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D-BLOCK, , ?, A LOT OF COMMERCIAL AND IMPORTANT, METALS THAT WE USE LIKE IRON(FE), ©, GOLD(AU), SILVER(AG), COPPER(CU) ETC ARE, TRANSITION ELEMENTS. C, , AS ALL TRANSITION ELEMENTS ARE, ESSENTIALLY METALS, THEY ARE ALSO, CALLED TRANSITION METALS. ©, , DEFINITION : Initially they were named “transition", , elements because their properties were found to be, transitional between s & p block elements., , However, IUPAC definition is as follows,, , Transition metals are metals which have incomplete CBSE e015, d subshell either in neutral atom or in their ions., , Thus, elements which have one or more unpaired d, , electrons in their ground state or in their common, , oxidation state can be called transition elements., , , , A lot of elements do not possess unpaired electrons in their ground state, but this definition helps identify them as transition elements., Eg- Copper (Cu) CBSE 2017(2), Cu ‘s Electronic configuration is : 1s#2s*2p®3s*3p®4s'3d'°, As we can see, it has a completely filled d orbital in its ground state, but in its common Oxidation State i.e., +2,, Cu+2 ‘s Electronic configuration is : 1s72s?2p°3s78pt4s°3q9, and it has an unpaired electron thus it can be called a transition, element. A similar case is observed for Silver. PBS 207, , The possession of unpaired d and f electrons makes transition elements, different from s & p block elements and hence there study is carried out, separately.

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IME IMPORTANT DEFINITIONS AN ONCEP, , These concepts would appear later in the chapter a lot so they should be, , understood before hand., , , , ENT 1ALP OF ATOMISATIO? iat, It is the change in enthalpy when one mole of bonds is completely broken, to obtain atoms in the gas phase., It signifies the inter-atomic strength that the molecules of a compound, possess., Lower AHat——> weaker bonds —-+ easier to break them., Melting Point, Boiling Point etc. depend hugely on AHat as they, essentially are meant to weaken the inter-atomic attraction., , , , It is a type of chemical bond formed between positively charged atoms in, which the free electrons are shared among a lattice of cations. Strength, of metallic bond depends on the size, the charge and the number of de, localisable (unpaired and not in a stable configuration) electrons that the, metal has. Extent of metallic bond hugely influences AH,,. CBSE 2017, , , , , ly 1g, } |, , It is defined as the reduction in the effective nuclear charge on the, electron cloud, due to a difference in the attractive forces of the, , electrons on the nucleus. It is a very important phenomenon used in, explaining atomic size variation in transition metals. As d-orbitals exhibit, bad shielding effect to the outermost s-orbital, the outermost orbital, , experiences a stronger nuclear attraction, hence the size of atom, decreases., , , , The more than expected decrease in size of the lanthanoid series (from, Lanthanum to Lutherium), due to the poor screening effect subjected on, the outermost electrons by the f-subshell.

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In electrochemistry, standard electrode potential is defined as the measure, of the individual potential of a reversible electrode at standard state with, ions at an effective concentration of 1mol dm7? at the pressure of 1 atm., Basically, it is the tendency of an ion to become a neutral atom in aqueous, medium. Negative E° value reflects the fact that the reversible process, which we are studying is not feasible., , E° is heavily affected by these properties and for a more negative E”:, , (i) Lower Enthalpy of Atomisation is required, , (ii) Lower lonisation Enthalpy is required, , (iii) Higher Hydration Enthalpy is required, , , , IUPAC gives several different definitions of oxidation: loss of electron,, increase in positive valuc of oxidation state, decrease in negative value of, oxidation state, loss of hydrogen, or gain of oxygen., , So, gain of electron, decrease in positive value of oxidation state, increase, , in negative value of oxidation state, gain of hydrogen, or loss of oxygen are, the various definitions of recicuat,, , , , -The general outer Nekectnénie Ponsetnation of transition metals is (n1)d'-1°ns!-2,, -Although a lot of exceptionsvarise to this “formula” because there is very, little energy difference between the ns and (n-1)d orbitals .., Eg — Copper(Cu) and Chromium(Cr):, -The element just before Cr is Vanadium(V)-28 and its electronic, configurationis, 1s?2s?2p°3s?3p°4s?3d$, So according to Aufbau principle, Cr’s electronic configuration, should be, 1822s22:p°3s23p%4s23d4 ,but the actually found, configuration is 1s22s522p%3s23p%4s13d8., -This is because this configuration has a half filled d orbital which, is very stable., -A similar anomaly is found for Cu., Nickel(Ni)-28, which is just before Cu, has the electronic, configuration, 1s22s22p®3s28p%4s23d8,, -So the configuration of Cu should be, 1s22s?2p®3s?3p%4s23d9,, but the actual configuration is, 1s22s22p®3s23p%4s!3d10., -This is because there is a fully filled d orbital in this configuration, which is highly stable.