores. Zinc occurs widely, Cd occurs rare, but is found in Zn ores. Flotation Roasting Methods of isolation involve Metal oxide ZnO can be reduced with carbon to the metal. ZnO + C =Zn + CO Cadmium is invariably a by-product and is usually separated from Zn by distillation. Or by precipitation from sulfate solutions by Zn dust. Zn + CdSO 4 = ZnSO 4 + Cd

10 The only mercury ore is cinnabar HgS. It is roasted to give the oxide The Oxide is thermically decomposed at 500 C and Hg vaporizes. t 2HgO = 2Hg + O 2

11 Zinc and cadmium

12 Activity increse Zn Cd Hg... Hg... H.. Cd.. Zn.. Amphoteric Zn + 2 HCl = ZnCl 2 + H 2 Cd + 2 HCl = CdCl 2 + H 2 Hg + HCl no reaction Metal Both Zn and Cd react readily with non oxidizing acids releasing H 2 and giving the divalent ions; Hg is inert to non oxidizing acids ; Zn also dissolves in strong bases under formation of zi ncate ions: Zn + 2 NaOH+ 2H 2 O = Na 2 [Zn(OH) 4 ] + H 2 Cd + 2 NaOH (dilute)

13 All three elements react with halogens and with nonmetals such as S, Se, and P. The elements Zn and Cd form many alloys. E.g. brass, which is a copper zinc alloy, which is of technical import ance. Mercury combines with many other metals, sometimes with difficulty but sometimes, as with Na or K, very vigorously, giving amalgams.

14 Reducing properties of Zn Zn + KNO 3 + H 2 SO 4 = ZnSO 4 + KNO 2 + H 2 O Zn 0 2e = Zn 2+ N e = N 3+

Peculiarities of mercury Hg(l) can vaporize, poison

of mercuric salts owing to reduction by traces of

15 Peculiarities of mercury Hg(l) can vaporize, poison CH 3 Hg + the most strong poison Hg forms amalgams (example Na x Hg y ) 2NaHg + 2H 2 O = 2Hg + 2NaOH + H 2 Mercury is readily lost from aqueous solutions of mercuric salts owing to reduction by traces of redu cing materials and by disproportionation of Hg 2 +2

16 Hg + HNO 3 Hg + 4HNO 3 (conc.) = Hg(NO 3 ) 2 + 2NO 2 + 2H 2 O; 6Hg + 8HNO 3 (dilut.) = 3Hg 2 (NO 3 ) 2 + 2NO + 4H 2 O; Hg 2 +I (NO 3 ) 2 + 4HNO 3 (conc) = 2Hg+II (NO 3 ) 2 + 2NO 2 + 2H 2 O

17 Compounds in oxidation state +1 The univalent state Zn, Cd, and Hg form the ions M M 2 +2 = ( + M M + ) Zn 2 +2 and Cd 2 +2 ions are unstable Found only in melts or solids. If one adds Zn to fused ZnCl 2, this gives a yellow solution. Upon cooling it gives a yellow glass, containing Zn 2 +2 The ions have a metal metal bond ( + M M + ); the order of bo nd strength is : Zn 2 +2 < Cd 2 +2 < Hg 2 +2.

18 The mercury(i) ion (Hg 2 +2 ) is formed on reduction of Hg(II) salts in aqueous solution Hg 2 2+ Hg 0 + Hg 2+ Dimercury (I) Compounds no hydroxide, oxide, or sulfide can be obtained by addition of the appropriate anion to aqueous Hg 2 2+ best known dimercury (I) compounds are the halides Ex. Hg 2 Cl 2 mercury (I) chloride (calomel) fluoride is unstable toward water hydrolyzes to hydroflu oric acid and hydroxide which immediately disproportionates

19 Hg 2 2+ Hg OH = HgO + Hg + H 2 O Hg H 2 S = HgS + Hg + 2H +

20 Compounds in oxidation state +2 OXIDES ZnO CdO HgO The oxides (ZnO and CdO) are formed on burning the metals in air or by pyrolysis of the carbonates or nitrates. 2Zn + O 2 = 2ZnO CdCO 3 = CdO + CO 2 The cadmium oxide smokes are exceedingly toxic. Zinc oxide is normally white but turns yellow on heating. Cadmium oxide varies in color from greenish yellow through brown to nearly black.

21 Both Zn and Cd react readily when heated in O 2, to give the oxides. Although Hg and O 2 are unstable with respect to HgO at 25 0 C reaction rate is veeeeeryslow. Hg + O 2 = 2HgO the reaction proceeds at a useful rate at C, but above ab out C HgO decomposes rapidly into the elements. HgO = Hg + ½ O 2

22 ZnO CdO HgO Thermal stability decreases ZnO CdO t t 2HgO 2Hg + O 2 ( С)

23 ZnO, CdO and HgO do not react with water but dissolve in acids and bases ZnО + 2HCl = ZnCl 2 + 2H 2 O ZnО + 2NaOH = Na 2 ZnО 2 + H 2 O

24 Zn(OH) 2 Cd(OH) 2 Hg(OH) 2 does not exist Amphoteric The hydroxides are precipitated from solutions of salts by addition of bases. ZnCl 2 + 2NaOH = Zn(OH) 2 + 2NaCl The compound Zn (OH) 2 readily dissolves in an excess of alkali bases to give "zinca te. Zn(ОH) 2 + 2NaOH = Na 2 [Zn(ОH) 4 ] Cadmium hydroxide, Cd(OH) 2, is soluble only in concentrated bases.

25 Both Zn and Cd hydroxide readily dissolve in an excess of strong ammonia to form the amine complexes. Zn(ОH) 2 + 4NH 3 = [Zn(NH 3 ) 4 ](OH) 2 Cd(ОH) 2 + 4NH 3 = [Cd(NH 3 ) 4 ](OH) 2 Sulfides. The sulfides are obtained by direct interaction o r by precipitation by H 2 S from aqueous solutions Acidic s olution for CdS and neutral or basic solution for ZnS. ZnCl 2 + H 2 S = ZnS+ 2HCl Zn + S = ZnS

26 HgCl 2 HgCl 2 + 2NaOH = HgO + H 2 O + NaCl Hg Cl 2 + H 2 S = HgS + 2HCl

27 Oxidation redaction properties Hg(NO 3 ) 2 + 2HCl = HgCl 2(р) + 2H 2 O 2HgCl 2 + [SnCl 3 ] + Cl = Hg 2 Cl 2(т) + [SnCl 6 ] 2 Hg 2 Cl 2 + [SnCl 3 ] + Cl = 2Hg + [SnCl 6 ] 2

28 Application Zinc dithiocarbamates are industrially important as accelerators in the vulcanization of rubber by sulfur. Zinc complexes are also of great importance biologically Zinc compounds, especially ZnCO 3 and ZnO, are used in ointments, since zinc apparently promotes healing processes. Cadmium compounds are extremely poisonous, possibly because of the substitution of Cd for Zn in an enzyme system, and consequently they constitute a serious environmental hazard (e.g., in the neighbo rhood of Zn smelters).

E3 Redox: Transferring electrons. Session one of two First hour: Discussion (E1) 2nd and 3rd hour: Lab (E3, Parts 1 and 2A)

E3 Redox: Transferring electrons Session one of two First hour: Discussion (E) 2nd and 3rd hour: Lab (E3, Parts and 2A) Oxidation-Reduction (Redox) Reactions involve electron transfer. Change in charge