Write about the coloured ions formation of actinoids.

(i) Elements having incomplete d-orbitals in their atoms or in their simple ions.

(ii) Four series of transition metals: The series involving filling of $3\mathrm{d}-, 4\mathrm{d}-, 5\mathrm{d}- \mathrm{and} 6\mathrm{d}-$ subshell respectively.

(iii) All transition elements are metals. They possess characteristic properties of metals such as high tensile strength, malleability, ductility and thermal and electrical conductivity.

(iv) Transition elements have high melting and boiling points due to stronger interatomic bonding.

(v) The atomic and ionic radii of transition elements are smaller than those of $\mathrm{s}-$block elements but larger than those of $\mathrm{p}-$block elements.

(vi) Transition elements exhibit higher enthalpies of atomisation due to stronger interatomic bonding.

(vii) Among the elements of the first transition series, zinc has the least enthalpy of atomisation.

(viii) In the $3\mathrm{d}-$ transition series, $\mathrm{Cu}$ is the only element which has positive electrode potential for the ${\mathrm{M}}^{2+}/\mathrm{M}$ couple.

(ix) Transition elements exhibit variable oxidation states due to participation of $(\mathrm{n}-1)\mathrm{d}$electrons in bonding.

(x) Among the elements of the $3\mathrm{d}-$transition series scandium does not show variable oxidation states while manganese shows maximum number of oxidation states.

(xi) The most common oxidation state of the elements of the first transition series is $+2$.

(xii) Transition elements form coloured complexes. Colour of the complexes is due to absorption of light energy due to d-d transitions in partially filled d-orbitals.

(xiii) Most of the transition element compounds are paramagnetic due to the presence of unpaired electrons in them. The magnetic moment is due to orbital motion and spin of the unpaired electrons. The ‘spin only’ magnetic moment is given by the relation: $\mathrm{\mu }=\mathrm{n}(\mathrm{n}+2) \mathrm{BM}$ .

(xiv) Zinc, cadmium and mercury do not show characteristic properties of transition elements because they do not contain partially filled d-orbitals in their atoms or common oxidation states.

2. Oxides of transition metals:

(i) The first series transition metal oxides are generally formed by the reaction of metals with oxygen at high temperatures. These oxides may be acidic, basic or amphoteric. These oxides dissolve in acids and bases to form oxometallic salts. ${\mathrm{K}}_2{\mathrm{CrO}}_4,{\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7 \mathrm{and} {\mathrm{KMnO}}_4$ are common examples of oxometallic salts.

(ii) Potassium dichromate is prepared from chromite ore $\left({\mathrm{FeCr}}_2{\mathrm{O}}_4\right)$ by fusion with alkali in the presence of air and acidifying the extract.

(iii) Potassium Permanganate is prepared from pyrolusite ore $\left({\mathrm{MnO}}_2\right)$.

(iv) Both potassium dichromate and potassium permanganate are strong oxidising agents.

(v) Chromate ${{\mathrm{CrO}}_4}^{2-}$, permanganate ${\mathrm{MnO}}^{4-}$ and manganate ${{\mathrm{MnO}}_4}^{2-}$ ions have tetrahedral geometry.

(vi) Dichromate ion ${\mathrm{Cr}}_2{{\mathrm{O}}_7}^{2-}$ consists of two tetrahedra sharing one comer with $\mathrm{Cr}-\mathrm{O}-\mathrm{Cr}$ bond angle of $126°$

3. Inner Transition Elements(f- block elements):

(i) Elements in which the last electrons enter the f-subshell of antepenultimate energy level.

(ii) Lanthanides are a series of elements which involve filling of $4\mathrm{f}-$ subshell. These are fourteen elements following lanthanum from Cerium to Lutetium.

(iii) Actinides are a series of elements which involve filling of $5\mathrm{f}-$ subshell. These are fourteen elements following Actinium from Thorium to Lawrencium.

(iv) Lanthanoid Contraction: The steady decrease in size of lanthanoid ions ${\mathrm{M}}^{3+}$ with increase in atomic number.

Lanthanum and all the lanthanoids are rather soft white metals. They react easily with water to give solutions giving $+3$ ions.

(v) The common oxidation state of lanthanoids and actinoids is $+3$.