Chemistry: d-block elements (Transition elements)

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Transition metals

Features: high m.p., high density, good conductors of electricity, rigid and similar atomic radius.

-          Ability to make alloy: similar atomic radius make them able to stay smoothly on the same metallic layer, so their alloy can be strong.

-          Colored ion: Ti³⁺ (purple), Ni²⁺ (green), variable state of V and Mg; this is because their absorbance spectrum appears in the visible light spectrum. White light – absorbed spectrum = color of the ion. For example, Cu²⁺ absorbs the spectrum 650~900nm, leaving the visible light from 400~600nm which is purple, blue and green. So it appears to be blue.

Variable oxidation state

-          Except Sc and Zn, all transition metals in period 4 exist in more than one oxidation state. Ti (+1~+4), V(+2~+5), Cr(+1~+6), Mn(+1~+7), Fe(+1~+6), Co(+1~+5), Ni(+1~+5), CU(+1~+3), Sc, Ti, V, Cr appears commonly in +3 while the rest also exist commonly in +2.

-          Lower oxidation states are usually found in simple ions or ionic compound, like Cr³⁺, FeO. Higher oxidation states exist with covalent bonding with highly electronegative atoms like O and Cl, e.g. VO₃^-, CrO₄^2-.

Catalytic properties of transition metal, e.g., Fe in Haber process, V₂O₅ in contact process, Pt-Rh (Rhodium) in producing ammonia, Ziegler-Natta Catalyst (Et₃Al/TiCl₄) in producing PE, Ni in hydrogenation and CuO in oxidation of ethanol to ethanal.

It’s also used as tracers like ⁶⁰Co (radioactive) and nutrition like Co in Vitamin B₁₂.

Vanadium usually it exist in 4 oxidation state: +5(yellow, dioxovanadium(V) ion VO₂⁺), +4(blue, oxovanadium(IV) ion VO²⁺), +3(green, vanadium(III) ion V³⁺) and +2(purple, vanadium(II) V²⁺), starting from ammonium metavanadate NH₄VO₃ solution (red solution initially and turn yellow later), VO₂⁺ is produced. Since in ECS the reaction between Zn and Zn²⁺ is above the reduction of VO₂⁺, VO²⁺, V³⁺, so under finely powdered Zn and H₂SO₄ as catalyst, it reduces VO₂⁺ all the way to V²⁺. It can’t reduce V²⁺ to V because this is higher than Zn in the ECS.

Manganese usually exist in 5 oxidation state: +7(MnO₄-), +6(permanganate, dark green, in alkaline only, MnO₄^2-), +4(MnO₂, black solid), +3(Mn(OH)₃, brown solution) and +2(Mn²⁺). It’s an useful oxidizing agent with dilute H₂SO₄. In alkaline condition permanganate change to MnO₂ by MnO₄^- + 2H₂O + 3e^- → MnO₂ + 4OH^-.

Iron usually exists in oxidation state of +2 and +3, Fe²⁺ act as both oxidizing and reducing agents.

Note: Sc and Zn are usually regarded as non-typical transition metal because their ion is colourless and they only have one oxidation state.