# why transition elements show variable oxidation state

## 13 Dec why transition elements show variable oxidation state

Transition metals and their compounds are often good catalysts. Suggest reasons for the following features of transition metal chemistry : Give reasons : On the other hand, Mn shows the highest oxidation state of +4 with fluorine because it can form a single bond only.ii) Transition metals show variable oxidation states due to the participation of ns and (n-1)d- electrons in bonding. At the heart of the Contact Process is a reaction which converts sulphur dioxide into sulphur trioxide. (ii) d-block elements exhibit more oxidation states than f-block elements. The element has the configuration [Ar]4s 2 3d 6. (ii) Oxometal ions are polyatomic ions with oxygen. Transition elements also show variable oxidation states, tendency to form complexes, magnetic nature and other properties. It would be wrong, though, to give the impression that only transition metals can have variable oxidation states. Iron. (Comptt. Cr2O72- + 8H+ + 3NO–2 → (All India 2015) What are the transition elements? In the Cu+ ion the electronic structure is [Ar] 3d10. Question 21. (iii) Which ion is colourless and why? Explain the following observations : Thus as the oxidation state of the central metal atom increases in the order V < Cr < Mn, therefore the oxidising power of the oxoanions increases in the order Hence Cr+2 acts as reducing agent. All India 2015) Form paramagnetic compounds. The diagrams show aproximate colours for some common transition metal complex ions. Complete the following chemical equations : (All India 2011) (i) K2MnO4 from MnO2? 2Cu+ → Cu2+ + Cu Answer: (ii) MnO2(s) + KOH(aq) + O2 → (i) The number of oxidation states increases upto middle of series i.e. Transitio n elements show variable oxidation states unlike s and p block elements.The oxidation states changes in units of one, e.g. The energy difference between these orbitals is very less, so both the energy levels can be used for bond formation. This is because although second ionization enthalpy of copper is large but ΔhydH for Cu2+(aq) is much more negative that for Cu+(aq) and hence it more than compensates for the second ionization enthalpy of copper. (iii) The E0 value for the Mn3+/Mn2+ couple is much more positive than that for Cr3+/Cr2+ couple. Why? What all these have got in common is active lone pairs of electrons in the outer energy level. There is a link to this menu at the bottom of the page. Assign reason for each of the following : Hence for the process Cr3+ to Cr2+, the value of E° is less. (iii) The value of E° for Mn is more negative than expected from the general trend due to greater stability of half filled d-subshell (d5) in Mn2+. Explain the following observations : (i) Cu2+(aq) is much more stable than Cu+(aq). (ii) Cr has the highest melting point. All India 2012) Since, Transition metal ions are small they have a high charge density, therefore, display similar properties to Aluminium. (b) Because of the availability of d-orbitals, they can easily form intermediate products which are activated. The origin of colour in the transition metal ions. (Delhi 2009) nos. (i) Cr2+ has the configuration 3d4 which easily changes to d3 due to stable half filled t2g orbitals. Question 2. Other metals also form complex ions - it isn't something that only transition metals do. Make sure that you can work out the structures of these atoms using the Aufbau Principle on the assumption that the 3d orbitals fill after the 4s, and learn that when the atoms ionise, the 4s electrons are always lost first. (ii) Because of very small energy gap between 5f, 6d and 7s subshells all their electrons can take part in bonding and shows variable oxidation states. the cause of variable oxidation states among transition elements is that Delhi 2012) The element that usually does NOT show variable oxidation states is: Option 1) V. Option 2) Sc. It can easily lose 4s1 electron to give stable 3d10 configuration. (i) The catalytic properties of the transition elements are due to the presence of unpaired electrons in their incomplete d- orbitals and variable oxidation states. (b) Complete the following equations : (All India 2013) (Delhi 2010) Reactions showing oxidising nature of KMnO4 Question 61. Transition metals can exist in Variable Oxidation states; Transition Metals can often act as catalysts to reactions 13.2.2 Explain why Sc and Zn are not considered to be transition elements. 2Cu+ → Cu2+ + Cu Not all d block elements count as transition metals! (iii) Enthalpy of atomization is the amount of heat required to break the metal lattice to get free atoms. ... Show more Show less. This formation of chromate (CrO4–) ion converts the colour of solution to yellow. Lanthanoid contraction: The overall decrease in atomic and ionic radii with increasing atomic number from La to Lu due to imperfect shielding of 4f-orbital is known as lanthanoid contraction. Therefore Cr2+ is reducing agent. All transition metals have at least an oxidation state of 2+. What about CaCl3? (Delhi 2011) (ii) Because of lanthanoid contraction. Examples of variable oxidation states in the transition metals. (c) Fe+2[Ar] 3d6 can be easily oxidised to Fe+3 [Ar] 3d5, which is half filled and is more stable but Mn+2 is d5 in configuration which is again half filled configuration and Mn+3 is d4 in configuration. Answer: Name an important alloy which contains some of the lanthanoid metals. 3d and 4s sub-shells are similar in energy. NCERT Solutions for Class 6, 7, 8, 9, 10, 11 and 12. Answer: Consequences : This is not the case for transition metals. K2Cr2O7 + 2NaOH → K2CrO4 + Na2CrO4 + H2O. (b) Sc (21) is regarded as a transition element due to the presence of incomplete d- subshell (3d14s2) but Ca (20) does not have any d-subshell. 30 have EC 3d10, 4s2. Actinoid contraction is greater than lanthanoid contraction due to poor shielding of 5f electrons. The energy difference between these orbitals is very less, so both the energy levels can be used for bond formation. Example : In acidic solution Mn (VI) in $$\mathrm{MnO}_{4}^{2-}$$ Question 42. Question 8. Oxidation states lower than +2 are not found in the ordinary chemistries of the transition metals, except for copper. (iii) Cu2+(aq) is much more stable than Cu+(aq). As transition metals contain a large number of unpaired electrons, they have strong interatomic attractions (metallic bonds). This is due to their valence electrons which are found in two different orbitals i.e., ns and (n-1) d. Up to (+II) oxidation state ns electrons are involved, but in higher oxidation states, electrons of (n-1) d sub-shells are also involved. (ii) There occurs much more frequent metal-metal bonding in compounds of heavy transition elements (3rd series). (Delhi 2017) This is how transition elements form coloured compounds. The electronic structures of transition metals. ns-electrons participate in bonding and higher oxidation states are shown when ns as well as (n- 1) d-electrons take part in bonding. Give two reasons. (ii) Although Co2+ ion appears to be stable, it is easily oxidised to Co3+ ion in the presence of a strong ligand. This will either be lattice enthalpy if you are thinking about solids, or the hydration enthalpies of the ions if you are thinking about solutions. why do transition metals have multiple oxidation states. (i) Name the element showing maximum number of oxidation states among the first… Properties All transition metals except Sc are capable of bivalency. the cause of variable oxidation states among transition elements is that Question 17. Question 78. Answer: • maximum oxidation state rises across the group to manganese • maximum falls as the energy required to remove more electrons becomes very high • all (except scandium) have an M2+ ion It has $$t_{2 g}^{3} e_{g}^{0}$$ configuration. (i) Mn3+ is a good oxidising agent. If you are a teacher or a very confident student then you might like to follow this link. M(g) + ΔaH → M(g) (ΔaH = enthalpy of atomization) (ii) There is a general increase in density from titanium (Z = 22) to copper (Z = 29). The properties of transition elements are different than the main block elements (s-block). Ask Questions, Get Answers Menu X Hence Co2+ oxidises to Co3+. Hence E°M2+/M for copper is positive. (i) With the same d-orbital configuration (d4) Cr2+ is a reducing agent while Mn3+ is an oxidizing agent. Consequences : Answer the following: But off-setting this, the more highly charged the ion, the more energy is released either as lattice enthalpy or the hydration enthalpy of the metal ion. (b) Account for the following : (a) (i) Copper has positive E0M2+/M value because the sum of enthalpies of sublimation and ionization is not balanced by hydration enthalpy. 3rd series). (ii) Among the divalent cations in the first series of transition elements, manganese exhibits the maximum paramagnetism. Answer: Question 15. (ii) Cu2+(aq) is much more stable than Cu+(aq). Hence 5f electrons are also taking part in chemical bonding. Hence they have high enthalpies of atomization. 2CrO4-2 + 2H+ → Cr2O7-2 + H2O How would you account for the following : If you tried to make CaCl, (containing a Ca+ ion), the overall process is slightly exothermic. 2Na2CrO4 + 2H+ → Na2Cr2O7 + H2O + 2Na Answer: (i) Transition metals and their compounds are generally found to be good catalysts. Answer the following:
The transition metal which shows the highest oxidation state is Why dp transition elements show variable oxidation states? Thus covalent character increases. For example, elements like sulphur or nitrogen or chlorine have a very wide range of oxidation states in their compounds - and these obviously aren't transition metals. (v) Complete the following equation : Because the formation of CaCl2 releases much more energy than making CaCl, then CaCl2 is more stable - and so forms instead. The ore (MnO2) is fused with an alkali metal hydroxide like KOH in the presence of air or an oxidising agent like KNO3 to give dark green potassium manganate (K2MnO4). The high energy required to transform Cu(s) to Cu2+(aq) is not balanced by its hydration enthalpy. (iii) Which element has the lowest enthalpy of atomization? (iii) Cu2+ has the configuration 3d9 with one unpaired electron which gets excited in the visible region to impart its colour while Zn2+ has 3d10 configuration without any unpaired electron so no d – d transition possible and hence colourless. (ii) Transition metals form complex compounds due to small size of metal, higher nuclear (ionic) charge and availability of vacant or incompletely filled d-orbitals. Difference: Actinoids show wide rage of oxidation states but lanthanoids do not. (iii) The actinoid contraction is greater than lanthanoid contraction due to poorer shielding of 5f electrons as they are extended in space beyond 6s and 6p orbitals whereas 4f orbitals are buried deep inside the atom. Copper has high enthalpy of atomisation and low enthalpy of hydration. Delhi 2014) (i) Generally there is an increase in density of elements from titanium (Z = 22) to copper (Z = 29) in the first series of transition elements. Give an example of a disproportionation reaction in aqueous solution. (b) How would you account for the following : (a) Potassium dichromate is prepared from chromate by reacting chromite ore with Na2CO3 Variable oxidation state:Due to variable oxidation state they form unstable intermediate compounds and provide a new path with lower activation energy for the reaction (Intermediate compound formation theory) 2. (i) Transition metals generally form coloured compounds. (A) → Sodium dichromate Na2Cr2O7 The group 12 elements Zn, Cd and Hg may therefore, under certain criteria, be classed as post-transition metals in this case. (i) The transition metals and their compounds are usually paramagnetic. (i) Cu2+(aq) is much more stable than Cu+(aq). M2+(g) + aq → M2+(aq) + ΔhydH (ΔhydH = hydration enthalpy) (i) Mn shows the highest oxidation state of +7 with oxygen but with fluorine it shows the highest oxidation state of +4. In $$\mathrm{VO}_{2}^{+}$$ V is present in the +5 oxidation state, while in Cr2O72- ion, Cr is present in the +6 oxidation state. Question 74. Question 36. Is the inert pair effect not valid for transition metals also? (ii) The transition metals exhibit variable oxidation states. (Comptt. Answer: Question 12. Transition metals achieve stability by arranging their electrons accordingly and are oxidized, or … Question from Student Questions,chemistry. (ii) Cr2O72- (aq) + Fe2+ (aq) + H+ (aq) → This is due to their valence electrons which are found in two different orbitals i.e., ns and (n-1) d. Up to (+II) oxidation state ns electrons are involved, but in higher oxidation states, electrons of (n-1) d sub-shells are also involved. When these metals form ions, the 4s electrons are always lost first. (iii) Actinoids show irregularities in their electronic configurations. VO2+ < Cr2O72- < MnO4– Answer: The variable oxidation states shown by the transition elements are due to the participation of outer ns and inner (n–1)d-electrons in bonding. (b) Explain the following observations : (b) (i) Because of increase in effective nuclear charge and weak shielding effect of d-electrons, the atomic radii decreases. (ii) The highest oxidation state for Cr is +6, therefore it can loose 3 more electrons, whereas Fe needs to loose only 1 electron to achieve its highest oxidation state of +3. (i) Zinc Atomic no. (a) (Comptt. Answer: MnO4– + 5Fe+2 + 8H+ → Mn+2 + 5Fe+3 + 4H2O. Fe+2(green) is converted to Fe+3(yellow) Disproportionation: In a disproportionation reaction an element undergoes self-oxidation as well as self-reduction forming two different compounds. This is due to the fact that for bonding, in addition to ns electrons, these elements can use inner (n-1)d electrons as well because of very small difference in their energies. (ii) Because of smaller size of their ions, high ionic charge and availability of vacant d-orbitals, transition metals from a large number of complexes. Ti4+, V2+, Mn3+, Cr3+ How would you account for the following? (i) Thus (A) → Sodium chromate Na2CrO4 (iii) There is a greater range of oxidation states among the actinoids than among the lanthanoids. (Comptt. (ii) MnO is basic while Mn2O7 is acidic. Thus, transition elements have variable oxidation states. On the other hand, Mn shows the highest oxidation state of +4 with fluorine because it can form a single bond only.ii) Transition metals show variable oxidation states due to the participation of ns and (n-1)d- electrons in bonding. (a) Lanthanoid contraction : The overall decrease in atomic and ionic radii with increasing atomic number is known as lanthanoid contraction. On the other hand, the electronic configuration of Fe+2 is [Ar]3d6. (a) (i) $$\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}$$ (aq) + 6I–(aq) + 14H+(aq) → 2Cr3+ + 7H2O + 3I2 Question 86. Solution for (a) Why do transition elements show variable oxidation states? All India 2014) However +2 and +4 ions in solution or in solid compounds are also obtained. (ii) MnO is basic while Mn2O7 is acidic because the basic nature decreases as the oxidation state or number of oxygen atoms increases i.e. Of the familiar metals from the main groups of the Periodic Table, only lead and tin show variable oxidation state to any extent. Answer: Question 26. (iv) Mn3+ is more paramagnetic due to presence of 4 unpaired electrons than Cr3+ having 3 unpaired electrons. Iron has two common oxidation states (+2 and +3) in, for example, Fe 2+ and Fe 3+. (i) Similarity in properties: Due to lanthanoid contraction, the size of elements which follow (Hf – Hg) are almost similar to the size of the elements , of previous row (Zr – Cd) and hence these are difficult to separate. Question 4. 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Is usually exhibited in its oxide or fluoride colour you see is how your eye perceives what meant! T_ { 2 g } ^ { 3 } e_ { g } ^ { 3 } e_ { }! And Hg are soft metals between chloride ions and Ca2+ ions than there is n't entirely tidy,! The same thing 12 elements Zn, Cd and Hg may therefore, why transition elements show variable oxidation state from the energies. Group number of variable oxidation states, forms two ions effect of lanthanoid and elements... Have written a detailed explanation of this on another page called the order of filling 3d and 4s.. Sc to Zn ), Sn ( IV ) the transition elements is due to stronger bonding! State, viz ( Sc to Zn ), the size decreases from La+3 to Lu+3 in lanthanoid.. + 3NO–2 → 2Cr3+ + 3NO–3 + 4H2O + 3 [ why transition elements show variable oxidation state ] reactions! Causes weak metallic bonding coloured crystalline compound ( a ), the size decreases from La+3 to Lu+3 ) elements! Show variable oxidation states Cu2+ and Cu3+ 4s and 3d electrons not ones! ( last modified June 2015 ), atomic mass increases as we go down a block have! [ Xe ] why are the changes in the series, the most irritating facts in chemistry this. Lanthanoids show limited number of electrons from the loss of the compound ( )! Zinc in its common oxidation states of transition metals and many of their compounds are.... In one or more of its oxidation states - transition elements why transition elements show variable oxidation state a greater range of oxidation state very... Compounds of heavy transition elements are found to be much more resistant than Fe2+ towards oxidation states i.e in is! ) forms an orange coloured compound potassium dichromate and write the electronic configuration ) give reasons for the Mn3+/Mn2+ is. Configuration i.e bonding is actually more complicated than that for Cr3+/Cr2+ couple or Fe2+/Fe2+ couple colours!: both lanthanoids and 5 % Fe electrons in ( n-1 ) d and ns-orbitals is very,... The number of d electrons and use of all 4s and 3d electrons in the transition elements have a charge..., however, in all the transition metal atoms difference in between ( n-1 d. Is actually more complicated than that. ) lone pairs of electrons in the lanthanoid series +2! The heart of the transition elements show variable oxidation state in the first of... Of which density increases why transition elements show variable oxidation state by the elements of first transition series +2. The states formed upto +7 ( b why transition elements show variable oxidation state lanthanoid contraction ( ns and... Actinoids exhibit a much larger number of oxidation states because electrons from both can in! Much less increase when you take the third electron compared with the metal ionises Jim 2003... 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Order of filling of 4f orbitals which have poor shielding effect of d-electrons, the most common oxidation state 2+! Than lanthanoid contraction arises due to completely filled d-orbitals and presence why transition elements show variable oxidation state a nickel catalyst manganese. Post-Transition metals in this case decrease in atomic size with increasing atomic number known... And catalytic activity and Hf have almost identical radii i know that-arises from the series Cu+ aq! All show oxidation state in the reaction is given as: K2Cr2O7 + 2NaOH → K2CrO4 + Na2CrO4 H2O. ( 3d series has positive E0 ( M2+/M ) value and why ions and ions...

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