Transition Metals

• A transition metal is a metal that can form one or more stable ions with a partially filled d subshell.
• A ligand is a molecule that forms a coordinate/dative covalent bond with a transition metal/ion. A lone pair of electrons is donated to the metal ion.
• An ion with ligands attached to it is called a complex ion
• The coordination number of an ion is defined as the number of dative bonds made with the central metal ion
• • A ligand that can form two bonds is called bidentate.
  • A ligand that can form one bond is called monodentate.
  • A ligand that can form multiple bonds is called multidentate.
• • Multidentate ligands will almost always replace monodentate ligands at a metal centre. This is called the chelate effect.
  • The chelate effect is based on entropy.
  • When you substitute a multidentate ligand for a monodentate ligand, you increase the number of moles of molecules in the products of the reaction.
  • This leads to a large increase in entropy, meaning the reaction is favoured
• In the presence of ligands, d orbitals will split. Some of them gain energy, and some of them lose energy.
• Electrons will occupy the lower energy orbitals first.

  If an electron absorbs energy equal to the energy gap between orbitals, it can move to occupy the higher energy orbitals. This is called an excited electronic state.

  Electrons will absorb frequencies of light that contain enough energy to jump the energy gap.
• When a transition metal ion is in light, it will absorb the frequencies which correspond to the d sub-shell energy gap.

  
  

  The rest of the frequencies will be reflected.

  
  

  You only see the reflected light
• $[Fe(H_2O)_6]^{2+}$ (a green solution) reacts with the following aqueous solutions:

  
  

  $NaOH$: Green ppt. of $Fe(OH)_2(H_2O)_4$ is formed, which doesn't dissolve in excess NaOH

  
  

  $NH_3$: Green ppt. of $Fe(OH)_2(H_2O)_4$ is formed, which doesn't dissolve in excess NH3

  
  

  $Na_2CO_3$: green ppt. of $FeCO_3$is formed
• $[Cu(H_2O)_6]^{2+}$ (a blue solution) reacts with the following aqueous solutions:

  
  

  $NaOH$: Blue ppt. of $Cu(OH)_2(H_2O)_4$ is fformed, with no change in excess

  
  

  $NH_3$: Blue ppt. of $Cu(OH)_2(H_2O)_4$ is formed. In excess NH3, a deep blue solution of $[Cu(NH_3)_4(H_2O)_2]^{2+}$ is formed

  
  

  $Na_2CO_3$: ppt of $CuCO_3$, green-blue
• $[Al(H_2O)_6]^{3+}$(a colourless solution) reacts with the following aqueous solutions:

  
  

  $NaOH$: white ppt of $Al(OH)_3(H_2O)_3$, in excess NaOH $[Al(OH)_4]^-$ is formed

  
  

  $NH_3$: $Al(OH)_3(H_2O)_3$ (white ppt) is formed, with no change in excess

  
  

  $Na_2CO_3$: $Al(OH)_3(H_2O)_3$ (white ppt) is formed
• $[Fe(H_2O)_6]^{3+}$ (yellow solution) reacts with the following aqueous solutions:

  
  

  $NaOH$: $Fe(OH)_3(H_2O)_3$ (brown ppt), with no change in excess

  
  

  $NH_3$:$Fe(OH)_3(H_2O)_3$ (brown ppt), with no change in excess.

  
  

  $Na_2CO_3$: brown ppt of $Fe(OH)_3(H_2O)_3$ formed.
• The compounds of vanadium, with colours and oxidation states:

  • $V: 0$
  • $V^{2+} : +$$2, violet$
  • $V^{3+} : +$$3, green$
  • $VO^{2+}: +$$4, blue$
  • $VO_2^{+} : +$$5, yellow$
• The reductions of vanadium(V) to vanadium (II) are below:

  
  

  ${2VO_2^{+}}_{(aq)} +$$Zn_{(s)} +$${4H^+}_{(aq)} \rightarrow {2VO^{2+}}_{(aq)} +$${Zn^{2+}}_{(aq)} +$${2H_2O}_{(aq)}$

  
  

  ${2VO_2^{+}}_{(aq)} +$$Zn_{(s)} +$${4H^+}_{(aq)} \rightarrow {2VO^{2+}}_{(aq)} +$${Zn^{2+}}_{(aq)} +$${2H_2O}_{(aq)}$${2V^{3+}}_{(aq)} +$$Zn_{(s)} \rightarrow {2V^{2+}}_{(aq)} +$${Zn^{2+}}_{(aq)}$