Transition metals and their compounds function as catalysts either because of their ability to change oxidation state or, in the case of the metals, to adsorb other substances on to their surface and activate them in the process. This produces the dark green K2MnO4 which disproportionates in a neutral or acidic solution to give KMnO4 (Delhi 2016) The colour you see is how your eye perceives what is left. (iii) The members in the actinoid series exhibit a larger number of oxidation states than the corresponding members in the lanthanoid series. Consequences : 3rd series). Variable oxidation states may be understood rather better by a consideration of the electronic configurations of the states formed. Manganese has a very wide range of oxidation states in its compounds. (iv) The variation in oxidation states of transition metals is of different type from that of the non-transition metals. All transition metals have at least an oxidation state of 2+. (i) The gradual decrease ‘n’ size (actinoid contraction) from element to element is greater among the actinoids than that among the lanthanoids (lanthanoid contraction). Answer: Similarity : Both lanthanoids and actinoids show contraction in size and irregularity in their electronic configuration. Answer: While Mn2+ has stable half filled d5 configuration. Example: Zr and Hf are known as chemical twins due to their similar radii. The Sc3+ ion has no d electrons and so doesn't meet the definition. The zinc ion, Zn2+, has a completely filled d-orbital and so it's not a transition metal. Other metals also form complex ions - it isn't something that only transition metals do. Potassium Permangante (KMnO4) is prepared from pyrolusite ore (MnO2). (a) Potassium dichromate is prepared from chromate by reacting chromite ore with Na2CO3 (a) How would you account for the following : (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. It has completely filled ‘d’ orbitals. 2Cu+ → Cu2+ + Cu It is the only metal in the first series of transition elements showing this type of behaviour. (i) Due to lanthanoid contraction in second series after lanthanum, the atomic radii of elements of second and third series become almost same and hence show similarities in properties. (Delhi 2012) Solution for (a) Why do transition elements show variable oxidation states? (i) Cr+2 is reducing agent as its configuration changes from d4 to d3 which is having half filled t2g level whereas Mn+3 to Mn+2 results in stable half filled d5 configuration hence it is oxidising. The obvious explanation is that chromium takes up this structure because separating the electrons minimises the repulsions between them - otherwise it would take up some quite different structure. (iii) Lanthanoids form primarily +3 ions, while the actinoids usually have higher oxidation states in their compounds, +4 or even +6 being typical. Answer: (iii) The catalytic properties of the transition elements are due to the presence of unpaired electrons in their incomplete d-orbitals and variable oxidation states. How does the acidified permanganate solution react with oxalic acid? (ii) Copper has positive E0(Cu2+/Cu) value because of its high enthalpy of atomization and low enthalpy of hydration. Describe the oxidising action of potassium dichromate and write the ionic equations for its reaction with Delhi 2014) Thus Cr3+ is more stable than Mn3+. Because the formation of CaCl2 releases much more energy than making CaCl, then CaCl2 is more stable - and so forms instead. But you then have to look at why it is stable. (i) Conversion of Mn02 into potassium manganate : (iii) The enthalpies of atomization of the transition metals are high. (ii) Due to presence of more unpaired electrons and use of all 4s and 3d electrons in the middle of series. Question 9. (b) Account for the following : Write its two consequences. Due to small change in atomic radii, the chemical properties of lanthanoids are very similar due to which separation of lanthanoid becomes very difficult. Question 26. Also, these first transition series elements create ions with a charge of 2+ or 3+. Transition elements exhibit a wide variety of oxidation states in their compounds. Hence Mn3+ easily changes to Mn2+ and acts as oxidising agent. It also has a less common +6 oxidation state in the ferrate(VI) ion, FeO42-. (i) Zirconium (Z = 40) and Hafnium (Z = 72) have almost similar atomic radii. Transition metals in low oxidation states have lower electronegativity values than oxygen; therefore, these metal oxides are ionic. (i) Mn2+compounds are more stable than Fe2+ compounds towards oxidation to their +3 state. (ns) and (n -1) d electrons have … Why do transition elements show variable oxidation states? Compound (B) on reaction with KC1 forms an orange coloured crystalline compound (C). (ii) \(\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(\mathrm{aq})\) + I–(aq) +H+(aq) → 2Cr3+ + 7H2O + 3I2. (i) Name the element showing maximum number of oxidation states among the first… The reaction is given as: (ii) Which element shows only +3 oxidation state? Hence basic character of hydroxides also decreases i.e. Hence they have high enthalpies of atomization. 3MnO4-2 + 4H+ → 2MnO4– + MnO2 + 2H2O (i) The transition metals form a large number of interstitial compounds in which small atoms such as hydrogen, carbon, boron and nitrogen occupy the empty spaces in the crystal lattices of transition metals. Thus transition elements exhibit variable oxidation states. For example, the oxidation state of Iron is between 2+ to 6+. However, this variability is less common in metals apart from the transition elements. Transition metals and their compounds are often good catalysts. Answer: (i) Zn is not regarded as a transition element. Absence of unpaired d electrons causes weak metallic bonding. (ii) There is a general increase in density from titanium (Z = 22) to copper (Z = 29). All show oxidation state +2 (except Sc) due to loss of two 4s electrons. (i) Cu+ ion is unstable in aqueous solutions. 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