24: Transition Metals

CHAPTER SUMMARY

Transition Metals

• A d-block element that forms one or more stable ions with an incomplete d subshell.

• When forming ions, remove from 4s subshell first.

• Sc is not a transition metal as Sc only forms Sc3+ with electronic configuration [Ar] 4s0 3d0, where the d subshell is empty.

• Zn is not a transition metal as Zn only forms Zn2+ with electronic configuration [Ar] 4s0 3d10, where the d subshell is full.

Orbital Shape

• s: spherical

• p: dumbbell

• d: clover

  • “balloon” in the middle: dxy, dxz, dyz

  • “balloon” in the axis: x2-y2, x2-z2, y2-z2

  • “balloon” in the x and y axes form a clover, which moves around to form a donut shape, dz2

Properties of Transition Metals

1. Variable oxidation states (at least 1 stable ion with incomplete d subshell), since 4s and 3d have similar energy levels

• Mn: [Ar] 4s2 3d5, its maximum oxidation state is 7+ since the next electron would need to be removed from the 3p subshell, which is closer to the nucleus.

• 4s and 3d, 5s and 4d, 6s and 5d have similar energylevels

1. Behave as catalysts

2. Form complex ions

3. Form coloured compounds

4. High melting point

5. High density

6. Hard and rigid

7. Good conductor of electricity and heat

8. 1st IE, atomic radius, and ionic radius do not vary too much across the period

Ligands and Complex Formations

• Fe2+ forms 6 dative bonds

  • Each water molecule donates an electron pair to the Fe atom

  • Octahedral shape (8 faces)

• Ni2+ forms 4 dative bonds with CN-

  • CN- are ligands

  • Square planar

• Co2+ forms 4 dative bonds with Cl-

  • Cl- are ligands

  • Tetrahedral (depends on size)

• Ligands contain a lone pair of electrons that form a dative bond to a central metal atom

• Coordination number: number of coordinate bonds formed by the central atom

• Types of ligands: monodentate (1 dative by a single ligand), bidentate (2 dative), polydentate (more than 2)

The coordinate bonding with ligands causes the orbitals to split into two sets of non-degenerate orbitals.

• Octahedral: Degenerate orbitals separate into two non-degenerate orbitals. The electrons absorb light energy and move to the excited state, absorbing light energy, giving a complementary colour. 3dxy and 3dz2 will experience greater repulsion, pushing the electrons to a higher energy level.

• Tetrahedral: Split into non-degenerate but the repulsion is not as great so it is lifted to an energy level lower than that of octahedral compounds.

Colour Complexes

• Different ligands split the d orbitals by different amounts of energy.

• Different colours are absorbed by visible light so their complementary colours are seen.

• Zn2+ and Sc3+ are colourless

  • Sc3+: No electrons in 3d to absorb light.

  • Zn2+: The orbitals are complete so the electrons cannot go to their excited state.