Transition Metals - Topic 15 Flashcards
Characteristics of transition metals
•complex formation,
•formation of coloured ions,
•variable oxidation state
•catalytic activity.
Why is Zn not a transition metal
Zn can only form a +2 ion. In this ion the Zn2+ has a complete d orbital and so does
not meet the criteria of having an incomplete d orbital in one of its compounds.
Why is Sc not a transition metal?
Sc can only form a +3 ion. In this ion the Sc3+ has an empty d orbital and so
does not meet the criteria of having an incomplete d orbital in one of its ions.
Describe the trend in ionisation energy for elements Sc to Zn
The successive ionization energies for the elements Sc to Zn show a gradual increase in ionisation
energy until all the 4s and 3d electrons have been removed. There is then a big jump as electrons start
to be removed from the inner core electrons
What is coordinate bonding
the shared pair of electrons in the covalent bond
come from only one of the bonding atoms.
What is a complex
a central metal ion surrounded by ligands
What is a ligand
An atom, ion or molecule which can donate a lone electron pair
monodentate
Where ligands can form one coordinate bond per ligand
Bidentate
Ligands can have two atoms with lone pairs
and can form two coordinate bonds per ligand
Multidentate
Ligands can have more than two atoms with lone pairs
and can form more than two coordinate bonds per ligand
Draw EDTA
Page 1 Chemrevise
What cause colour change in transition metals
- oxidation state,
- co-ordination number
- ligand
How does colour arise in transition metals
- Colour arises from electronic transitions from the ground state to excited states: between different d
orbitals - A portion of visible light is absorbed to promote d electrons to higher energy levels. The light that is not
absorbed is transmitted or reflected to give the substance a complementary colour.
How is the colour of a transition metal changed
Changing a ligand or its shape, changing the coordination number or changing the oxidation state of a metal ion will alter the energy split between the d- orbitals, changing delta E and hence change the frequency of light absorbed.
Why does Sc3+ not have colour
As it hasn’t got any d electrons left to move around. So there is not an energy transfer equal to that of visible light
Why doesn’t Zn2+ and Cu+ not have any colours
Zn2+ ions and Cu+ ions the d shell is full
e.g.3d10 so there is no space for electrons to transfer. So there is not an energy transfer equal to that of visible light
What is Spectrophotometry used for in transition metal complexes
It is used to determine the concentration of coloured ions by measuring their absorption of visible light
How does Spectrophotometry work
1) light at increasing frequency is passed through a sample of a coloured complex ion
2) some light is absorbed
3) the amount of light absorbed is proportional to the ion concentration
4) a ligand may be added to intensify colour of complexes with pale colour and that do not absorb light strongly
What steps are involved in using Spectrophotometry to determine ion concentration
1) add appropriate ligand to intensify colour
2) Make up solutions of known concentration
3) Measure absorption or transmission
4) Plot graph of results or calibration curve
5) Measure absorption of unknown and compare
Shapes of complex ions
- octahedral (usually with complexes with small ligands e.g NH3 and H2O)
- tetrahedral (usually with complexes with larger ligands e.g Cl-)
- square planar
- linear (usually just Ag+)
Draw structure of cisplatin
Pg 3 chem revise
What is cisplatin used for
An anticancer drug
How does cisplatin act as an anticancer drug
- the two chloride ions are displaced and the molecule joins on to the DNA of cancer cells by dative and hydrogen bonding. In doing this it stops the replication of cancerous cells.
- It prevents the replication of healthy cells by bonding on to healthy DNA which may lead to unwanted side effects like hair loss
What happens to cisplatin in the body
One chloride ligand is substituted by a water molecule
Pt(NH3 )2Cl2 + H2O -> [Pt(NH3)2Cl(H2O)]+ + Cl–