Topic 15 Transition metals Flashcards
Transition metal
Stable ion with a partially filled d-subshell
Which two transition metals only have one electron in the 4s orbital
Chromium and Copper
An electron from the 4s orbital moves into the 3d orbital to create a more stable half full or full 3d subshell
Which two d-block elements are not transition metals
What ions do they form
Scandium and Zinc
Scandium form only 1 stable ion for Sc3+ - empty d-subshell
Zinc forms one stable ion of Zn2+ - full d-subshell
What is a complex ion
Where a central transition metal surrounded by ligands bonded by coordinate bonds
Ligand
is an ion/atom or molecule that has at least 1 lone pair of electrons
What are Monodentate ligands
Ligands that have 1 lone pair of electrons
H2O, NH3, Cl-, OH-
What are Bidenetate ligands
Ligand which have 2 lone pairs of electrons
Dicarboxylate ion, NH2CH2CH2NH2
Multidentate Ligands
Give an example
LIgands that have more than 1 coordinate bond
EDTA4- can for 6 coordinate bonds with one metal ion
complexes with six ligand coordinate bonds have a WHAT shape
What is the bond angle
Octahedral shape
90° bond angle
Transition metal complex can bond to how many Cl- ions
What shape does this give
What bond angle is this
4 coordinate bonds
Tetrahedral shape
109.5° bond angle
Which compound has 4 ligands bonded but doesn’t have a tetrahedral shape
What is it’s bond angle
cis-platin
Has a square planar shape due to there being two lone pairs
Bond angle of 90°
What shape is haemoglobin
What type of ligand bonds to form it
Octahedral
Made from a multidentate ligand
4 of the nitrogen come from the multidentate ligand - haem
1 of the coordinate bonds comes from large protein called globin
Final coordinate bond comes from either oxygen/water
How does haemoglobin carry oxygen in the blood
oxygen substitutes the water ligand in the lungs where the oxygen concentration is high forming oxyhaemoglobin
THen oxyhaemoglobin gives up oxygen to a place where it is needed, water takes its place
What is the problem with carbon monoxide and haemoglobin
Water ligand is replaced by carbon monoxide ligand
However, the bond with carbon monoxide is so strong it cannot be replaced with oxygen/water again
So oxygen cannot be transported from the lungs
Which type of ligand can show optical isomerism
Octerherdral complexes with 3 bidentate ligands
What shape of complex can have cis-trans isomerism
octahedral complexes with 4 ligands of the same type and 2 ligands of a different type
To different ligands opposite another - trans
Two ligands are adjacent - cis
Describe the difference between cis-platin and trans-platin
Cis- on the same side of the platinum
Trans - on the opposite side of the platinum
Why can transition metals have variable oxidation states
due to the electrons in 3d and 4s subshell being close together
as a result, electrons are gained and lost using a similar amount of energy when they form ions
When does the d-orbital split
Why does this produce a colour
when ligands bond with the central metal ions
It causes some orbitals to gain energy- an energy gap is created - ΔE
When electrons absorb light some move from the lowest energy state (ground state) to higher energy level orbitals(excited state)
In order for this to happen energy must equal ΔE
What is the size of ΔE dependent on
central metal ion and it’s oxidation state
Type of ligand
Coordination number
How do complementary colours link to ΔE
The frequencies that are absorbed = ΔE
We then view a complementary colour for the light which is reflected
Why do some d-block elements not produce a complimentary colour
For complexes where there are full or empty 3d subshells, no electrons migrate to a higher energy level
These complexes are white
How does redox potential link to transition metals
The least stable ions have the largest redox potential
are more likely to be reduced
Positive = reduced
What are the standard conditions for measuring redox potentials
- 298K
- 100kPa
- 1 moldm-3
What are the 4 oxidation states of vanadium and the colours
V2+ - Violet
V3+ - Green
VO2+ - Blue
VO2+ - Yellow
What element can we use to reduce vanadium
How far can we reduce vanadium
VO2+ ⇢ VO2+ = yellow to blue
VO2+ ⇢ V3+ = blue to green
V3+ ⇢ V2+ = green to violet
What are the 4 chromium complexes you need to know about
Cr2O72+ = Orange
CrO42- = Yellow
Cr3+ = Green
Cr2+ = Blue
What can use to reduce chromium
How far can you reduce it
What is the problem however
Zinc
From Cr2O72+ ⇢ Cr3+ = Orange to green (what happens in oxidation of alcohols)
Cr3+ ⇢ Cr2+ = Green to blue
Cr2+ is very unstable and will readily oxidise back to Cr3+ with oxygen in the air
What can you use to oxidise Chromium
How far can you oxide it
Hydrogen peroxide (H2O2)
From Cr3+ to Cr2O72- = from green to orange
Which two ions of Chromium exist within equilibrium
CrO42- and Cr2O72-
Adding acid to yellow CrO42- creates orange Cr2O72-
Which complexion of Chromium is Amphoteric
What colour is it
How is it made
[Cr(H2O)3(OH)3] - Which is a green/grey precipitate
It can be made by adding 3OH-/3NH3 to green [Cr(H2O)6]3+
When [Cr(H2O)3(OH)3] reacts with acid or alkali, what type of reaction occurs
acid/base reaction
What happens when you add excess ammonia to [Cr(H2O)3(OH)3]
What would be the colour change
What type of reaction is this
[Cr(H2O)3(OH)3] + 6NH3 ⇢ [Cr(NH3)6]3+ + 3H2O + 3OH-
Goes from green/grey solid to purple
Ligand exchange reaction
What colour is Copper2+ in aqueous solutions
What is it’s structure
Blue
[Cu(Η2Ο)6]2+
What colour is Iron 2+ in aqueous solution
What is it’s structure
[Fe(Η2Ο)6]2+
Pale green coloured
What colour is Iron 3+ in aqueous solution
What is it’s structure
Yellow
[Fe(Η2Ο)6]3+
What is the colour of Cobalt 2+ in aqueous solution
What is it’s structure
Pale pink
[Co(Η2Ο)6]2+
What is the colour of the precipitate when 2NH3/2OH- are added to [Cu(Η2Ο)6]2+
What is it’s structure
Pale blue precipitate
Cu(OH)2(Η2Ο)4
What is the colour of the solution produced when 6NH3 is added to Cu(OH)2(Η2Ο)4
What is the structure of the product
Dark blue solution
[Cu(ΝΗ3)4(Η2Ο)2]2+
What is the colour of the precipitate when 2NH3/2OH- are added to [Fe(Η2Ο)6]2+
What is the structure of the product
Dirty green precipitate
Fe(OH)2(Η2Ο)4
What is the colour of the precipitate when 3NH3/3OH- are added to [Fe(Η2Ο)6]3+
What is the structure of the product
Orange precipitate
Fe(OH)3(Η2Ο)3
What is the colour of the precipitate when 2NH3/2OH- are added to [Co(Η2Ο)6]2+
What is it’s structure
Blue precipitate - turns brown after a while
Co(OH)2(Η2Ο)4
What is the colour of the solution when Co(OH)2(Η2Ο)4 reacts with 6NH3
What is the structure of the product
What type of reaction is it
Brown/Yellow solution
Co(NH3)62+
Ligand exchange
What would be the colour change associated with this reaction
[Cu(Η2Ο)6]2+ +4Cl- ⇢ [CuCl4]2−
What type of reaction is it
from blue to yellow
ligand exchange and coordination number
What would be the colour change associated with this reaction
[Co(Η2Ο)6]2+ +4Cl- ⇢ [CoCl4]2−
What type of reaction is it
Pink to blue
ligand substitution and coordination number
substitution of a monodentate ligand by a bidentate or multidentate ligand leads to a more stable complex ion, why?
the large positive increase in ΔSsystem
Due to more molecules being in multidentate ligands than mono/bidentate ligands
Describe the contact process
Which transition metal is used as a catalyst
To produce sulphuric acid
Vanadium is the catalyst
SO2 + V2O5 ⇢ SO3 + V2O4
V2O4 + 0.5O2 ⇢ V2O5
Which transition metal catalyses the reaction between I− and S2O82− ions
Fe2+
- S2O82− + 2Fe2+ ⇢ 2Fe3+ + SO42-
- 2Fe3+ + I- ⇢ 2Fe2+ + I2
What ion is used in autocatalysing the reaction between MnO4− and C2O42− ions
Mn2+
- MnO4− + 8H+ + 4Mn2+ ⇢ 5Mn3+ + 4H2O
- 2Mn2+ + C2O42− ⇢ Mn2+ + 2CO2
