13.1 First-row d-block elements

• Transition elements are sometimes described as transition metals due to their metallic nature.
• Important: Two exceptions are Chromium and Copper. Cr electron configuration is [Ar]3d⁵4s¹ and not [Ar]3d⁴4s². Cu electron configuration is [Ar]3d¹⁰4s¹ and not [Ar]3d⁹4s².

Characteristics of Transition Elements:

1. Variable oxidation states
   1. Can have oxidation states ranging from +1 to +7
   2. This is due to patterns of successive ionization energies
2. Compounds of transition elements and their ions are often coloured
   1. g. KMnO₄ is purple
   2. g. Cu₂SO₄ . H₂O is blue
   3. Compounds of zinc are colourless unless ligands have chromophore (group of atoms responsible for absorption of electromagnetic radiation)
3. Transition metals form complexes with ligands
   1. Coordinate bonds between metal is bonded to group of atoms/molecules (termed ligands)
   2. See classification of ligands below
4. Transition metals are often used as catalysts
   1. g. (Haber process, biological catalysts)
5. Magnetic properties of transition metals depend on their oxidation states and coordination number
   1. Depend on things such as oxidation state, coordination number, and the geometry of complex.
   2. Paramagnetic contain unpaired electrons that behave as tiny magnetics
   3. Diamagnetic do not contain unpaired electrons and therefore are repelled by external magnetic fields

Classification of Ligands

• Ligands are either negatively charged anions Cl^– or neutral molecules with lone pair (e.g. NH₃)
• Number of coordinate bonds depends on number of lone pairs in ligand which are bonded
• Monodentate ligands are 1 coordinate bond actually bonded. Examples include H₂O and NH₃
• Polydentate (chelate) ligands can form 2 or more. Examples include (EDTA)^4- which can form 6 bonds

Coordination Numbers

• Total number of points of attachment to central element.