Chapter 24 - Transition elements Flashcards
What are d-block elements?
elements that highest energy subshell is a d-subshell found between group 2 and 13
What are some common properties of d-block elements?
Metallic, high melting + boiling pints, shiny, conduct both electricity and heat
What are the 2 irregularities in the d-block in terms of electron configuration?
chromium: 3d54s1 (instead of 3d44s2)
copper: 3d104S1 (instead of 3d94s2)
Why do these irregularities exist in the d-block electron configuration?
A half filled and a fully filled d subshell gives greater stability to these atoms
When forming an ion what subshell does zinc lose electrons from first (empties first)
4s
What is a transition element?
d-block elements that form at least one ion with a partially filled d subshell. (give example - with electron configuration)
Which d-block elements are excluded from being transition elements, and why?
- Scandium - as it only forms the ion Sc3+ by loss of two 4s electrons and one 3d electron
- Zinc - only forms the Zn2+ ion by the loss of its two 4s electrons
Sc3+ has empty d orbital and Zn2+ hass full d orbital
What are the properties of the transition elements and their compounds?
- Form compunds in which the transition element has different oxidation states
- form coloured compounds
- elements and their compounds can act as catalysts
What is the colour of a solution of a transition compound linked to?
The partially filled d-orbitals of the transition metal ion. Varies with different oxidation states
Give 2 transition element coloured compounds
potassium dichromate (VI) - orange
cobalt (II) chloride - pink-purple
Nickel (II) sulphate - green
hydrated copper (II) sulphate - blue
What is the catalyst used in the haber process?
(production of ammonia N2(g) + 3H2 ⇔ 2NH3(g) )
Iron - Fe
What’s the catalyst used in the contact process (production of sulphur trioxide from oxidation of sulfur dioxide)?
2SO2(g) + O2(g) ⇔ 2SO3(g)
vanadium (V) oxide - V2O5(s)
What’s the catalyst used in hydrogenation?
Nickel
What’s the catalyst used in the catalytic decomposition of hydrogen peroxide?
2H2O2(aq) -> 2H2O(l) + O2(g)
Manganese (IV) oxide - MnO2(s)
What catalyst is used for the reaction of zinc metal with acids?
Zn(s) + H2SO4(aq) -> ZnSO4(aq) + H2(g)
Cu2+(aq) ions
What is a complex ion?
Transition metal ion bonded to ligands by coordinate bonds
What’s a ligand?
molecule or ion that donates a pair of electrons to a central metal ion to form a cordinate/dative covalen bond
Define coordination number
number of coordinate bonds attached to the central metal ion
How are complex ion represented in a formula?
[Cr(H2O)6]3+
- square brackets used to group all parts of the complex ion together
- ligand inside round brackets
- overall charge of complex ion. Sum of charges on central metal ion and any ligands present
What’s a monodentate ligand?
ligand that is able to donate one pair of electrons to a central metal ion
Give 6 examples of common monodentate ligands
water, H2O - neutral
ammonia, NH3 - neutral
Thiocynate, SCN - -1
Cyanide, CN - -1
Chloride, Cl - -1
Hydroxide, OH - -1
What are bidentate ligands?
ligands that can donate 2 lone pairs of electrons to the central metal ion, forming 2 coordinate bonds
what are 2 common bidentate ligands?
1,2-diaminoethane and ethanedioate
What does the shape of a complex ion depend upon?
It’s coordination number
What shape is created from a complex ion having a coordination number of 6?
octahedral
Draw [Mn(H2O)6]2+
What shpes can be created from a complex ion having a coordination number of 4?
Tetrahedral and square planar
When is a square planar shape formed in a complex ion?
Occurs in complex ions of transition metals with 8d-electrons in the highest energy d-subshell.
e.g. Platinum (II), Palladium (II) and gold (III)
Draw [CuCl4]2-
Draw [Pt(NH3)4]2+
What are stereoisomers?
Compounds that have the same structural formula but different arrangement of atoms in space
What 2 types of stereoisomerism can complex ions display?
- cis-trans isomerism
- optical isomerism
When can complex ions show cis-trans isomerism?
Some 4-coordinate (square planar) and 6-coordinate (octahedral) complex ions containing two different monodentate ligands
When can complex ions show both types of stereoisomerism?
Some 6-coordinate (octahedral) complex ions containing monodentate and bidentate ligands can show both cis-trans and optical isomerism.
(4 of one type and 2 of another)
Give an example of a square planar complex ion
[Pd(NH3)2Cl2]
Draw the cis and trans isomers of the example
Give an example of an octahedral coplex ion that shows cis-trans isomerism
[Co(NH3)4Cl2]+
*Draw this example (octahedral cis-trans isomers) in both trans and cis form
*Give an example of a octahedral complex ion with bidentate ligands that show stereoisomerism. Draw the isomers
What is optical isomerism?
Compounds that are non superimposible mirror images of each other
What are two optical isomers called?
Enantiomers
*Draw two optical isomers of [Co(NH2CH2CH2NH2)2Cl2]+
When can a complex ion show optical isomerism?
- When it has no lines of symmetry
- Octahedral complexes containing two or more bidentate ligands
e. g.
What is cis-platin and how does it work?
Cis-platin is an anti-cancer drug and works by forming a platinum complex inside of a cell which binds to DNA and stops it from replicating (cell division). Activation of cell’s own repair mechanism leads to apoptosis (systematic cell death)
*Draw the structure of cis-platin
What is ligand substitution?
Reaction in which one ligand in a complex ions is replaced by another ligand.
What is the stability constant, Kstab (for a complex)?
Equilibrium constant for the formation of a complex ion in a solvent from its constitient ions or molecules.
used to compare the stability of ligands relative to the aqueous metal ion where the ligand is water. The larger the Kstab value, the more stable the complex formed is.
If the concentrations of the transition element complex and the reacting ligands are known, the expression for the stability constant (Kstab) can be used to determine which complex is more stable
When copper(II) sulfate is dissolved in water, what is formed? What colour is it?
[Cu(H2O)6]2+ - pale blue
Describe what happens when an excess of aqueous ammonia is added to a solution containing [Cu(H2O)6]2+
Four of the H2O’s are replaced by ammonia ligands. The solution turns from pale blue to dark blue. Forms [Cu(NH3)4(H2O)2]2+
(ligand substitution)
Describe what happens when hydrochloric acid is added to [Cu(H2O)6]2+
HCl used as a source of Cl-ions.
Six water ligands have been replaced with four chloride ligands, forming [CuCl4]2- - pale blue solution turns yellow (as Cl ligands are larger in size than water so less fit around central Cu2+ ion)
In terms of the complex ion what changes in the formation of [CuCl4]2- from [Cu(H2O)6]2+ (ligand substitution) when reacted with chloride ions?
- coordination number (6 -> 4)
- Colour
- Shape
Why does the solution of chloride ions reacting with [Cu(H2O)6]2+ turn green as the reaction proceeds?
Result of yellow colour mixing with the blue
What is formed when chromium (III) potassium sulfate (KCr(SO4)2.12H2O) is dissolved in water? What colour is this?
[Cr(H2O)6]3+ - pale purple solution
What is formed when chromium (III) sulfate is dissolved in water?
What colour is this?
[Cr(H2O)5SO4]+ - green solution
Describe what happens when excess aqueous ammonia is added to [Cr(H2O)6]3+
Ligand substitution occurs, forming [Cr(NH3)6]3+.
Initially a grey-green precipitate of Cr(OH)3 is formed. Cr(OH)3 dissolves in ammonia to form [Cr(NH3)6]3+ which is a purple solution
How is oxygen transported around the body?
Oxygen binds to (Fe2+ in) haemoglobin to form oxyhaemoglobin when blood passes through the lungs, oxygen can be released to body cells when required
Draw the structure of haemoglobin
What ligand substitution takes place fomring carboxyhaemoglobin?
If CO is breathed in, oxygen in haemoglobin is replaced by CO as it binds to haemoglobin more strongly than O2. Coordinate bond wih CO is stronger than O2 (stability constant greater)
Small concentration of CO can prevent large proportion of haemoglobin molecules from carrying oxygen
What is a precipitation reaction?
Reaction that occurs when two aqueous solutions containing ions react together to form an insoluble ionic solid called a precipitate.
Describe the precipitation reaction of Cu2+ with NaOH
blue solution forms blue precipitate of copper (II) hydroxide. Insoluble in excess NaOH
Cu2+(aq) + 2OH-(aq) -> Cu(OH)2(s)
Describe the reactions of Fe2+ and Fe3+ with NaOH(aq)
Fe2+ - pale green solution reacts to form green precipitate of Iron (II) hydroxide - brown at its surface on standing in air as iron is oxidised
Fe2+(aq) + 2OH-(aq) -> Fe(OH)2(s)
Fe3+ - pale yellow solution reacts to form and orange-brown precipitate of Iron (III) hydroxide.
Fe3+(aq) + 3OH-(aq) -> Fe(OH)3(s)
Describe the reaction of Mn2+ with NaOH(aq)
Pink solution reacts to form light brown precipitate of manganese (I) hydroxide which darkens on standing in air.
Mn2+ + 2OH-(aq) -> Mn(OH)2(s)
What happens to the precipitates formed when these hydroxides are reacted with excess NaOH
Nothing
Precipitates are insoluble
Describe the reaction of Cr3+ with NaOH(aq)
Violet solution reacts o form a grey-green precipitate of chromium (II) hydroxide
Precipitate is soluble in excess NaOH forming dark green solution:
Cr3+(aq) -> Cr(OH)3(s) -> [Cr(OH)6]3-
Cr3+(aq) + 3OH-(aq) -> Cr(OH)3(s)
How do Fe2+, Fe3+ and Mn2+ react with an excess of aqueous ammonia?
Some way as they react with NaOH(aq), forming precipitates of Fe(OH)2(s), Fe(OH)3(s) and Mn(OH)2(s)
Why are the results the same when you add ammonia and when you add NaOH to transition metal?
Explain with aid of eqn
NH3 + H20 –> NH4+ + OH-
- Ammonia in aq solution
- OH- is present
What reaction used for oxidation of Fe2+ to Fe3+?
What is the redox reaction for this equation and what is the colour change?
Reaction between Iron(II) ions, Fe2+, and manganate (VII) ions, MnO4-, in acidic conditions.
MnO4-(aq) + 8H+(aq) + 5Fe2+ -> Mn2+(aq) + 5Fe3+(aq) + 4H2O(l)
Solution containing MnO4- ions is purple and is decolourised by Fe2+(aq) ions to form a colourless solution containing Mn2+(aq) ions
What reaction used for oxidation of Fe3+ to Fe2+?
What is the redox reaction for this equation and what is the colour change?
Solution of Fe3+(aq) ions reacts with iodidde ions, I-(aq)
2Fe3+(aq) + 2I-(aq) -> 2Fe2+(aq) + I2(aq)
Orange brown Fe3+(aq) ions are reduced to pale green Fe2+(aq) ions. This colour change is obsured by the brown iodine (oxidised from I-) formed.
What reaction used for the reduction of Cr2O72- to Cr3+?
What is the redox reaction for this equation and what is the colour change?
Acidified Cr2O72(aq) ions can be reduced to Cr3+ (aq) ions by addition of zinc
Cr2O72(aq) + 14H+(aq) + 3Zn(s) -> 2Cr3+(aq) + 7H2O(l) + 3Zn2+(aq)
Cr2O72(aq) ions have an orange colour and Cr3+(aq) have a green colour
What is formed when chromium (III) ions are reacted with an excess of zinc?
Write the redox reaction?
Chromium (II) ions - paleblue colour
Zn(s) + 2Cr3+(aq) -> Zn2+(aq) + 2Cr2+(aq)
What reaction used for the oxidation of Cr3+ to CrO42-?
What is the redox reaction for this equation
Hot alkaline H2O2 reacted with Cr3+
3H2O2 + 2Cr3+ + 10OH- -> 2CrO42- + 8H2O
What reaction used for the reduction of Cu2+ to Cu+?
What is the redox reaction for this equation
When aqueous Cu2+ ions react with excess iodide ions, I-(aq), CuI forms
Copper iodide is a white precipitate
2Cu+(aq) + 4I-(aq) -> 2CuI(s) + I2(s)
What reaction shows he disproportionation of Cu+ ions?
Solid copper (I) oxide, Cu2O, reacts with hot dilute sulphuric acid to form brown precipitate of copper and blue solution of copper (II) sulfate. Cu+ has been reduced and oxidised
Cu2O(s) + H2SO4(aq) -> Cu(s) + CuSO4(aq) + H2O(l)
