15: Transition Metals
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What are transition metals?
D-block elements that form stable ions with partially-filled d-orbitals
Why isn’t scandium considered a transition metals?
Its common ion (Sc3+) doesn’t have a partially filled d-orbital (no electrons in the d orbital)
Why isn’t zinc considered a transition metals?
Its common ion (Zn2+) doesn’t have a partially filled d-orbital (full d-orbital)
Why do transition metals have variable oxidation states?
The small energy gap between 4s and 3d orbitals means different numbers of electrons can be readily lost
What makes transition metals make useful reagents and catalysts?
They have multiple oxidation states
What is a ligand?
A molecule or ion that donates a lone pair to form a coordinate bond with a metal ion
How are complex ions formed?
When a metal ion is surrounded by ligands via coordinate bonds (dative covalent) bonds
What happens the the d-orbital when a ligand bonds to a metal ion?
The ions d-orbitals split into two energy levels (higher and lower)
Why do d-orbitals split into two energy levels when the ion forms a bond with a ligand?
This occurs because electrons in the d-orbital are repelled by electrons from incoming ligands
What causes an energy gap to form between orbitals?
Different d-orbital shapes experience differing amounts of repulsion
What causes the colour of transition metals as ions?
Electrons can absorb energy from visible to move from a lower energy level (ground state) to a higher one (excited state) The remaining wavelengths of light are transmitted or reflected, giving the solution its observed colour
When can a colour change occur?
1) The oxidation state of the metal changes 2) The ligand changes 3) The coordination number changes No colour is seen if the metal has a full or empty d-orbital , so no electron transitions can occur
What is the co-ordination number?
The number of co-ordinate bonds around a central metal ion and determines the shape of the complex
What is the shape of a complex ion with 6 ligands? How would you draw it?
Octahedral 2 normal dative bond lines (above and below, straight line) 2 dative bond lines away from the paper (dotted lines) 2 dative bond lines towards the paper (wedged line)
What is the shape of a complex ion with 4 ligands?
Tetrahedral (often with larger ligands) or square planar
What are the properties of transition metals?
● Hard solids ● Catalytic property ● High melting point and boiling point ● Coloured ions and compounds ● Ions with different oxidation numbers ● Ions with incompletely-filled d-orbitals
What enables the metal ion to be more strongly attracted to the ligands?
The increase in charge density (smaller ion/higher charge)
How do you calculate charge density?
Charge density = charge / volume
How do you name complex ions?
1) Number of the ligand (di- , tri- , tetra) followed by the name of the ligand 2) Ligands are written in alphabetical order (aqua- before chloro-) 3) Name of metal (if the overall charge is negative then the metal will end in -ate) 4) Oxidation state of metal ion Example: Tetraaquadichlorochromium (III)
What determines the colour on transition metal ions?
The electrons on the 3d orbitals
How does colour depend on electrons in 3d orbitals?
1) The energy level splits into two levels 2) Electron from lower energy level is excited to higher energy level by absorbing the certain amount of energy between these two energy levels 3) Remainder of visible light reflected is the colour of the compound observed
How do you know when a complex ion with four ligands has a tetrahedral or square planar shape?
They usually are tetrahedral but are sometimes square planar - complex ions containing nickel, platinum and palladium tend to be square planar
How would you draw a square planar?
Two dotted lines at the top (away from the paper) Two wedged lines at the bottom (towards the paper)
How would you draw a tetrahedral?
Two normal lines One wedged line One dotted line