topic 15A Flashcards
be able to deduce the electronic configurations of atoms and ions of the d-block
elements of period 4 (Sc–Zn), given the atomic number and charge (if any)
Sc 1s22s22p63s23p64s23d1
Ti 1s22s22p63s23p64s23d2
V 1s22s22p63s23p64s23d3
Cr 1s22s22p63s23p64s13d5
Mn 1s22s22p63s23p64s23d5
Fe 1s22s22p63s23p64s23d6
Co 1s22s22p63s23p64s23d7
Ni 1s22s22p63s23p64s23d8
Cu 1s22s22p63s23p64s13d10
Zn 1s22s22p63s23p64s23d10
what are transition metals
- they are d-block elements that form one or more stable ions with incompletely filled d-orbitals
what is a d-block element
the outermost electrons are in a d-subshell
why is zinc not a transition metal
- Zn can only form a +2 ion
- Zn2+ has a complete d orbital hence doesn’t meet the criteria of having an incomplete d orbital in one of its compounds
why is scandium not a transition metal
- Sc can only form a +3 ion
- Sc3+ has an empty d orbital hence doesn’t meet the criteria of having an incomplete d orbital in one of its compounds
trend in ionisation energy in transition metals?
- gradual increase from Sc to Zn until all the 4s and 3d electrons have been removed
- then there is a big jump as electrons start to be removed from the inner core electrons
why do transition metals have variable oxidation states
- transition metals are able to donate and receive electrons and are able to oxidise and reduce
why are transition metals able to oxidise and reduce?
- the ions contain partially filled sub-shells of d electrons that can easily lose or gain electrons
- energy differences between the oxidation states are small
what is a ligand
an atom, ion or molecule which can donate a lone pair of electron
co-ordinate bonding
- when the shared pair of electrons in the covalent bond come from only one of the bonding atoms
- involved in the formation of complex ions
what is a complex ion
a central metal ion surrounded by ligands
what do transition metals form in solution
coloured ions
colour of Cr3+
blue-grey
colour of Mn2+
no colour
colour of Fe2+
pale green
colour of Fe3+
yellow-brown
colour of Ni2+
emerald green
colour of Cu2+
blue
colour of Zn2+
colourless
what do colour changes arise from
- oxidation state
- co-ordination number
- ligand
how does colour arise
- colour arises from electronic transitions from the ground state to excited state between different d-orbitals
- portion of visible light is absorbed to promote d electrons to higher energy levels
- the light that is not absorbed is transmitted to give the substance colour
changing colour - in terms of ligands
- changing a ligand or changing the coordination alters the energy split between the d-orbital
- this changes the energy between the orbitals
- frequency of light being absorbed is hence changed
why do scandium ions have no colour
- Sc is a member of the d block
- Sc3+ has no d electrons left to move around
- there is not an energy transfer equal to that of visible light
- hence no colour
why do zinc ions have no colour
- Zn2+ ions have a full d shell
- hence there is no space for electrons to transfer
- no energy transfer that is equal to that of visible light
- so no colour is seen
why do Cu+ ions have no colour but Cu2+ ions do?
- Cu+ ions have a full d shell so there is no space for electrons to transfer - there is not an energy change equal to that of visible light
- Cu2+ ions have a partially filled d orbital that splits in to two energy levels
spectrophotometry - what is it
- visible light is absorbed to determine the concentration of coloured ions
spectrophotometry - method
- add an appropriate ligand to intensify colour
- make up solutions of known concentration
- measure absorption or transmission
- plot a graph of results/ calibration curve
- measure absorption of unknown and compare
what characteristics do transition metals have
- complex formation
- formation of coloured ions
- variable oxidation state
- catalytic activity
how do colour changes arise
from changes in:
- oxidation state
- co-ordination number
- ligand
- charge on metal ion
- metal
- shape
change in oxidation state
[Fe(H2O)6]3+
[Fe(H2O)6]2+
[Fe(H2O)6]3+ = pale violet
[Fe(H2O)6]2+ = green
change in co-ordination number
[Cu(H2O)6]2+ = blue
[CuCl4]2- = yellow
change in ligand
[Cu(H2O)6]2+ = blue
[Cu(H2O)2(NH3)4]2+ = deep blue
change in metal
[Cu(H2O)6]2+ = blue
[Fe(H2O)6]2+ = green
colour of [Cu(H2O)6]2+
blue
colour of [CuCl4]2-
green
colour of [Co(H2O)6]2+
pink
colour of [Co(NH3)6]2+
yellow
colour of [Co(NH3)6]3+
brown
what is meant by coordination number
the number of coordinate bonds formed to a central metal ion
monodentate ligands
these form one co-ordination bond per ligand
examples of monodentate ligands
H2O:
:OH-
:NH3
what shape are complexes with six-fold coordination
octahedral
why is the shape octahedral
- transition metal complexes form octahedral shapes with small ligands such as H2O and NH3
- bond angle of 90
what shape is formed with slightly larger ligands
tetrahedral
example of larger ligand
Cl-
what other complexes are also formed by transition metals?
square planar
example of square planar
cisplatin
what is cisplatin used as
an anticancer drug
how does cisplatin work
- one chlorine ligand is substituted by a water molecule
- platin binds to DNA of the cancer cells and stops them from dividing
generally, how does cisplatin bind to DNA
via dative covalent bonding and hydrogen bonding
why is cisplatin supplied as a single isomer and not mixed with the trans form
bidentate ligands
- two atoms with lone pairs
- they can form two coordinate bonds per ligand
e.g. of bidentate ligand
NH2CH2CH2NH2
multidentate ligands
- can form six coordinate bonds per ligand
e.g. multidentate ligand
EDTA4-
haemoglobin
- is an iron(II) complex containing a multidentate ligand
- enables oxygen to be transported in the blood
what reaction occurs when an oxygen molecule is haemoglobin is replaced by a carbon monoxide molecule
ligand exchange reaction
why is CO bad?
- toxic to humans
- the bond made between the CO and haemoglobin is stronger than that with oxygen
- this prevents the oxygen from attaching to the haemoglobin
