10.3. Chemistry of Scandium Sc, Z=21, 1s²2s²2p⁶3s²3p⁶3d¹4s²

data comparison of scandium with the other members of the 3d–block and transition metals

Elect. pot. = standard electrode potential data for scandium (E^Ø at 298K/25^oC, 101kPa/1 atm.)

na = data not applicable to scandium

Extended data table for SCANDIUM

• Uses of SCANDIUM

  • Scandium is a silvery–white metal and not a particularly important element but does have some uses.

  • Scandium oxide, Sc₂O₃, is used in electronic components.

  • Scandium iodide, ScI₃, is used in high intensity light–bulbs.

  • Scandium carbide, ScC, is a hardening agent for titanium carbide, making it the second hardest substance known.

• The colour of scandium compounds

  • Most scandium compounds and complex ions (Sc only exhibits a +3 oxidation state in them) are white or colourless.

    • The lack of scope for a variety of coloured compounds arises from the fundamental electronic configuration of the Sc³⁺ ion, namely [Ar]3d⁰, giving a completely empty 3d sub–shell.

      • ie there is no electron that can be promoted to a higher level when the 3d sub–shell is split when the central metal ion interacts with the ligands.

      • 

      • Top left shows the ground state of the scandium(III) ion, and the possible 3d orbital splitting, and clearly, no 3d electron can be promoted, so no absorption of visible light photons, all visible light transmitted, so no colour!

      • Even though scandium is a member of the 3d block of elements, this is why scandium is NOT a true member of the first transition metal series, it forms no ion with a partly filled 3d sub–shell.

      • For more details see Appendix 4. Electron configuration & complex ion colour theory

The Chemistry of SCANDIUM

The oxidation state and electron configuration of scandium in the context of the 3d block of elements

• The electrode potential chart highlights the value for the one positive oxidation state of scandium.

• Scandium is quite an electropositive metal and will dissolve in acids liberating hydrogen.

  • As you can see from the electrode potential chart above ...

  • Sc³⁺_(aq)  +  3e^-    Sc^(s)   E^θ = -2.03 V

• Scandium's chemistry is entirely based on the +3 oxidation state (Sc³⁺), the result of losing the outer 3d and 4s electrons.

• So it forms a typical series of binary compounds with non–metals e.g. Sc₂O₃,  ScCl₃ etc.

• Scandium dissolves in acids to form salts e.g. scandium chloride from hydrochloric acid.

  • 2Sc(s) + 6HCl(aq) ===> 2ScCl₃(aq) + 3H₂(g)

  • Note that the Roman numerals (III) are NOT needed in the name, since only one oxidation state is possible for scandium and you would be expected to know that.

• With oxygen scandium forms a white basic oxide, scandium oxide Sc₂O₃,

  • 2Sc(s) + 3O₂(g) ===> Sc₂O₃(s)

  • which dissolves in acids to form colourless solutions of the respective salt e.g.

  •  Sc₂O₃(s) + 6HCl(aq) ===> 2ScCl₃(aq) + 3H₂O(l)   (scandium chloride)

  •  Sc₂O₃(s) + 3H₂SO₄(aq) ===> Sc₂(SO₄)₃(aq) + 3H₂O(l)   (scandium sulfate)

  •  Sc₂O₃(s) + 6HNO₃(aq) ===> 2Sc(NO₃)₃(aq) + 3H₂O(l)   (scandium nitrate)

• The scandium(III) ion, Sc³⁺ ion, [Sc(H₂O)₆)]³⁺ has an empty sub–shell, 3d⁰, which does not allow the electronic transitions which account for the colour in transition metal compounds.

  • 

  • In the scandium(III) ion, no 3d electronic transitions are possible to absorb regions of visible light and produce a colour from transmitted light colours not absorbed.

  • See Appendix 4. for more on complex ion colour theory

• The aqueous octahedral hexaaqua ion of scandium, [Sc(H₂O)₆]³⁺ is therefore colourless (shown as grey in the diagram!) and with no other oxidation state possible i.e. no ion with an incomplete 3d sub–shell with at least one electron, although a member of the 3d–block, scandium is NOT a true transition metal.

  • The hexa-aqua ion of scandium is a typical octahedral complex.

  • Apart from the colourless Sc³⁺ and Zn²⁺ all the other M²⁺ or M³⁺ hexaaqua ions of the 3d block are coloured.

• With alkali, the aqueous scandium ion Sc³⁺ forms a white gelatinous precipitate of hydrated scandium hydroxide, Sc(OH)₃,

  • Sc³⁺(aq) + 3OH^–(aq) ==> Sc(OH)₃(s)

    • A simplified formula for the neutral hydroxide complex is [Sc(OH)₃(H₂O)₃]⁰

  • Scandium hydroxide is a basic hydroxide and not amphoteric i.e. it does not dissolve in excess alkali, but scandium hydroxide readily dissolves in acids to form salts e.g. to form scandium chloride, scandium nitrate or scandium sulfate ...

  • Sc(OH)_3(s) + 3HCl_(aq) ===> ScCl_3(aq) + 3H₂O_(l)

  • Sc(OH)_3(s) + 3HNO_3(aq) ===> Sc(NO₃)_3(aq) + 3H₂O_(l)

  • 2Sc(OH)_3(s) + 3H₂SO_4(aq) ===> Sc₂(SO₄)_3(aq) + 6H₂O_(l)

  • The chemistry of scandium is not very colourful or exciting, but scandium is not without its uses!

  • The equations are similar to those for aluminium hydroxide i.e. you can substitute Al for Sc, but not the amphoteric character of aluminium oxide/hydroxide.

• Summary of some complexes–compounds & oxidation state of scandium compared to other 3d–block elements

keywords and phrases: Why are scandium compounds ions complexes colourless? equations for scandium reacting with acids, equations for scandium oxide reacting with strong acids, equations for scandium hydroxide reacting with acids to give scandium(III) salts, ligand substitution displacement balanced equations formula complex ions complexes ligands colours oxidation states: scandium ions Sc(0) Sc(III) Sc(+3) Sc3+ [Sc(H2O)]3+ 2Sc + 6 HCl ==> 2 ScCl3 + 3H2 2Sc + 3O2 ==> Sc2O3 + 6 HCl ==> 2ScCl3 + 3H2O  Sc2O3 + 3 H2SO4 ==> Sc2(SO4)3 + 3H2O Sc2O3 + 6 HNO3 ==> 2Sc(NO3)3 + 3H2O Sc3+ + 3OH– ==> Sc(OH)3 + 3HCl ==> ScCl3 + 3H2O Sc(OH)3 + 3HNO3 ==> Sc(NO3)3 + 3H2O 2Sc(OH)3 + 3H2SO4 ==> Sc2(SO4)3 + 6H2O [Sc(OH)3(H2O)3] oxidation states of scandium, why there are no redox reactions of scandium involving change of oxidation state for more than one ion of scandium, ligand substitution displacement reactions of scandium, balanced equations of scandium chemistry, formula of scandium complex ions, shapes colours of scandium complexes with water and hydroxide ion the position of scandium in the periodic table its reactivity with acids, quite a negative electrode potential half-cell potential

WHAT NEXT? GCSE Level Notes on Transition Metals (for the basics) The chemistry of Scandium * Titanium * Vanadium * Chromium * Manganese The chemistry of Iron * Cobalt * Nickel * Copper * Zinc * Silver & Platinum Introduction 3d–block Transition Metals * Appendix 1. Hydrated salts, acidity of hexa–aqua ions * Appendix 2. Complexes & ligands * Appendix 3. Complexes and isomerism * Appendix 4. Electron configuration & colour theory * Appendix 5. Redox equations, feasibility, Eø * Appendix 6. Catalysis * Appendix 7. Redox equations * Appendix 8. Stability Constants and entropy changes * Appendix 9. Colorimetric analysis and complex ion formula * Appendix 10 3d block – extended data * Appendix 11 Some 3d–block compounds, complexes, oxidation states & electrode potentials * Appendix 12 Hydroxide complex precipitate 'pictures', formulae and equations Some pages have a matching sub-index Advanced Level Inorganic Chemistry Periodic Table Index: Part 1 Periodic Table history Part 2 Electron configurations, spectroscopy, hydrogen spectrum, ionisation energies * Part 3 Period 1 survey H to He * Part 4 Period 2 survey Li to Ne * Part 5 Period 3 survey Na to Ar * Part 6 Period 4 survey K to Kr AND important trends down a group * Part 7 s–block Groups 1/2 Alkali Metals/Alkaline Earth Metals * Part 8  p–block Groups 3/13 to 0/18 * Part 9 Group 7/17 The Halogens * Part 10 3d block elements & Transition Metal Series * Part 11 Group & Series data & periodicity plots All 11 Parts have their own sub-indexes near the top of the pages Group numbering and the modern periodic table The original group numbers of the periodic table ran from group 1 alkali metals to group 0 noble gases (= group 8). To account for the d block elements and their 'vertical' similarities, in the modern periodic table, groups 3 to group 0/8 are numbered 13 to 18. So, the p block elements are referred to as groups 13 to group 18 at a higher academic level, though the group 3 to 0/8 notation is still used, but usually at a lower academic level. The 3d block elements (Sc to Zn) are now considered the head (top) elements of groups 3 to 12.

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