D-block Elements - Inorganic Chemistry Notes

Notes for d-block elements: Inorganic Chemistry

1. d-BLOCK ELEMENTS

2. https://pubchem.ncbi.nlm.nih.gov/periodic-table/#view=table

3. Introduction d-block elements are also called transition elements All the d-block elements are not transition metals Groups 3 – 12 ----- d-block elements According to IUPAC, transition metals are defined as metals which have incomplete d sub-shell either in neutral atom or in their ions. Zinc, cadmium and mercury of group 12 have full d 10 configuration in their ground state as well as in their common oxidation states and hence, are not regarded as transition metals Lanthanum (La) and actinium (Ac) are elements that belong to the f-block of the periodic table. However, they are commonly placed in the d-block due to a historical convention based on their electron configurations The filling of electrons follows Aufbau principle. However, introduction of d and f  orbitals and resulting poor shielding affects predicted energy order, and it consists last 2 or three shells incompletely filled. The energy associated with this subshells is nearly same, and one of the subshell of outer shell is bigger in size than subshell of inner shell. So, to perform minimum repulsion between electrons, one or two electrons jump to a bigger subshell (with similar energy) so this exceptions occur. In case of cerium, energy of 4f and 5d  subshells are quite similar and 5d  subshell is bigger than 4f subshell . So 1 electron in 4f jump to 5d subshell. https://oercommons.org/courseware/lesson/71985/overview https://edurev.in/question/512198/Though-lanthanum-and-actinium-are-f-block-elements https://chemistry.stackexchange.com/questions/112478/two-different-electronic-configurations-for-cerium

4. Electronic Configuration of Transition Elements The valence shell electronic configuration of d-block elements or transition metals, (n−1)d 1 to 10  ns 1,2 The electronic configuration for period 4, transition elements is ( Ar ) 4s  1-2  3d  1-10 The electronic configuration for period 5, transition elements is (Kr) 5s  1-2  4d  1-10 The electronic configuration for period 6, transition elements is ( Xe ) 4s  1-2  3d  1-10

5. Electronic configuration of the first transition series Transition element Symbol Atomic number Electronic configuration Scandium Sc 21 [ Ar ] 3d 1  4s 2 Titanium Ti 22 [ Ar ] 3d 2  4s 2 Vanadium V 23 [ Ar ] 3d 3  4s 2 Chromium Cr 24 [ Ar ] 3d 5  4s 1 Manganese Mn 25 [ Ar ] 3d 5  4s 2 Iron Fe 26 [ Ar ] 3d 6  4s 2 Cobalt Co 27 [ Ar ] 3d 7  4s 2 Nickel Ni 28 [ Ar ] 3d 8  4s 2 Copper Cu 29 [ Ar ] 3d 10  4s 1 Zinc Zn 30 [ Ar ] 3d 10  4s 2 Electronic configuration of second transition series Transition element Symbol Atomic number Electronic configuration Yttrium Y 39 [Kr] 4d 1  5s 2 Zirconium Zr 40 [Kr] 4d 2  5s 2 Niobium Nb 41 [Kr] 4d 4  5s 1 Molybdenum Mo 42 [Kr] 4d 5  5s 1 Technetium Tc 43 [Kr] 4d 5  5s 2 Ruthenium Ru 44 [Kr] 4d 7  5s 1 Rhodium Rh 45 [Kr] 4d 7  4s 2 Palladium Pd 46 [Kr] 4d 10  5s Silver Ag 47 [Kr] 4d 10  5s 1 Cadmium Cd 48 [Kr] 4d 10  5s 2 https://www.priyamstudycentre.com/2021/03/transition-metals.html

6. Electronic configuration of the third transition series Transition element Symbol Atomic number Electronic configuration Lanthanum La 57 [Xe] 4f  5d 1  6s 2 Hafnium Hf 72 [ Xe ] 4f 14  5d 2  6s 2 Tantalum Ta 73 [ Xe ] 4f 14  5d 3  6s 2 Tungsten W 74 [ Xe ] 4f 14  5d 4  6s 2 Rhenium Re 75 [Xe] 4f 14  5d 5  6s 2 Osmium Os 76 [Xe] 4f 14  5d 6  6s 2 Iridium Ir 77 [Xe] 4f 14  5d 7  6s 2 Platinum Pt 78 [ Xe ] 4f 14  5d 9  6s 1 Gold Au 79 [ Xe ] 4f 14  5d 10  6s 1 Mercury Hg 80 [ Xe ] 4f 14  5d 10  6s 2 Electronic configuration of the fourth transition series Transition element Symbol Atomic number Electronic configuration Actinium Ac 89 [ Rn ] 5f  6d 1  7s 2 Rutherfordium Rf 104 [ Rn ] 5f 14  6d 2  7s 2 Dubnium Db 105 [ Rn ] 5f 14  6d 3  7s 2 Seaborgium Sg 106 [ Rn ] 5f 14  6d 4  7s 2 Bohrium Bh 107 [ Rn ] 5f 14  6d 5  7s 2 Hassium Hs 108 [ Rn ] 5f 14  6d 6  7s 2 Meitnerium Mt 109 [ Rn ] 5f 14  6d 7  7s 2 Darmstadtium Ds 110 [ Rn ] 5f 14  6d 8  7s 2 Roentgenium Rg 111 [ Rn ] 5f 14  6d 9  7s 2 Copernicium Cn 112 [ Rn ] 5f 14  6d 10  7s 2 https://www.priyamstudycentre.com/2021/03/transition-metals.html

7. Valence configuration of d-block elements - (n-1)d 1– 10 ns 1–2 Exceptions Palladium(Pd)- 4d 10 5s – Because of little energy difference between 4d and 5s Half and completely filled orbitals – Relatively more stable Example: Chromium(Cr) - 3d 5 4s 1 instead of 3d 4 4s 2 and Copper(Cu) - 3d 10 4s 1 instead of 3d 9 4s 2 because the energy gap between the two set of orbitals is small The electronic configurations of outer orbitals of Zn, Cd , Hg and Cn are represented by the general formula (n-1)d 10 ns 2 . The orbitals in these elements are completely filled in the ground state as well as in their common oxidation states. Therefore, they are not regarded as transition elements. The number of electrons in the outermost shell is invariably 0, 1, or 2. With partly filled d orbitals these elements exhibit certain characteristic properties such as display of a variety of oxidation states, formation of coloured ions and entering into complex formation with a variety of ligands . The transition metals and their compounds also exhibit catalytic property and paramagnetic behaviour .

8. Metallic Character of Transition Elements All the transition elements are metals due to their small number of electrons or free electrons in the outermost quantum shell. Metallic character of an element can be defined as the tendency of an element to form a cation by the lose of one or more electrons In general, all the transition elements have low ionization energy Exhibit as solids at room temperature except mercury Displays typical metallic properties such as high tensile strength, ductility, malleability, high thermal and electrical conductivity and metallic lustre . Exists as hexagonal closed packed, body-centered cubic and cubic close packed lattice structures Exceptions of Zn, Cd, Hg and Mn , d-block elements have one or more typical metallic structures at normal temperatures. Hg crystal structure – Rhombohedral

9. Metallic character decreases from left to right Reason : Nuclear charge increases because of increase in number of protons. Hence nuclear force of attraction also increases. Therefore removal of electrons from the outermost shell to form a cation will become difficult. Metallic character increases down the group Reason : Atomic radius increases because of increase in the no. of shell by one. Hence removal of electron becomes easier.

10. Except Zn, Cd, Hg and Mn , rest of the elements show one or more metallic characters at normal temperatures as they have low ionization energies and have several vacant orbitals in their outermost shell This property favors the formation of metallic bonds in the transition metals and so they exhibit typical metallic properties These metals are hard which indicates the presence of covalent bonds. This happens because transition metals have unpaired d-electrons. The d-orbital which contains the unpaired electrons may overlap and form covalent bonds Higher the number of unpaired electrons present in the transition metals, more is the number of covalent bonds formed by them. This further increases the hardness of the metal and its strength e.g. chromium (Cr), tungsten (W) and molybdenum (Mo) are very hard The transition elements are very hard and possess metallic character; this indicates that both metallic and covalent bonding exists together in these elements. On the other hand zinc (Zn), cadmium ( Cd ) and mercury(Hg) which are not very hard as they do not possess unpaired d-electrons. Metallic bond – attraction of metal cations/atoms and delocalized electrons Strength of metallic bond depends on the presence of unpaired electrons https://www.flexiprep.com/Important-Topics/Chemistry/Difference-Between-Ionic-Covalent-and-Metallic-bonds.html

11. Melting and Boiling Point In general melting point of d-block > s-block elements Reason : Stronger metallic bond and presence of covalent bond formed by unpaired d-electrons High melting point represents the strength of metallic bond of an element which has more number of unpaired electrons The high melting points of these metals are attributed to the involvement of greater number of electrons from (n-1) d in addition to the n s electrons in the interatomic metallic bonding.

12. Consider 3d series, melting point increases from Sc to Cr due to the presence of increase in the number of unpaired electrons, thereby increase in the interatomic metallic bonding as well as high enthalpy of atomization values. Mn (& Tc in 4d series) have comparatively low melting point, due to weak metallic bond because of stable half filled (d 5 ) configuration. Hence does not involve in interatomic metallic bonding Melting point of Fe again increased from Mn because of more number of unpaired electrons Melting point decreases from Fe to Zn due to the decrease in the number of unpaired electrons Same reason can be applicable for the melting point trend of 4d series In Zn, Cd, and Hg there is no unpaired electron present in d-orbital, hence due to absence of covalent bond melting and boiling point are very low in series. (Volatile metals Zn, Cd, Hg) Melting point increases from 3d to 5d series because of increase in enthalpy of atomization as well as increase in metallic character down the group in the periodic table Electronic configuration of the 3d-transition series Element Symbol At. No. Electronic configuration Scandium Sc 21 [ Ar ] 3d 1  4s 2 Titanium Ti 22 [ Ar ] 3d 2  4s 2 Vanadium V 23 [ Ar ] 3d 3  4s 2 Chromium Cr 24 [ Ar ] 3d 5  4s 1 Manganese Mn 25 [ Ar ] 3d 5  4s 2 Iron Fe 26 [ Ar ] 3d 6  4s 2 Cobalt Co 27 [ Ar ] 3d 7  4s 2 Nickel Ni 28 [ Ar ] 3d 8  4s 2 Copper Cu 29 [ Ar ] 3d 10  4s 1 Zinc Zn 30 [ Ar ] 3d 10  4s 2 Lowest melting point Hg (– 38.8°C) Highest melting point W ( ~ 3400°C) The enthalpy of atomization is defined as enthalpy change occurring in the separation of all the atoms from a lattice of metal. 

13. Variation in atomic size In general, atomic size decreases from left to right because of increase in nuclear charge because of electrons added in the same shell thereby increase in the nuclear force of attraction between the nucleus and the outermost shell Atomic size increases down the group because of electrons added in the next shell thereby decrease in the nuclear force of attraction between the nucleus and the outermost shell

14. Atomic radius (in pm) of transition elements 3 4 5 6 7 8 9 10 11 12 Sc 162 Ti 147 V 134 Cr 127 Mn 126 Fe 126 Co 125 Ni 124 Cu 128 Zn 137 Y 180 Zr 160 Nb 146 Mo 139 Tc 136 Ru 134 Rh 134 Pd 137 Ag 144 Cd 154 La 187 Hf 158 Ta 146 W 139 Re 137 Os 135 Ir 136 Pt 138 Au 144 Hg 157 Consider 3d series, atomic radius decreases Sc to Cr because of increase in nuclear charge, whereas from Cr to Ni, there is no considerable decrease in atomic radii values because of shielding effect or screening effect of penultimate shell d-electrons. For Cu and Zn, again atomic radius increased because of more number of d-orbital electrons Same trend is applicable for the atomic radii of 4d series Atomic radii increase from first (3 d ) to the second (4 d ) series of the elements but the radii of the third (5 d ) series are virtually the same as those of the corresponding members of the second series except lanthanum because of absence of electrons in its 4f shell This phenomenon is associated with the intervention of the 4 f orbitals which must be filled before the 5 d series of elements begin. The filling of 4 f before 5 d orbital results in a regular decrease in atomic radii called lanthanoid contraction which essentially compensates for the expected increase in atomic size with increasing atomic number.

15. Ionization energy or ionization enthalpy of transition elements Ionization energy is the energy required to remove the outermost, or least bound, electron from an isolated gaseous atom of the element. On the periodic table, first ionization energy generally increases as you move left to right across a period The first ionization energy of an element is the energy needed to remove the outermost, or highest energy, electron from a neutral atom in the gas phase Ionization energy is always positive Consider, First Ionization energy, M + ∆H 1st → M + + e – Second Ionization energy, M + + ∆H 2nd →M 2+ + e – and so on. Removal of 2 nd electron from M+ ion requires more energy Hence ∆H 1st < ∆H 2nd < ∆H 3rd <….< H nth In general, ionization energy depends on two factors: 1) The force of attraction between electrons and the nucleus and (2) the force of repulsion between electrons. The effective nuclear charge felt by the outermost electrons will be less than the actual nuclear charge. This is because the inner electrons will shield the outermost electrons by hindering the path of nuclear charge. This effect is known as the shielding effect General periodic trends: In a group, while moving from top to bottom it decreases. It increases from left to right across a period. Atomic radius decreases, nuclear force of attraction increases, ionization energy also increases

16. Some of the factors which governs ionization energy or ionization enthalpy The force of attraction between electrons and the nucleus. The force of repulsion between electrons. The effective nuclear charge felt by the outermost electrons will be less than the actual nuclear charge. This is because the inner electrons will shield the outermost electrons by hindering the path of nuclear charge. This effect is known as the shielding effect. 

17. Because of shielding effect of d-electrons, increase in ionization energy of 3d series follows only irregular trend The doubly or more highly charged ions have d n configurations with no 4 s electrons. A general trend of increasing values of second ionisation enthalpy is expected as the effective nuclear charge increases because one d electron does not shield another electron from the influence of nuclear charge because d -orbitals differ in direction in general, we can conclude that the uni positive ions furnish d n  configuration with no 4s electrons. Thus, there is reorganisation energy accompanying ionisation with some gains in exchange energy as the number of electrons increases from the transfer of s electrons into d orbitals. Value of IE depends on ( i ) Attractive and repulsive force (ii) Exchange energy Loss of exchange energy increases stability thereby increases ionization energy Consider the electronic configuration of Mn + - 3d 5 4s 1 , where the removal of second electron from 4s 1 is easy, thereby lesser ionization energy required, whereas in Cr + whose electronic configuration is 3d 5 , the removal of second electron is difficult because of its stable configuration, hence more ionization energy required compared to Mn + Ionisation enthalpy/IE/kJ mol –1 IE I 631 656 650 653 717 762 758 736 745 906 IE II 1235 1309 1414 1592 1509 1561 1644 1752 1958 1734 IEIII 2393 2657 2833 2990 3260 2962 3243 3402 3556 3837

18. Similarly, consider the electronic configuration of Mn 2+ - 3d 5 , where the removal of third electron from stable 3d 5 configuration is difficult, thereby higher ionization energy required, whereas in Fe 2+ whose electronic configuration is 3d 6 , the removal of third electron is easy thereby it attains stable configuration, hence lesser ionization energy required compared to Mn 2+ IE is mainly used to predict the thermodynamic stability of compounds Consider Ni = IE1 +IE2 = 737 + 1753 = 2490 kJ/ mol Pt = IE1 +IE2 = 864 + 1791 = 2655 kJ/ mol Hence Ni 2+ compounds are thermodynamically more stable than Pt 2+ compounds Consider the electronic configuration of Cr + - 3d 5 and Cu + - 3d 5 where the removal of second electron from 3d 5 and 3d 10 is difficult, because of its stable configuration, hence more ionization energy required. But the removal of 2 nd electron from Zn + - 3d 10 4s 1 is easy thereby it attains stable configuration .

19. Oxidation state of d-block elements They exhibit variable valency due to involvement of (ns) and (n-1)d electrons. Due to less energy difference between these electrons. The general and common +2 oxidation state is due to s-electron (except Sc in 3d series), while the higher oxidation states (+3 to +7) are because of the loss of both s-and d-electrons The s-electron or the lower OS - ionic bonding Higher OS due to d-electrons - covalent bonding Mn shows highest no. of OS (+2 to +7) Highest oxidation state is +8 – Ru & Os. Greatest no. of OS occur in or near the middle of the series Lesser no. of OS exists - extreme ends – Bcz few e - to lose or share (Sc, Ti) or too many d e - s for higher valence.Cu , Zn bcz of fewer orbitals available Stability of Ti 4+ (3d ) > Ti 3+ (3d 1 ), Mn 2+ (3d 5 ) > Mn 3+ (3d 4 ) Highest oxidation state of transition elements can be calculated by n + 2 where (n = number of unpaired electrons) It is not applied for Cr and Cu. d d 5 or d 10 are more stable - Sc +3 , Ti +4 , Fe +3 , Mn +2 , Zn +2 In aqueous medium Cr +3 is stable, Cr3+ is more stable in aqueous solution due to higher hydration energy which is due to smaller size and higher charge. Co +3 and Ni +2 are stable in complexes Cu +1 < Cu +2 disproportionation reaction in aq. medium Common OS shown by elements, Sc, Y, La and Ac is +3 as their divalent cpds are highly unstable Zero OS in carbonyl cpxes – Ni(CO) 4 Lower OS Ex: Ti +2 , V +2 , Fe +2 , Co +2 etc are reducing agents Higher OS , Ex: Cr +6 , Mn +7 , Mn +6 , Mn +5 , Mn +4 etc are oxidising agents https://selfstudypoint.in/transition-elements-d-block-general-properties/

20. Mo vi O 4 2- , W vi O 4 2- & Re vii O 4 2 – more stable – Higher OS Cr vi O 4 2- & Mn vii O 4 - - strong oxidizing agents Lower OS - Reducing states – Do not form fluorides or oxides Higher OS – Oxidizing states – Form fluorides or oxides V form VF 5 & VCl 5 bcz unable to oxidize highly electronegative & small anion F – but doesn’t form VBr 5 & VI 5 – Bcz + 5 OS of V is strong oxidizing agent thus convert Br – & I – to Br 2 & I 2 Similarly highly electronegative and small O 2– ion formed oxides Ex. VO 4 3 – , CrO 4 2– & MnO 4 – etc. +2 +3 +4 +5 +6 +7 TiCl 2 TiCl 3 TiCl 4 VCl 2 (Ionic, basic) VCl 3 (Less ionic ( Amphoteric ) VCl 4 (Covalent and Acidic, (Strong lewis acid) VOCl 3 TiO Ti 2 O 3 TiO 2 VO V 2 O 3 V 2 O 5 CrO Cr 2 O 3 CrO 3 MnO ( Ionic, basic) Mn 2 O 3 (Less ionic ( Amphoteric ) MnO 2 (Less ionic ( Amphoteric ) MnO 3 (Acidic, covalent) Mn 2 O 7 (Acidic, covalent)

21. Oxidation States of the first row Transition Metals (the most common ones are in bold types) Maximum oxidation state is equal to the sum of unpaired electrons in d-orbital and number of paired electrons in s-orbital. (This is applicable except Cr and Cu) VCl2 is ionic,VCl3 is less ionic while VCl4 is covalent. As the oxidation state of the transition metal increases, the charge density on the metal also increases. This results in the increase of the polarization of the anion charge cloud by the metal and hence covalent character increases ( Fajan's Rules).

22. Colour of d-block elements Most of the transition metal ions – Colour property – Due to d-d transition of unpaired electrons in t 2 g and eg states The electrons from t 2 g set get excited to higher energy set i.e., eg set. This excitation of electrons is called as 'd-d' transition. Hence less amt of energy required - Absorb visible region of light exhibiting colour – Ex. Sc +2 : [Ar]3d 1 , Ti +2 : [Ar]3d 2 , V +2 :[Ar]3d 3 d and d 10 - no colour property - Ex. Sc +3 : [Ar]3d , Ti +4 : [Ar]3d , Cu + :[Ar]3d 10 – Colourless A transition metal ion absorbs a part of visible region of light and emits rest of the colours , the combination of which, is the colour of emitted light. The colour of metal ion is the colour of the emitted light.

23. Transition metal organometallic compounds mainly belong to any of the three categories. Class I  complexes for which the number of valence electrons do not obey the 18 VE rule. Class II  complexes for which the number of valence electrons do not exceed 18. Class III  complexes for which the valence electrons exactly obey the 18 VE rule. In class I complexes, the Δ o  splitting is small and often applies to  3d  metals and σ ligands at lower end of the spectrochemical series. In class II complexes, the Δ o  splitting is relatively large and is applicable to  4d  and  5d  transition metals having high oxidation state and for σ ligands in the intermediate and upper range of the spectrochemical series.  In class III complexes, the Δ o  splitting is the largest and is applicable to good σ donor and π acceptor ligands like CO, PF 3 , olefins and arenes located at the upper end of the spectrochemical series.

24. Factors affecting the colour of complex The colour of a transition metal complex depends on Δ - the magnitude of energy difference between the two d-levels An increase in the magnitude of Δ decreases the wave length (λ) of the light absorbed by the complexes - Δ α 1/λ Thus with a decrease in the λ, the colour of complex changes from Red to Violet KMnO 4 (dark pink), K 2 Cr 2 O 7 (orange) having d configuration but they are coloured due to charge transfer spectrum and charge is transferred from anion to cation . Complex ions [C [Co(H 2 O) 6 ] 3+ + [Co(NH 3 ) 6 ] 3+ [Co(CN) 6 ] 3– O)6]3 Ligand field strength H 2 O < NH 3 < CN - Magnitude of Δ H 2 O < NH 3 < CN - Magnitude of λ H 2 O > NH 3 > CN - Colour of the transmitted light Orange Green-blue Violet Colour of absorbed light (I.e. colour of the complex Green-blue Orange Yellow-green

25. Magnetic property of d-block elements Generally transition elements exhibits the magnetic property Paramagnetic substance - attracted into a magnetic field & due to the presence of unpaired electron. It varies inversely with temperatures. Diamagnetic substance - slightly repelled by a magnetic field. It is independent of temperature. Ferromagnetic – Attracted strongly – type of paramagnetism . Most of the transition metal ions are paramagnetic - Ex.Ti +2 [Ar]3d 2 , Ti +3 [Ar]3d 1 , V +2 [Ar]3d 3 , Cr +3 [Ar]3d 3 3d and 3d 10 configuration - diamagnetic nature. The total magnetic moment of a substance is the resultant of the magnetic moments of all the individual electrons. The magnetic moment created due to spinning of unpaired electrons can be calculated by using Where - 'n' is the number of unpaired electrons in the metal ion. Μ = Magnetic moment in Bohr Magnetons (B.M.) The magnetic moment of diamagnetic substances will be zero. d 5 configuration will have maximum no. of unpaired electrons - maximum paramagnetic in nature.

26. The magnetic properties of complexes of transition metals depend on the nature of the ligands and the oxidation state of the metal. In general, complexes of transition metals with low oxidation states are more likely to be magnetic than those with high oxidation states. The magnetic properties of a complex also depend on the type of ligand . Complexes with ligands that are strongly electron-donating are usually less magnetic than those with ligands that are electron-withdrawing. Iron, cobalt and nickel are together called the iron triads and these metals are ferromagnetic. The unpaired electrons in the d orbitals collect in large numbers of atoms and line up with parallel spins in regions called domains. These domains become ordered when they are exposed to an external magnetic field. The magnetism can remain after the magnetic field is removed. Both Zn atoms and Zn 2+ ions are diamagnetic: Zn atoms [ Ar ]4s 2 3d 10  and Zn 2+  ions [ Ar ]4s 3d 10 Ag forms both Ag +  ions and, rarely, Ag 2+  :Ag atoms [Kr]5s 1 4d 10  are paramagnetic, Ag +  ions [Kr]4d 10  are diamagnetic and Ag 2+  ions [Kr]4d 9  are paramagnetic.

27. Catalytic property of d-block elements Transition elements and their compounds exhibit catalytic properties. This is due to their variable valency as well as due to the free valencies on their surface. When transition elements and their compounds are in powdered state, their catalytic properties exhibited will be to a greater extent. This is due to greater surface area available in the powdered state. Reason : This activity is ascribed to their ability to adopt multiple oxidation states and to form complexes. First row transition metals utilise 3d and 4s electrons for bonding, this has the effect of increasing the concentration of the reactants at the catalyst surface and also weakening of the bonds in the reacting molecules (the activation energy is lowering). Also because the transition metal ions can change their oxidation states, they become more effective as catalysts. Transition metals and their compounds exhibiting catalytic properties in various processes are-

28. Tendency to form complexes Transition elements form complexes readily because of the small size of the ions and higher nuclear charge, they possess high charge density. Due to the presence of vacant d- orbitals in which a ligand can donate its electron, forms a complex. Transition metal ions have a large polarizing power as a result they can attract lone pairs from other atoms to form complexes. For example, elements like Fe +2 and Fe +3 , Cu + and Cu +2  shows variable oxidation state and can form a large number of complexes Transition elements have a tendency to form complexes more than s and p block elements So they are able to form complexes with the groups which are able to donate an electron pair The cations of d-block elements have a strong tndency to form complexes Transition elements are the more reactive due presence of vacant d-orbital. The presence of 5d orbitals , which can accommodate a total of 10 electrons, in each transition metal atom helps it accept the electrons donated by the electron-rich ligands since the donated electrons can be accommodated in the vacant d orbitals of the transition metal atom.

29. Interstitial compounds Interstitial compounds are those which are formed when small atoms like H, C or N are trapped inside the crystal lattices of metals They are usually non stoichiometric and are neither typically ionic nor covalent, for example, TiC , Mn 4 N, Fe 3 H, VH 0.56 and TiH 1.7 , etc. Hence it is chemically non-reactive The formulas quoted do not, of course, correspond to any normal oxidation state of the metal. Because of the nature of their composition, these compounds are referred to as interstitial compounds. The principal physical and chemical characteristics of these compounds are as follows: ( i ) They have high melting points, higher than those of pure metals. (ii) They are very hard, some borides approach diamond in hardness. (iii) They retain metallic conductivity. (iv) They are chemically inert. As vacant spaces of the transition metals are filled up by small atoms, these compounds are hard and rigid. The chemical properties of the parent transition metals are not altered during the formation of interstitial compounds. However, there are various changes in the physical properties such as density, rigidity, hardness, malleability, ductility, electrical conductivity etc. Steel and cast iron are the interstitial compounds of iron which are formed with carbon. In the formation of these compounds, the malleability and ductility of iron are lost to a great extent, but the tenacity of the metal increases.

30. Titanium carbide Titanium carbide, with chemical formula TiC , crystallizes in the cubic system: (Z = 4). The lattice constant is a = 0.4327 nm. Ti atoms occupy the origin positions (0,0,0), however, C atoms are located in (1/2,1/2,1/2) positions. Ti and C atoms are octahedrally coordinated with each other; consequently, Ti 6 C octahedra share edges C atoms occupy the octahedral positions. Thus, if viewed along the direction perpendicular to the planes, Ti and C atoms form a hexagonal shape Titanium carbide occurs in nature as a form of the very rare mineral khamrabaevite [( Ti,V,Fe )C].

31. Furthermore, TiC powder was commercially produced primarily by the reduction of TiO 2 by carbon, especially carbon black, in a temperature range 1700-2100 o C and long reaction times (10-24 h) The chemical reaction in the carbothermal reduction is given by: TiO 2 (s) + 3C(s) ↔ Ti(s) + 2CO(g)

32. Chemical vapor deposition technique (CVD) Chemical vapor deposition technique (CVD) is the deposition of a solid on the heated substrate from reactants in the vapor phase. The chemical reactions involved in the precursor to material conversion can include thermolysis , hydrolysis, oxidation, reduction, nitration, and carboration depending on the precursor species used Once the gaseous species are in proximity to the substrate or the surface itself, they can either adsorb directly on the catalyst particle or on the surface. Diffusion processes, as well as the concentration of the adsorbates , are responsible for the growth of a solid phase at the catalyst-surface interface. Generally, the deposition of carbides was obtained by reacting a halide with a hydrocarbon using hydrogen or nitrogen gas. Noel and Kovar (2002) synthesized TiC nanoparticles using CVD technique from the deposition of titanium and carbon powders on tantalum using hydrogen gas, titanium tetrachloride (TiCl 4 ) and either methane (CH 4 ) or acetylene (C 2 H 2 ) source gases. Amorphous fine titanium carbide powders have been prepared by CVD in the TiCl4-CH4 system at temperature ranging from 850 to 1050 °C in hydrogen atmosphere with pressure varying from less than 100 Pa to 1 atm , as given in the following reaction : TiCl 4 (g) + CH 4 (g) + H 2 (g) → TiC (s) + 4HCl(g) + H 2 (g) The final product of this reaction is a hard and wear-resistant coating that exhibits a chemical bond to the substrate

33. Mg-thermal reduction Nanostuctured titanium carbides were synthesized by liquid magnesium reduction of vaporized TiCl 4 + CCl 4 solution Fine TiC particles were obtained from Ti and C, and vacuum was used to remove the residual phases of MgCl 2 and excess Mg. Mechanical alloying (MA) Formation of nanocrystalline TiC by MA of Ti and activated carbon powders can be carried. During the initial stage of milling, the carbon powders are crushed into smaller particles and the titanium particles are deformed and fragmented caused by plastic deformation induced during MA. In this stage, no TiC can be formed. During the second stage of milling, with increasing milling time, the titanium and carbon powders are refined: the fine particles of carbon are entrapped between the big particles of titanium. In addition, no TiC can be formed During the third stage of milling, a little amount of TiC was formed on the surface of the Ti particles caused by defects. Finally, the as-milled products are completely composed of nanocrystalline TiC powder

34. Industrial Uses of TiC Titanium carbide attracted great interest for several structural applications. Therefore, TiC can be used in cutting tools because of its combination of wear resistance and high hardness It can also be used as a coating for abrasive steel bearings and wear resistant tools. In addition, it can be used to enhance the conductivity of materials and as a nucleating agent In the middle of the 1960s, the wear resistance of such tools was increased appreciably by the deposition of thin coatings of TiN , TiC , and other refractory compounds The increase in the lifetime of the tools due to such coatings depends on the improved wear resistance and the lower cutting temperature due to a reduced friction between the tool and the work material During the last years, the domains of application for these coatings have been extended to ordinary steel tools and high-speed steels. Commercially, high-speed steel drills coated with TiN have been introduced The wear life of such coated drills is 4 to 6 times longer than that of uncoated drills. In addition, coated drills show better resistance to corrosion and erosion TiC are also used in electronic devices, as diffusion barriers in integrated circuits, molded bipolar plates for high-voltage battery, and fuel power sources Moreover, TiC is employed as coatings for pump shafts, packing sleeves, feed screws for the chemical industry, as coatings for molding tools, and kneading elements for plastic processing They are also utilized as coatings for fusion-reactor applications. TiC is very suitable for use high-speed cutting tool applications for reducing thermal stresses and cracking Furthermore, TiC is effectively utilised in cermets due to its low friction coefficient and higher oxidation resistance compared to cemented tungsten carbide TiC is also widely used in different branches of machine construction due to its high strength and hardness Titanium nitride ( TiN ) has an attractive yellow colour that is used in jewelry and decorative glass coatings. The high hardness of this compound has also made it very attractive as a coating to extend the life of tools The titanium aluminide intermetallic compounds Ti 3 Al and TiAl have attractive engineering properties that make them potential replacements for nickel-based superalloys in aircraft engines at temperatures from 600 to 870°C (1,100 to 1,600 °F) A major impediment to wider use is their low ductility

35. Manganese Nitride Powder Application Used for production of special alloy steel, high strength steel, stainless steel, heat-resistant steel products Application in the field of high nitrogen steel smelting Used as the steel-making additive and endow many excellent performances to steel grade such as strength, toughness, creep resistance, etc. Specialty demonstrated its good market prospects in large diameter steel pipe of transmitting oil and gas strength steel in shipbuilding and automotive.

36. Interstitial hydrides Metallic hydrides (also called as interstitial hydrides) are composed of transition metals and hydrogen bonds. These hydrides have the unusual and unique property of being nonstoichiometric , which means that the proportion of H atoms to metals is not fixed. The composition of nonstoichiometric substances varies. The concept and foundation for this is that with metal and hydrogen bonding, there is a crystal lattice that H atoms can and may fill in between, however this is not a certain ordered filling. As a result, the proportion of H atoms to metals is not constant. Metallic hydrides do, however, contain more basic stoichiometric molecules. Examples of interstitial hydrides: LaH 2.87 , YbH 2.55 , NiH 0.6–0.7 , and PdH 0.6–0.8  are examples of interstitial hydrides. Interstitial hydride or metallic hydrides are formed by the elements of group 3,4,5,10,11,12, d-block and f-block elements. From group 6 only Cr forms the hydride and metals of groups 7,8 and 9 do not form hydrides. This region which does not form hydrides is called a hydride gap. Interstitial hydrides are called as such, because in these compounds, hydrogen occupies the interstitial sites in the metal lattice without changing the type of the lattice .

37. https://onlinelibrary.wiley.com/doi/abs/10.1002/9781119951438.eibc0022#:~:text=Borides%20are%20to%20some%20extent,atoms%20in%20metal%2Drich%20compounds.

38. Toxicity of Mercury Mercury (Hg) is found in air, water, and soil and exists in three forms: elemental or metallic mercury (Hg ), inorganic mercury (Hg + , Hg 2+ ), and organic mercury (commonly methyl or ethyl mercury) Elemental mercury is liquid at room temperature and can be readily evaporated to produce vapor Mercury vapor is more hazardous than the liquid form. Inhaling large amounts of Hg vapor can be fatal Organic mercury compounds such as methyl mercury (Me-Hg) or ethyl mercury (Et-Hg) are more toxic than the inorganic compounds The order of increasing toxicity related to different forms of mercury is defined as Hg  < Hg 2+ , Hg +  < CH 3 -Hg https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8078867/

39. Elemental mercury poisoning symptoms Elemental mercury is usually harmless if you touch or swallow it because its slippery texture won’t absorb into your skin or intestines. Elemental mercury is extremely dangerous if you breathe it in and it gets into your lungs. Often, elemental mercury becomes airborne if someone is trying to clean up a mercury spill with a vacuum. Symptoms of elemental mercury poisoning occur immediately after inhaling the chemical and include: Coughing. Trouble breathing. Metallic taste in your mouth. Nausea or vomiting. Bleeding or swollen gums. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8078867/

40. Inorganic mercury poisoning symptoms Inorganic mercury is poisonous when swallowed. When the chemical enters your body, it travels through your bloodstream and attacks your brain and kidneys. Symptoms of inorganic mercury poisoning include: Burning sensation in your stomach and/or throat Nausea or vomiting Diarrhea Blood in vomit or stool Urine color changes - urine colour changes can also be caused by conditions like urinary tract infections, liver failure and kidney stones

41. Organic mercury poisoning symptoms Organic mercury causes symptoms if you inhale it (breathe it in) or touch it. Symptoms don’t occur immediately and usually arise after long periods of contact (could be years or decades) with the compound. Symptoms of organic mercury poisoning from long-term exposure include: Feeling numb or dull pain in certain parts of your body. Tremors (uncontrollable shaking). Unsteady walk. Double vision or blurry vision; blindness. Memory loss. Seizures. People who are pregnant and exposed to large amounts of methylmercury (a type of organic mercury) can cause brain damage to developing fetuses. Most healthcare providers recommend people who are pregnant eat a limited amount of fish or remove fish from their diet, especially swordfish, during their pregnancy. Long-term organic mercury exposure is deadly. If you frequently come into contact with organic mercury, wear proper personal protective equipment, like a mask and gloves, to reduce your risk of health problems associated with the compound.

42. Causes of mercury poisoning Inhaling mercury vapor (small droplets of mercury that become airborne and enter your lungs). Eating fish or seafood that naturally contains large amounts of organic mercury. Swallowing mercury. Touching liquid mercury. https://my.clevelandclinic.org/health/diseases/23420-mercury-poisoning

43. Symptoms of Mercury Poisoning Vision, speech, hearing and walking impairment Numbness in hands, feet and sometimes around the mouth Uncoordinated movement Muscle weakness Skin rashes Mood swings, memory loss and mental disturbances

44. Toxicity of Cadmium Cadmium ( Cd ) is a naturally occurring metal situated in the Periodic Table of the Elements between zinc (Zn) and mercury (Hg), with chemical behavior similar to Zn. It generally exists as a divalent cation , complexed with other elements (e.g., CdCl 2 ). Cd exists in the earth’s crust at about 0.1 part per million, usually being found as an impurity in Zn or lead ( Pb ) deposits, and therefore being produced primarily as a byproduct of Zn or Pb smelting. Human exposure to Cd occurs chiefly through inhalation or ingestion. Ten to fifty percent of inhaled cadmium dust is absorbed, depending on particle size. Absorption through skin contact is negligible. About five to ten percent of ingested Cd is absorbed, also depending on particle size. Intestinal absorption is greater in persons with iron, calcium, or zinc deficiency https://www.hindawi.com/journals/tswj/2013/394652/

45. Cigarette smoking is considered to be the most significant source of human cadmium exposure [4]. Blood and kidney Cd levels are consistently higher in smokers than nonsmokers. Inhalation due to industrial exposure can be significant in occupational settings. for example, welding or soldering, and can produce severe chemical pneumonitis [3]. Cadmium exposure occurs from ingestion of contaminated food (e.g., crustaceans, organ meats, leafy vegetables, rice from certain areas of Japan and China) or water (either from old Zn/ Cd sealed water pipes or industrial pollution) and can produce long-term health effects. Contamination of drugs and dietary supplements may also be a source of contamination

46. Symptoms or health effect of Cadmium poisoning When eaten, large amounts of cadmium can severely irritate the stomach and cause vomiting and diarrhea. Breathing high levels of cadmium damages people’s lungs and can cause death. Exposure to low levels of cadmium in air, food, water, and particularly in tobacco smoke over time may build up cadmium in the kidneys and cause kidney disease and fragile bones. Cadmium is considered a cancer-causing agent.

47. Toxic metal Organ toxicity Disrupted macromolecule/mechanism of action References Mercury (Hg) - CNS injuries - Thiol binding Cheng et al., 2006 ;  Bottino et al., 2016 ;  Chen R. et al., 2019 ;  Zhang et al., 2020 - Renal dysfunction - Enzymes inhibition - GI ulceration - ROS production - Hepatotoxicity - Aquaporins mRNA reduction - Glutathione peroxidase inhibition - Increased c- fos expression Lead ( Pb ) - CNS injury - Increased inflammatory cytokines IL-1β, TNF-α, and IL-6 in the CNS Struzynska et al., 2007 ;  Dongre et al., 2011 ;  Wang et al., 2013 ;  Boskabady et al., 2016 - Lungs dysfunction - Increased serum ET-1, NO, and EPO - Hematological changes (Anemia) - Inactivation of δ-ALAD and ferrochelatase (inhibition of heme biosynthesis) - GIycolic - Reduced GSH, SOD, CAT, and GPx levels - Liver damage - Reduced pulmonary function - Cardiovascular dysfunction Chromium (Cr) - Kidney dysfunction - DNA damage Deng et al., 2019 ;  Pavesi and Moreira, 2020 - GI disorders - Genomic instability - Dermal diseases - Oxidative stress and ROS generation - Increasing the incidence of cancers including lungs, larynx, bladder, kidneys, testicular, bone, and thyroid Cadmium ( Cd ) - Degenerative bone disease - miRNA expression dysregulation Schutte et al., 2008 ;  Pan et al., 2013 ;  Pi et al., 2015 ;  Fay et al., 2018 ;  Wang Y. et al., 2018 - Kidney dysfunction - Apoptosis - Liver damage - Endoplasmic reticulum stress - GI disorders - Cd -MT absorption by the kidneys - Lungs injuries - Dysregulation of Ca, Zn, and Fe homeostasis - Disorders in the metabolism of Zn and Cu - Low serum PTH - Cancer - ROS generation https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8078867/table/T1/?report=objectonly