The d -Block Elements

Transcription

1 The d-block Elements

2 Introduction d-block elements locate between the s-block and p-block known as transition elements occur in the fourth and subsequent periods of the Periodic Table 2

3 d-block elements period 4 period 5 period 6 period 7 3

4 Introduction Transition elements are elements that contain an incomplete d sub-shell (i.e. d 1 to d 9 ) in at least one of the oxidation states of their compounds. 3d 0 3d 10 4

5 Introduction Sc and Zn are not transition elements because They form compounds with only one oxidation state in which the d sub-shell are NOT imcomplete. Sc Sc 3+ 3d 0 Zn Zn 2+ 3d 10 5

6 Introduction Cu + 3d 10 not transitional Cu Cu 2+ 3d 9 transitional 6

7 The first transition series the first horizontal row of the d-block elements 7

8 Characteristics of transition elements (d-block metals vs s-block metals) 1. Physical properties vary slightly with atomic number across the series (cf. s-block and p-block elements) 2. Higher m.p./b.p./density/hardness than s-block elements of the same periods. 3. Variable oxidation states (cf. fixed oxidation states of s-block metals) 8

9 Characteristics of transition elements 4. Formation of coloured compounds/ions (cf. colourless ions of s-block elements) 5. Formation of complexes 6. Catalytic properties 9

10 Electronic Configurations Valence electrons in the inner 3d orbitals Examples: The electronic configuration of scandium: 1s 2 2s 2 2p 6 3s 2 3p 6 3d 1 4s 2 The electronic configuration of zinc: 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 10

11 Electronic configurations of the first series of the d-block elements Element Atomic number Electronic configuration 11 Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc [Ar] 3d 1 4s 2 [Ar] 3d 2 4s 2 [Ar] 3d 3 4s 2 [Ar] 3d 5 4s 1 [Ar] 3d 5 4s 2 [Ar] 3d 6 4s 2 [Ar] 3d 7 4s 2 [Ar] 3d 8 4s 2 [Ar] 3d 10 4s 1 [Ar] 3d 10 4s 2

12 A half-filled or fully-filled d sub-shell has extra stability 12

13 d -Block Elements as Metals d-block elements are typical metals Physical properties of d-block elements : good conductors of heat and electricity hard and strong malleable and ductile 13

14 d -Block Elements as Metals Physical properties of d-block elements: lustrous high melting points and boiling points Exceptions : Mercury low melting point liquid at room temperature and pressure 14

15 d -Block Elements as Metals d-block elements extremely useful as construction materials strong and unreactive 15

16 Scandium chemistry strongly resembles lanthanides Titanium excellent structural material (light weight) Vanadium mostly in alloys with other metals Chromium important industrial material Manganese production of hard steel Iron most abundant heavy metal Cobalt alloys with other metals Nickel plating more active metals; alloys Copper plumbing and electrical applications Zinc galvanizing steel 16

17 Atomic Radii and Ionic Radii Two features can be observed: 1. The d-block elements have smaller atomic radii than the s-block elements 2. The atomic radii of the d-block elements do not show much variation across the series 17

18 Atomic Radii and Ionic Radii atomic number effective nuclear charge the electron clouds are pulled closer to the nucleus atomic size 18

19 Many of the differences in physical and chemical properties between the d-block and s-block elements explained in terms of their differences in electronic configurations and atomic radii 19

20 1. Density Densities (in g cm 3 ) of the s-block elements and the first series of the d-block elements at 20 C 20

21 1. Density d-block > s-block the atoms of the d-block elements 1. are generally smaller in size 2. are more closely packed 3. have higher relative atomic masses 21

22 2. Ionization Energy The first ionization energy of the d-block elements greater than those of the s-block elements in the same period of the Periodic Table 1. The atoms of the d-block elements are smaller in size 2. greater effective nuclear charges 22

23 3. Melting Points and Hardness d-block >> s-block 1. both 4s and 3d e - are involved in the formation of metal bonds 2. d-block atoms are smaller

24 3. Melting Points and Hardness The hardness of a metal depends on the strength of the metallic bonds The metallic bonds of the d-block elements are stronger than those of the s-block elements much harder than the s-block elements 24

25 Mohs scale : - A measure of hardness Talc Diamond 0 10 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn

26 4. Reaction with Water In general, the s-block elements react vigorously with water to form metal hydroxides and hydrogen The d-block elements react very slowly with cold water react with steam to give metal oxides and hydrogen 26

27 4. Reaction with Water 2K(s) + 2H 2 O(l) 2Na(s) + 2H 2 O(l) Ca(s) + 2H 2 O(l) Zn(s) + H 2 O(g) 3Fe(s) + 4H 2 O(g) 2KOH(aq) + H 2 (g) 2NaOH(aq) + H 2 (g) Ca(OH) 2 (aq) + H 2 (g) ZnO(s) + H 2 (g) Fe 3 O 4 (s) + 4H 2 (g) 27

28 d-block compounds vs s-block compounds A Summary : - 28 Ions of d-block metals have higher charge density more polarizing 1. more covalent in nature 2. less soluble in water 3. less basic (more acidic) Basicity : Fe(OH) 3 < Fe(OH) 2 << NaOH Charge density : Fe 3+ > Fe 2+ > Na +

29 d-block compounds vs s-block compounds A Summary : - 4. less thermally stable e.g. CuCO 3 << Na 2 CO 3 5. tend to exist as hydrated salts e.g. CuSO 4.5H 2 O, CoCl 2.2H 2 O 6. hydrated ions undergo hydrolysis more easily e.g. [Fe(H 2 O) 6 ] 3+ (aq) + H 2 O [Fe(OH)(H 2 O) 5 ] 2+ (aq) + H 3 O + acidic 29

30 Variable Oxidation States One of the most striking properties variable oxidation states The 3d and 4s electrons are in similar energy levels available for bonding 30

31 Variable Oxidation States Elements of the first transition series form ions of roughly the same stability by losing different numbers of the 3d and 4s electrons 31

32 Oxidation states of the elements of the first transition series in their compounds 32 Element Sc Ti V Cr Mn Fe Co Ni Cu Zn Possible oxidation state

33 1. Scandium and zinc do not exhibit variable oxidation states Scandium of the oxidation state +3 the stable electronic configuration of argon (i.e. 1s 2 2s 2 2p 6 3s 2 3p 6 ) Zinc of the oxidation state +2 the stable electronic configuration of [Ar] 3d 10 33

34 3. Manganese has the highest oxidation state +7 E.g. MnO 4-, Mn 2 O 7 Mn 7+ ions do not exist. 34

35 Formation of Complexes Another striking feature of the d-block elements is the formation of complexes 35

36 Formation of Complexes A complex is formed when a central metal atom or ion is surrounded by other molecules or ions which form dative covalent bonds with the central metal atom or ion. The molecules or ions that donate lone pairs of electrons to form the dative covalent bonds are called ligands. 36

37 Formation of Complexes A ligand can be an ion or a molecule having at least one lone pair of electrons that can be donated to the central metal atom or ion to form a dative covalent bond 37

38 Formation of Complexes Complexes can be electrically neutral Ni(CO) 4 positively charged negatively charged [Co(H 2 O) 6 ] 3+ [Fe(CN) 6 ] 3 38

39 A co-ordination compound is either a neutral complex e.g. Ni(CO) 4 or made of a complex ion and another ion e.g. [Co(H 2 O) 6 ]Cl 3 [Co(H 2 O) 6 ] Cl K 3 [Fe(CN) 6 ] 3K + + [Fe(CN) 6 ] 3 39

40 Criteria for complex formation 1. Presence of vacant and low-energy 3d, 4s, 4p and 4d orbitals in the metal atoms or ions to accept lone pairs from ligands. 2. High charge density of the central metal ions. 40

41 [Co(H 2 O) 6 ] 2+ Co : 3d 4s 4p 4d Co 2+ : 3d 4s 4p 4d The six sp 3 d 2 orbitals accept six lone pairs from six H 2 O. sp 3 d 2 hybridisation Arranged octahedrally to minimize repulsion between dative bonds. 41

42 The transition metal ion accepts lone pairs of electrons from the ligands in forming dative covalent bonds. The ligand donates a lone pair of electrons to the transition metal ion in forming dative covalent bonds. 42

43 1. Complexes with Monodentate Ligands A ligand that forms one dative covalent bond only is called a monodentate ligand. Examples: neutral CO, H 2 O, NH 3 anionic Cl, CN, OH 43

44 44

45 Coloured Ions 45 The colours of many gemstones are due to the presence of small quantities of d-block metal ions

46 Coloured Ions Most of the d-block metals form coloured compounds due to the presence of the incompletely filled d orbitals in the d-block metal ions Which aqueous transition metal ion(s) is/are not coloured? 46 3d 10 : Zn 2+, Cu + ; 3d 0 : Sc 3+, Ti 4+

47 Co 2+ (aq) Zn 2+ (aq) Fe 3+ (aq) Colours of some d-block metal ions in aqueous solutions 47

48 Mn 2+ (aq) Fe 2+ (aq) Cu 2+ (aq) Colours of some d-block metal ions in aqueous solutions 48

49 A substance absorbs visible light of a certain wavelength reflects or transmits visible light of other wavelengths (complimentary colour) appears coloured Coloured ion Light absorbed Light reflected or transmitted [Cu(H 2 O) 4 ] 2+ (aq) Yellow Blue [CuCl 4 ] 2 (aq) Blue Yellow 49

50 Complimentary colour chart Blue light absorbed Appears yellow Blue Violet Magenta Cyan Red Yellow light absorbed Appears blue Green Yellow Greenish yellow 50

51 Coloured Ions The absorption of visible light is due to the d-d electronic transition 3d 3d i.e. an electron jumping from a lower 3d orbital to a higher 3d orbital 51

52 Catalytic Properties of Transition Metals and their Compounds The d-block metals and their compounds important catalysts in industry and biological systems 52

53 Catalytic Properties of Transition Metals and their Compounds The d-block metals and their compounds exert their catalytic actions in either heterogeneous catalysis homogeneous catalysis 53