Transition elements

• transition metals are d-block elements that can form at least one ion that has a partially filled d subshell.
• What elements are in the first transition series?

  The elements from titanium to copper.
• Why are copper and chromium exceptions to the Aufbau principle?


  Because an electron from the 4s subshell is promoted to 3d subshell.This makes their electron configurations more energetically stable.
• Transition metals have variable oxidation states, and can form ions with different charges.
• Why do transition metals make good catalysts?


  Because they have variable oxidation states.
• What happens to transition elements during catalysis?


  They change to variable oxidation states by gaining electrons from the reagent and donating electrons to the reagent.
• How can substances be activated using transition elements?

  substances can be absorbed onto the surface of transition metals causing them to be activated.
• A heterogenous catalyst is a catalyst that contains more than one type of active site and it’s in a different state to the reactants.
• What is an example of a transition element that is a heterogenous catalyst?


  The Haber process is catalysed by iron.
• A homogenous catalyst is a catalyst that is in the same state as the reactants. For example, the decomposition of hydrogen peroxide is catalysed by manganese (IV) oxide.
• What are the 4 different properties of transition metals?

  Can behave as catalysts, form coloured compounds, have variable oxidation states, and can form complex ions.
• What is a complex ion?

  Consists of a central metal atom/ion with a number of molecules/ions surrounding it. For example, , [Cr(OH)6]^3-.Chromium is the central metal atom surrounded by 6 OH- ions.The charge of this complex ion is 3-.
• What is a ligand?

  The molecule/ion that forms a dative bond with a transition metal by donating a pair of electrons. In a sense, it acts as a nucleophile.
• Monodentate ligands form only one dative bond to the central transition metal/ion. Water is an example of a monodentate ligand. Bidentate ligands can each form 2 dative bonds to the central transition metal/ion.
• How can bidentate ligands each form 2 dative bonds to the central metal ion?

  They contain 2 atoms that each have a lone pair that can be donated.
• six coordinate complexes can be formed by the bonding of six monodentate ligands/3 bidentate ligands to the central metal ion.
• 4 coordinate complexes can form a tetrahedral shape with a bond angle of 109.5 degrees.

  
• Four coordinate complexes can have a square planar geometry, with a bond angle of 90 degrees.

  
• Cu^2+(aq) can react with 2OH- ions to form Cu(OH)2 and 2H2O. Colour change: blue to pale blue precipitate. When excess NH3 is added to Cu(OH)2, [Cu(NH3)4(H2O)2] +2OH- + 2H2O.
• Cr^3+(aq) can react with 3OH- to form Cr(OH)3/[Cr(OH)3(H2O)3].With excess NaOH, CrOH3 can react to form [Cr(OH)6]^-3.With excess ammonia, Cr(OH)3 can react to form [Cr(NH3)6]^+3.