• Transition Elements: Metals with ions having a partially filled d-subshell.
  • e.g., chromium(II) ion: 🎨 [Ar] 3d₄
• Transition element cations = Lewis acids. Why? 'Cause they love bonding with Lewis bases!
• Complex Ion: When a transition element ion gets cozy with several Lewis bases.
• Ligands: The surrounding Lewis bases in complex ions.
  • Ligands = Neutral (like H₂O or NH₃) or Anions (like CN−, Cl−, OH−)
  • Ligands are like the back-up dancers for the metal star in the center!
• Electron Role-Play
  • Ligands = Nucleophiles (electron-rich, got lone pairs)
  • Metal cation = Electrophile (positively charged, accepts electron pairs from ligands)
• Complex Ion Party Trick: The charge of the complex ion can be calculated! Here's the magic formula
• Overall Charge of Complex Ion = Charge on transition metal cation + (number of charged ligands x charge on ligand)

Copper's Blue Bath Time 🛁: Imagine dropping a copper(II) ion into a water bath. It doesn't swim alone! It gets surrounded by 6 water molecules forming a blue-colored complex - [Cu(H₂O)₆] 2+ (with an octahedral shape).

• Battle of Cobalt Complex Ions
• Pinky [Co(H₂O)₆] in one corner and Blue [CoCl₄] in another! The former dances with water while the latter prefers chloride ions.
• After some fancy math, we find out the charges
  • [Co(H₂O)₆] = 2+
  • [CoCl₄] = 2−
• Detective Work for Metal Cations
• Complex a: [Fe(OH)(H₂O)5] 2+
  • Metal Cation = Fe₃+
• Complex b: [TiF₆] 2−
  • Metal Cation = Ti₄+