Chapter 24 - Transition Elements

What is a transition element?

• d-block elements that form at least one ion with a partially filled d-orbital

Why are scandium and zinc not classed as transition elements?

• scandium only forms the ion Sc³⁺

  • loses two 4s electrons and 1 3d electron

  • ion has no electrons in the 3d subshell

• zinc only forms the Zn²⁺ ion

  • loses two 4s electrons

  • has a full 3d subshell

What are properties of the transition metals?

• form compounds in which the transition element can have different oxidation states

• form coloured compounds

• can act as catalysts

What are examples of when transition metals are used as catalysts?

• haber process

  • manufacture of ammonia

  • catalysed by an iron catalyst

• contact process

  • production of sulfur trioxide from the oxidation of sulfur dioxide

  • catalysed by vanadium (V) oxide, V₂O₅

• hydrogenation of vegetable fats in manufacture of margarine

  • nickel catalyst

What is a ligand?

• a molecule or ion that donates a pair of electrons to a central metal ion to form a dative covalent bond

What is the coordination number?

• indicates the number of coordinate bonds attached to the central metal ion

What are monodentate ligands?

• a ligand that is able to donate one pair of electrons to a central metal ion

• e.g.

  • water (H₂O)

  • ammonia (NH₃)

  • chloride (Cl^-)

  • cyanide (CN^-)

  • hydroxide (OH^-)

What are bidentate ligands?

• can donate two lone pairs of electrons to a central metal ion

• forms 2 coordinate bonds

• e.g.

  • 1,2-diaminoethane (EN) (NH₂CH₂CH₂NH₂)

  • ethanedioate (oxalate ion) (C₂O₄^2-)

What transition metals form square planar complexes?

• complex ions of transition metals with 8 d-electrons in the highest energy d subshell

• platinum (II), palladium (II) and gold (II)

What is a ligand substitution?

• one ligand in a complex ion is replaced by another ligand