Revise: Transition Elements
The 3d series transition elements, the electron configurations behind their variable oxidation states and coloured compounds, and their everyday uses.
A transition element forms at least one ion with a PARTIALLY filled d subshell.
Zn²⁺ (full 3d¹⁰) is a borderline exception — colourless, only one oxidation state.
Both 4s and some 3d electrons are accessible, giving multiple oxidation states.
Mn in KMnO₄ has oxidation state +7.
Colour comes from electrons jumping between split d orbital energy levels.
Cu²⁺ solution appears blue.
Iron/steel (strength), copper (conductivity), titanium (implants), Pt/Pd (catalysts).
Titanium hip replacements resist corrosion in the body.
The 3d series fills 3d after 4s, with Cr and Cu as key exceptions.
Cr: [Ar]3d⁵4s¹ (half-filled 3d is extra stable).
Partially filled d orbitals cause variable oxidation states and colour.
Sc³⁺ (empty 3d) is also a borderline exception.
Balance oxidation states so the total equals the compound/ion charge.
Cr in K₂Cr₂O₇ has oxidation state +6.
Ions with empty or full d subshells (Sc³⁺, Zn²⁺) are typically colourless.
Pt/Pd catalyse exhaust reactions by cycling oxidation states.
Every use traces back to a specific property covered in this chapter.
Copper's delocalized electrons make it an excellent conductor.