A-level Chemistry: 3.2.5 Transition Metals Part 1

d-block

A metal that can form one or more stable ions with a partially filled d sub-level

(d-orbital can contain up to 10 electrons)

All period 4 d-block elements are transition metals expect scandium and zinc

Incomplete d sub-level

• Scandium only forms one ion, Sc3+, which has empty d sub-level
  

  • Sc = [Ar] 3d1 4s2

  • When loses 3 electrons to form Sc3+

  • Ends up with electron configuration [Ar]

• Zinc only forms one ion, Zn2+, which has full d sub-level
  

  • Zn = [Ar] 3d10 4s2

  • Forms Zn2+ = loses 2 electrons both from 4s sub-level

  • ∴ keeps full 3d sub-level

positive

s electrons removed first & then d electrons

• Form complex ions

• Form coloured ions

• Good catalysts

• Exists in variable oxidation states

• ∵ energy levels of 4s and 3d sub-levels are very close to one another

• ∴ different no. of electrons can be gained or lost using fairly similar amounts of energy

Purple

orange

yellow

blue

green

violet/green

purple/yellow

Violet

Pale pink

Pale green

Pink

green

blue

A complex is a central metal atom or ion surrounded by co-ordinately bonded ligands

Covalent bond in which both electrons in the shared part come from the same atom

(In complex, they come from ligand)

Atom, ion or molecule that donates a pair of electrons to a central transition metal ion to form a co-ordinate bond

no. of co-ordinate bonds that are formed with the central metal ion

H2O or NH3

6

Cl-

4

6 co-ordinate bonds mean an octahedral shape

90°

[Co(NH3)6]3+ (aq)

4 co-ordinate bonds usually mean a tetrahedral shape

109.5°

4 co-ordinate bonds can form a square planar shape

e.g. cisplatin

90°

Some silver complexes have 2 co-ordinate bonds and form a linear shape

180°

total oxidation state

Determine the charge on the metal ion by balancing the overall charge of the compound using known oxidation states of other atoms.

+2

+3

∵ otherwise it won't have anything to use to form a co-ordinate bond

Ligands that only form 1 co-ordinate bond

Ligands that form more than 1 co-ordinate bond

e.g. EDTA4- has 6 lone pairs

• (multidentate) ligands that can form 2 co-ordinate bonds

• Donates an electron pair from two different atoms

Haemoglobin contains Fe2+ ions, which are hexa-coordinated (6 co-ordinate bonds) = octahedral structure

• Haem is an iron(II) complex with a multidentate ligand

  • 4 co-ordinate bonds come from single multidenate ligand

  • 4 nitrogen atoms from same molecule co-ordinate around Fe2+ to form circle

  • This part of molecule is called haem

Other 2 co-ordinate bonds come from protein called globin, and oxygen or water molecule

Complex can transport oxygen to where its needed & then swap it for a water molecule

1. In lungs (O₂ = high), O₂ substitutes water ligand and bonds co-ordinately to Fe(II) ion to form oxyhaemoglobin which is carried around the body in the blood

2. When oxyhaemoglobin gets to place where O₂ is needed, oxygen molecule is exchanged for water molecule

1. Haemoglobin swaps its water ligand for a CO ligand forming carboxyhaemoglobin

2. CO = strong ligand & doesn't readily exchange with oxygen or water ligands ∴ haemoglobin can't transport oxygen

optical isomerism (type of stereoisomerism)

Where ion can exist in 2 forms that are non-superimposable mirror images

Happens with octahedral complexes when 3 bidentate ligands (e.g. ethane-1,2-diamine) co-ordinately bond with central metal ion (e.g. nickel)

Cis-Trans Isomers can form in Octahedral and Square Planar Complexes

Octahedral complexes with 4 monodentate ligands of 1 type & 2 monodentate ligands of another type

If 2 odd ligands are opposite each other

If 2 odd ligands are next to each other

Square planar complex ions that have 2 pairs of ligands

Some of the orbitals gain energy which splits the 3d orbitals into 2 different energy levels

lower orbitals/ground state

• They need energy equal to the energy gap, ΔE

• Get this energy from visible light

• Central metal ion

• Its oxidation state

• Ligands

• Co-ordination number

The larger the energy gap, the higher the frequency of light that is absorbed

1. When visible light hits transition metal ion, some frequencies are absorbed when d electrons jump to higher orbitals/are excited

   • Frequencies absorbed depend on size of energy gap (ΔE)

2. Rest of frequencies transmitted or reflected

3. These frequencies combine to make complementary colour of the absorbed frequencies = colour you see

4. e.g. hydrated [Cu(H2O)6]2+ ions

   1. Absorb "red" light

   2. Rest of frequencies combine to produce complementary colour = blue

• If no 3d electron or 3d sub-level is full

• = no electron will jump ∴ no energy absorbed

• ∴ compound = white/colourless

By any factors that can affect the size of the energy gap (ΔE)

The conc. of a solution by measuring how much light it absorbs

1. White light shone through filter, that only lets through the colour of light that's absorbed by the sample

2. Light passes through sample to colorimeter

   • Calculates how much light was absorbed by the sample

3. More conc. coloured solution is = more light it'll absorb

• Produce a calibration curve

  • Involves measuring absorbance of known conc. of solutions & plotting results on a graph

• Then can measure absorbance of your sample & read its conc. off the graph

If ligands are of similar size and the same charge, then the co-ordination number and shape of the complex ion doesn't change

If ligands are different sizes, they'll be a change in co ordination number and shape