Module 5 Section 3: Transition Elements Flashcards
What types of elements are d block elements
D-block elements are all metallic
Transition metal characteristics
High melting points and boiling points
Shiny in appearance
Conduct both electricity and heat
Uses of transition metals
Copper, silver, nickel, zinc: coinage
Iron: construction and tools
Copper: electrical appliances and water pipes
Titanium: aerospace industry and medical applications (joint replacements)
Draw electron configurations of chromium and copper
Why do copper and chromium have exceptional electron configurations
A half filled d5 subshell (chromium) and a fully filled d10 subshell (copper) give additional stability
What happens when the d block elements scandium - zinc form positive ions
Lose their 4s electrons before losing any 3d electrons
When forming an atom the 4s orbital fills before the 3d orbitals
When forming an ion the 4s orbital empties before the 3d orbitals
Explain the exceptional electron configuration of chromium
Chromium prefers to have 1 electron in each orbital of the 3d subshell and just one in the 4s subshell
This gives it more stability
Explain the exceptional electron configuration of copper
Copper prefers to have a full 3d subshell and just one electron in the 4s subshell
It’s more stable that way
Copper forms a stable Cu2+ ion by losing 2 electrons.
The Cu2+ ion has an incomplete d subshell
What happens when iron forms it’s ions
Draw the electron configurations of each
Iron can form Fe2+ and Fe3+ ions
When it forms 2+ ions, it loses both its 4s electrons
Only once the 4s electrons are removed can a 3d electron be removed
Definition of transition metals
A transition element is a d block element that can form at least one stable ion with an incomplete d subshell
Why is scandium not classed as a transition metal
Scandium only forms one ion, Sc3+, which has an empty d sub-shell.
Scandium has the electron configuration 1s2 2s2 2p6 3s2 3p6 3d1 4s2
It loses three electrons to form Sc3+
This has the electron configuration 1s2 2s2 2p6 3s2 3p6
Why is zinc not classed as a transition metal
Zinc only forms one ion Zn2+ which has a full d sub-shell Zinc has the electron configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s2.
When it forms Zn2+ it loses 2 electrons, both from the 4s sub-shell — so it keeps its full 3d sub-shell.
Unique features of transition elements
Transition elements can exist in variable oxidation states
Form different coloured ions
Can make good catalysts
Colours of aqueous solution containing titanium ions
Ti3+: purple
Ti2+: violet
Colours of aqueous solution containing vanadium ions
VO2 +: yellow (1+ charge)
VO2+: blue (2+ charge)
V3+: green
V2+: violet
Colours of aqueous solution containing chromium ions
Cr2O7 2-: orange
Cr3+: pale purple (looks green (I don’t know why either🤷🏻♂️))
Colours of aqueous solution containing manganese ions
MnO4-: purple
MnO4 2-: green
Mn2+: pale pink
Colours of aqueous solution containing iron ions
Fe3+: yellow
Fe2+: pale green
Colours of aqueous solution containing cobalt ions
Co2+: pink
Colours of aqueous solution containing nickel ions
Ni2+: green
Colours of aqueous solution containing copper ions
Cu2+: pale blue
Why do transition metals show variable oxidation states
The energy levels of the 4s and 3d subshells are very close to one another
So different numbers of electrons can be gained or lost using fairly similar amounts of energy
Draw out table of transition metals in 4th period and all their colours for oxidation numbers ranging from +7 to +2
Electron configuration of copper
Electron configuration of chromium
Why do transition elements form coloured ions
Compounds of ions of transition elements are frequently coloured
The solid compounds can be dissolved in water to produce coloured solutions
Colour of a solution is due to partially filled d-orbitals of the transition metal ion
Why can transition elements make good catalysts
Make good catalysts because they can change oxidation states by gaining or losing electrons within their d orbitals
They can therefore transfer electrons to speed up reactions
Transition metals are good at adsorbing substances onto their surfaces to lower activation energy
Uses of heterogenous catalysts made of transition metals in industry
Uses of transition metals in industrial processes:
Finely divided iron catalyst in Haber process to produce ammonia
Vanadium(V) oxide in contact process to produce sulfur trioxide from oxidation of sulfur dioxide
Hydrogenation of vegetable fats in manufacture of margarine uses nickel
Catalytic decomposition of hydrogen peroxide forming oxygen uses manganese(IV) oxide (MnO2)
Reaction of Zn with acids is catalysed by Cu2+ (aq)
Uses of homogenous catalysts made of transition metals in industry
Reaction between peroxodisulfate (S2O82-)and I- ions is catalysed by Fe2+ ions (all in aqueous solutions
Possible dangers of using transition metals as catalysts
Using transition element catalysts can pose health risks as many of the metals and their compounds are toxic
E.g. long term exposure to copper can cause liver and kidney problems, exposure to manganese causes psychiatric problems
What is a complex ion
A complex ion is a metal ion surrounded by coordinately bonded ligands.
What is a coordinate bond/dative bond
Covalent bond in the shared pair that come from the same atom
What is a ligand
A ligand is an atom, ion or molecule that donates a pair of electrons to a central metal atom or ion.
What is a coordination number
The number of coordinate bonds that are formed with central metal atom/ion
What will the coordination number be if the ligands are small
Ligands such as H2O, CN- of NH3
6 can fit around the central metal atom/ion
Coordination number: 6
Octahedral - 90° bond angle
What will the coordination number be if the ligands are large
Ligands such as Cl-
Only 4 can fit around central metal atom/ion
Tetrahedral - 109.5°
Draw displayed formula of [Cu(H2O)6]2+
Copper oxidation state: +2
Octahedral
Draw displayed formula of [Co(NH3)6]2+
Octahedral
Draw displayed formula of [Cu(NH3)4(H2O)2]2+
Octahedral
Draw displayed formula of [CoCl4]2-
Tetrahedral
Draw displayed formula of [NiCl2(NH3)2]
Square planar
What must a ligand have
Must have at least one lone pair of electrons, or it won’t have anything to form a coordinate bond with
What are the different types of ligands called depending on the number of lone pairs
1 lone pair available for bonding: monodentate
2 lone pairs available for coordinate bonding: bidentate
Ligands that form 2 or more coordinate bonds are multidentate
Give examples of monodentate ligands
Give examples of bidentate ligands
What sort of complex ions can create optical isomers with their ligands
Happens in octahedral complexes when 3 bidentate ligands are attached to the central ion
E.g. [Ni(NH2CH2CH2NH2)3]2+
When can cis/trans isomerism exist in complex ions
Happens when there are two different groups involved
Square planar and octahedral complex ions that have at least two pairs of ligands show cis/trans isomerism
Draw the stereoisomerism for [NiCI2(NH3)2]
Draw stereoisomerism for [Cu(NH3)4(H2O)2]2+
Structure of Cis-platin
Complex of platinum(II) with 2 chloride ions and 2 NH3
Square planar shape
How does cis-platin help to cure cancer
The two chloride ligands are very easy to displace.
The cis-platin loses them and bonds to two nitrogen atoms on the DNA molecule inside the cancerous cell instead
This block on its DNA prevents the cancerous cell from reproducing by division.
The cell will die, since it is unable to repair the damage.
Downside to using cis-platin
The downside is that cis-platin also prevents normal cells from reproducing, including blood, which can suppress the immune system and increase the risk of infection.
Cis-platin may also cause damage to the kidneys.
Why does cis-platin have to be in the cis isomer structure
The two chloride ions are next to each other, so this complex is cis-platin.
If they were opposite each other you would have trans-platin, which has different biological effects.
How to get a coloured precipitate from transition metals
When you mix an aqueous solution of transition element ions with aqueous sodium hydroxide (NaOH) or aqueous ammonia (NH3)
you get a coloured hydroxide precipitate
How are transition metals arranged in aqueous solutions
Take the form of [M(H2O)6]ⁿ⁺
Can be written as Mⁿ⁺ as long as metal ion is only bonded to water
Must write our whole formula if it’s bonded to anything else
What is the colour of the precipitate formed when Cu2+ reacts with NaOH or NH3
Goes from pale blue solution to a pale blue precipitate
What is the colour of the precipitate formed when Fe2+ reacts with NaOH or NH3
Goes from pale green solution to dark green precipitate
What is the colour of the precipitate formed when Fe3+ reacts with NaOH or NH3
Goes from yellow solution to orange-brown precipitate
What is the colour of the precipitate formed when Mn2+ reacts with NaOH or NH3
Goes from pale pink solution to a pale brown precipitate
What is the colour of the precipitate formed when Cr3+ reacts with NaOH or NH3
Goes from green solution to dark green precipitate
What type of stereoisomers in complex ions can also form optical isomers
Only cis isomers can form optical isomers
Where are the bonds in a complex ions relatively weaker
The bonds above and below the central atom/ion are longer so they are slightly weaker
Structure of haemoglobin
Haemoglobin contains Fe2+ ions.
The Fe2+ ions form 6 coordinate bonds.
Four of the lone pairs come from nitrogen atoms within a circular part of a molecule called ‘haem’.
A fifth lone pair comes from a nitrogen atom on a protein (globin).
The last position is a water ligand attached to the iron
What type of ligand is haem
Multidentate ligand
How does haemoglobin transport oxygen
In the lungs the oxygen concentration is high, so the water ligand is substituted for an oxygen molecule (O2) forming oxyhemoglobin.
This is carried around the body and when it gets to a place where oxygen is needed
The oxygen molecule is exchanged for a water molecule again
Why is carbomonoxide harmful
If carbon monoxide (CO) is inhaled, the haemoglobin swaps its water ligand for a carbon monoxide ligand, forming carboxyhaemoglobin.
Carbon monoxide is a strong ligand and doesn’t readily exchange with oxygen or water ligands
Means that the haemoglobin can’t transport oxygen any more
What happens when an ionic compound of chromium is dissolved in water and excess ammonia is added dropwise and write the equation
Ionic compound dissociates to form [Cr(H₂O)₆]³⁺ which is PALE PURPLE SOLUTION
[Cr(H₂O)₆]³⁺ reacts with NH3 to form Cr(OH)₃ which is GREY-GREEN PRECIPITATE
This precipitate dissolves in the excess NH3 to form [Cr(NH₃)₆]³⁺ which is PURPLE SOLUTION
What colour does the solution go when ionic compounds containing chromium are dissolved in water
When KCr(SO₄)₂•H₂O is dissolved in water, [Cr(H₂O)₆]³⁺ is formed which is PALE PURPLE SOLUTION
When Cr₂(SO₄)₃ is dissolved in water a solution of [Cr(H₂O)₅(SO₄)]⁺ forms which is GREEN SOLUTION
What happens when Cu(SO₄) is dissolved in water and ammonia is added dropwise and write the equation
Dissolves to form [Cu(H₂O)₆]²⁺ PALE BLUE SOLUTION
NH₃ added dropwise to form Cu(OH)₂ which is PALE BLUE PRECIPITATE
Then Cu(OH)₂ dissolves in excess NH₃ to form [Cu(H₂O)₂(NH₃)₄]²⁺ which is a DARK BLUE SOLUTION
What happens when Cu²⁺ ions are reacted with concentrated HCl and write the equation
HCl is a source of Cl⁻ ions
Cl⁻ ligands are larger than H₂O ligands so complex ion goes from octahedral to tetrahedral as only 4 can fit around it
Goes from PALE BLUE SOLUTION of [Cu(H₂O)₆]²⁺ to YELLOW SOLUTION of [Cu(Cl)₄]²⁻
What ion precipitates do not dissolve in excess ammonia after they are formed
[Fe(OH)₂(H₂O)₄] (s) (Dark green ppt)
[Fe(OH)₃(H₂O)₃] (s) (orange brown ppt)
[Mn(OH)₂(H₂O)₄] (s) (pale brown ppt)
What ion precipitates do dissolve in excess ammonia after they are formed
Cr(OH)₃ (green ppt) -> [Cr(NH₃)₆]³⁺ (purple solution
Cu(OH)₂ (blue ppt) -> [Cu(H₂O)₂(NH₃)₄]²⁺ (dark blue solution)
Write the half equations and full equations for the conversion of Fe²⁺ to Fe³⁺
Oxidised by KMnO₄
Turns from pale green to yellow
Write the half equations and full equations for the conversion of Fe³⁺ to Fe²⁺
Reduced from I⁻
Turns from yellow to pale green
Write the half equations and full equations for the conversion of Cr³⁺ (in [Cr(OH)₆]³⁻) to CrO₄²⁻ and how to turn this product to Cr₂O₇²⁻
Oxidised by H₂O₂ in alkaline conditions
Turns from dark green to yellow
Write the half equations and full equations for the conversion of Cr₂O₇²⁻ to Cr³⁺(in [Cr(OH)₆]³⁻)
Cr₂O₇²⁻ is reduced to Cr³⁺ by acidified zinc
Turns from orange to green
Write the equations for the reaction of Cu²⁺ with iodide and disproportionation after
Cu²⁺ is reduced to copper(I) iodide using iodide ions
Turns from pale blue to white precipitate
Cu⁺ is unstable so spontaneously disproportionates to produce Cu₍ₛ₎ and Cu²⁺₍ₐᵩ₎
Write the equations for the disproportionation for the reaction of Cu²⁺ and disproportionation
Cu²⁺ is reduced to copper(I) iodide using iodide ions
Turns from pale blue to white precipitate
Cu⁺ is unstable so spontaneously disproportionates to produce Cu₍ₛ₎ and Cu²⁺₍ₐᵩ₎
How to find out what transition metals are in a solution
Add NaOH dropwise from a pipette to a test tube containing the unknown solution
It will produce a coloured precipitate
Write out the table of the precipitates formed from the addition of NaOH to Cu²⁺, Fe²⁺, Fe³⁺, Mn²⁺, Cr³⁺
Test for CO₃²⁻ ligands
Add nitric acid to the test compound.
Bubble any gas given off through limewater.
Limewater turns from clear to cloudy if carbonate is present, due to CO₂
Test for Cl⁻, Br⁻ and I⁻ ligands
Cl⁻: Silver nitrate addition results in white precipitate
Br⁻: Silver nitrate addition results in cream precipitate
I⁻: Silver nitrate addition results in yellow precipitate
Test for SO₄²⁻ ligands
Add barium nitrate or barium chloride
White precipitate form
Test for NH₄⁺ ligands
Add cold NaOH to the compound and warm
Hold damp red litmus paper over the solution
Red litmus paper turns blue in presence of ammonia
Why must you be careful what reagent you add to the solution to test for transition metal ions
May introduce ions that can interfere with later tests
E.g: when testing for CO₃²⁻ you could use HCl instead of HNO₃
This would add chloride ions to the sample so you wouldn’t be able to find out whether or not the initial solution had chloride ions or not
