Transition metals Flashcards
What is a transition metal?
has an incomplete d-subshell either as an element or as one of its common ions
What are the four characteristics of transition metals?
-can form complexes
-can form coloured ions
-have variable oxidation states
-catalytic activity
Why is copper a transition metal?
-although the atom of copper does not have an incomplete d-subshell
-but Cu2+ does have an incomplete d-subshell
Why is zinc not a transition metal?
neither zinc nor Zn2+ have an incomplete d-subshell
What is the most common ion complex shape, bond angle, and coordination number?
octahedral, 90, 6
How many monodentate ligands can form?
6 coordinate bonds to the central metal ion
What is a complex ion?
consists of a central transition metal ion with ligands that are covalently bonded to it via coordinate bonds
What is a ligand?
a species that can donate one or more pairs of electrons to the metal ion
What are monodentate ligands?
form one co-ordinate bond to the central metal ion
What are some monodentate ligands?
H2O, NH3, Cl-, OH-, CN-
What is a bidentate ligand?
form two co-ordinate bonds to the central metal ion
What are some bidentate ligands?
1,2-diaminoethane (H2NCH2CH2NH2) , ethanedioate (C2O42-)
What can you shorten 1,2-diaminoethane to?
en
What are multidentate ligands?
form three or more co-ordinate bonds to the central metal atom
What is an example of a multidentate ligand?
H2EDTA can form the anion EDTA4- which can form 6 bonds with the metal ion and completely surrounds it
What are chelates?
the complexes formed when bidentate or multidentate ligands bond to a central metal ion
Why are chelate complexes more stable?
their formation results in an increase of entropy/increase in disorder since more chemical species are formed - chelate effect
Name some uses of EDTA?
-remove dangerous metal ions from blood - antidote to metal poisoning
-used in blood transfusions to remove calcium ions to stop clotting
What is haem?
an iron(II) complex with a multidentate ligand, with atoms octahedrally around iron(II)
How does haemoglobin transport oxygen around the body?
oxygen molecules form weak bonds with the iron(II)
Why is carbon monoxide toxic?
it can replace oxygen co-ordinately bonded to Fe(II) in haemoglobin, as it forms a stronger bond - therefore reducing the oxygen-carrying capacity
What are smaller ligands?
H2O, NH3
What are larger ligands?
halide ions
What shape of complex is more likely to form with larger ligands?
tetrahedral
Why do fluoride ions not form tetrahedral coplexes?
the F- ions are smaller than Cl- ions
What is a less common complex shapes?
square planar - 90degrees
What is an example of a square planar shape?
cisplatin - Cl –> … <–NH3
…………………….Pt…………….
…………….Cl –> … <–NH3
What is cisplatin and how does it work?
-an anti-cancer drug used in chemotherapy
-works by preventing DNA replication in cancer cells
-does a ligand-replacement reaction with DNA in which a co-ordinate bond is formed between platinum and a nitrogen atom on guanine
-a second nitrogen from another guanine can replace the second chlorine too
-causes the strands to kink and can’t unwind properly
What are the side effects of cisplatin?
-binds to healthy cells too
-hearing loss
-nausea
-kidney damage
Give an example of a linear complex
tollens reagent - [NH3 –> Ag <– NH3]+
SILVER IONS AND COPPER(I) IONS TEND TO FORM LINEAR COMPLEXES
Why are transition metal complexes coloured?
-they can absorb visible light, but only some
-reflected light contains the frequencies that are not absorbed
What can affect the colour of the transition metal ion?
-type of ligand
-coordination number
-oxidation state of the transition metal
What is a d-d transition?
electrons in the lower 3d subshell absorb energy from visible and UV light radiation which excites/promotes them to the higher 3d subshell
What dictates the frequency of visible light absorbed?
the ΔE between the 2 sets of 3d subshells
When are more intense colours observed?
when the electron moves from a ligand orbital to a metal - charge transfer transitions
How to calculate ΔE?
ΔE = hc/λ
ΔE = hv
h - plancks constant
c - speed of light
v - frequency
λ - wavelength(m)
Why do transition metals have variable oxidation states?
the 4s and 3d electrons are both available for bonding
Apart from scandium (+3), what is the oxidation state of the first row of transition metals?
+2 - loss of 4s electrons. more stable as the increasing nuclear charge causes the 3d electrons to be held more tightly
What is the oxidation state of manganese?
+7
What is a property of the lower oxidation states?
-simple ions
-said to be reducing
What is a property of the higher oxidation states?
-found in complex ions/compounds with very electronegative elements like oxygen (CrO7 2-, VO2 +)
-said to be oxidising
