24 Transition elements Flashcards
What are d-block elements?
The elements located between Group 2 and Group 13.
What are the properties of d-block elements?
They’re all metallic so:
- High melting and boiling points
- Shiny in appearance
- Conduct both electricity and heat
What are some common uses of d-block elements?
- Copper,silver,nickel,zinc in Coinage
- Iron in Construction and production of tools
- Copper in electrical cables and water pipes
- Titanium in aerospace industry, joint replacement and cosmetic dentistry
Why do chromium and copper not follow the expected principle?
- For stability
- It’s believed that a half filled d5 subshell and a fully filled d10 subshell gives additional stability to atoms of chromium and copper.
What is the configuration of chromium?
3d5 4s1
What is the configuration of copper?
3d10 4s1
When forming an atom…
the 4s orbital fills before the 3d orbitals
When forming an ion…
the 4s orbital empties before the 3d orbitals.
What are transition elements defined as?
D-block elements that form at least one ion with a partially filled d-orbital.
How does scandium form the ion Sc3+ ?
By the loss of two 4s electrons and one 3d electron.
How does zinc form the ion Zn2+ ?
By the loss of its two 4s electrons.
Why are Sc3+ and Zn2+ ions not classified as transition elements?
- Scandium only forms the ion Sc3+ by loss of two 4s electrons and one 3d electron.
- Therefore Sc3+ ions have empty d-orbitals
- Zinc forms the ion Zn2+ by the loss of two 4s electrons.
- Therefore Zn2+ ions have full d-orbitals
- So scandium and zinc do not form ions with partially filled d-orbitals and are not classified as transition elements.
What characteristics do transition elements have?
- They form compounds in which the transition element has different oxidation states.
- They form coloured compounds.
- The elements and their compounds can act as catalysts.
What makes a strong oxidising agent?
A species containing a transition element in its highest oxidation state.
What are the colours of some transition elements?
- Potassium dichromate (VI) : bright orange
- Cobalt (II) chloride: Pink-purple
- Nickel (II) sulfate: Green
- Hydrated copper (II) sulfate: Blue
What is the colour of a solution linked to?
The partially filled d-orbitals of the transition metal ion.
Iron forms two common oxidation states +2 and +3. What are the colours of the solutions?
- Iron (II): Pale green
- Iron (III): Yellow
Chromium forms two common oxidation states +3 and +6. What are the colours of the solutions?
- Cr (III): Green
- Cr (VI): Yellow/Orange
In which process is an iron catalyst used?
- The Haber process.
- For the manufacture of ammonia from the reaction between nitrogen and hydrogen.
In which process is a vanadium oxide catalyst used?
- The Contact process.
- For the production of sulfur trioxide from the oxidation of sulfur dioxide.
What are these catalysts an example of?
Heterogenous catalysts as the catalyst is in a different physical state to the reactants.
What is a complex ion?
A transition metal ion bonded to ligands by coordinate bonds
What is a ligand?
A molecule or ion that donates a pair of electrons to a central metal ion to form a coordinate bond or dative covalent bond.
What is the coordination number?
It indicates the number of coordinate bonds attached to the central metal ion.
What is a monodentate ligand?
A ligand that is able to donate one pair of electrons to a central metal ion.
What is a bidentate ligand?
A ligand that can donate two lone pairs of electrons to the central metal ion, forming two coordinate bonds
E.g ethanedioate ion, 1,2-diaminoethane
What shapes do six-coordinate complexes have?
Octahedral shape, bond angle= 90
What shapes do four coordinate complexes have?
Tetrahedral, bond angle= 109.5
Square planar, bond angle= 90
Examples of tetrahedral complexes
[CoCl4]2-
[CuCl4]2-
Example of square planar complexes
[Pt(NH3)4]2+
Which complex ions show cis-trans isomerism?
Four-coordinate & six-coordinates (Square planar and octahedral)
2 different monodentate ligands
Which complex ions show optical isomerism?
Octahedral complexes containing two or more bidentate ligands
Example of cis-trans isomerism in square planar complexes
[Pd(NH3)2Cl2]
Cis: 90 degrees apart
Trans: 180 degrees apart
Example of cis-trans isomerism in octahedral complexes
MONODENTATE LIGANDS: [Co(NH3)4Cl2]+
BIDENTATE LIGANDS: 1,2-diaminoethane
[Co(NH2CH2CH2NH2)2Cl2]
What are optical isomers?
Stereoisomers that are non-superimposable images of each other, also called ‘enantiomers’
What is a ligand substitution reaction?
A reaction in which one or more ligands in a complex ion are replaced by different ions.
What is the colour change when an excess of AQUEOUS AMMONIA is added to a solution containing [Cu(H2O)6]2+ ?
PALE BLUE-> DARK BLUE
How many ammonia ligands replace the water ligands? & the equation of ligand substitution with ammonia
FOUR AMMONIA ligands replace FOUR OF THE WATER ligands
[Cu(H2O)6]2+ (aq) + 4NH3 (aq) -> [Cu(NH3)4(H2O)2]2+ (aq) + 4H2O (l)
Both are OCTAHEDRAL COMPLEXES
What is formed in the first stage of ligand substitution with ammonia? [Cu(H2O)6]2+
A pale blue precipitate of Cu(OH)2 is formed
What happens in the second stage of ligand substitution with ammonia? [Cu(H2O)6]2+
The Cu(OH)2 precipitate then dissolves in the excess ammonia to form a dark blue solution
What is the colour change when an excess of CONC. HYDROCHLORIC ACID is added to a solution containing [Cu(H2O)6]2+ ?
PALE BLUE -> YELLOW SOLUTION
How many chloride ligands replace the water ligands? & the equation of ligand substitution with HCL
FOUR chloride ligands replace the six water ligands. This is because chloride ligands are larger in size, so fewer can fit around the central Cu2+ ion.
[Cu(H2O)6]2+ (aq) + 4Cl- (aq) -> [CuCl4]2- (aq) + 6H2O (l)
[CuCl4]2- has a TETRAHEDRAL SHAPE
What forms when chromium (III) potassium sulfate, KCr(SO4)2.12(H2O) dissolves in water?
The complex ion [Cr(H2O)6]3+ is formed.
What is the colour change when an excess of AQUEOUS AMMONIA is added to a solution containing [Cr(H2O)6]3+ ?
VIOLET -> PURPLE
What is the equation for the reaction when an excess of aqueous ammonia is added to [Cr(H2OO)6]3+?
[Cr(H2O)6]3 (aq) + 6NH3 (aq) -> [Cr(NH3)6]3+ (aq) + 6H2O (l)
What are the two distinct steps of the reaction between [Cr(H2O)6]3+ and an excess of aqueous ammonia?
1) Initially a grey-green precipitate of Cr(OH)3 is formed.
2) The Cr(OH)3 precipitate dissolves in excess ammonia to form the complex ion [Cr(NH3)6]3+ .
What is the complex called when carbon monoxide binds to the Fe2+ ion in haemoglobin?
Carboxyhaemoglobin
What happens when carbon monoxide is breathed in?
- A ligand substitution reaction takes place where the oxygen in haemoglobin is replaced by carbon monoxide.
- Carbon monoxide binds to haemoglobin more strongly than oxygen, so a small concentration of carbon monoxide in lungs can prevent a large proportion of haemoglobin molecules from carrying oxygen.
- The bond is so strong that the process is irreversible.
What is a precipitation reaction?
The formation of a solid from a solution during a chemical reaction.
When does a precipitation reaction occur?
It occurs when two aqueous solutions containing ions react together to form an insoluble ionic solid calling a precipitate.
What is the observation when Cu2+ ions react with aqueous sodium hydroxide? (NaOH)
- Blue solution reacts to form a blue precipitate of copper (II) hydroxide.
- The precipitate is insoluble in excess NaOH.
Cu2+ (aq) + 2OH- (aq) -> Cu(OH)2 (s)
What is the observation when Fe2+ ions react with aqueous sodium hydroxide? (NaOH)
- Pale green solution reacts to form a green precipitate of iron (II) hydroxide.
- The precipitate is insoluble in excess NaOH but turns brown at its surface due to iron (II) being oxidised to iron (III).
Fe2+ (aq) + 2OH- (aq) -> Fe(OH)2 (s)
In air: Fe(OH2) (s) -> Fe(OH)3 (s)
What is the observation when Fe3+ ions react with aqueous sodium hydroxide? (NaOH)
- Pale yellow solution reacts to form an orange brown precipitate of iron (III) hydroxide.
- The precipitate is insoluble in excess sodium hydroxide.
Fe3+ (aq) + 3OH (aq) -> Fe(OH)3 (s)
What is the observation when Mn2+ ions react with aqueous sodium hydroxide? (NaOH)
- Pale pink solution reacts to form a light brown precipitate of manganese (II) hydroxide which darkens on standing air.
- The precipitate is insoluble in excess sodium hydroxide.
Mn2+ (aq) + 2OH- (aq) -> Mn(OH)2 (s)
What is the observation when Cr3+ ions react with aqueous sodium hydroxide? (NaOH)
- Violet solution reacts to form a grey-green precipitate of chromium (III) hydroxide.
Cr3+ (aq) + 3OH- (aq) -> Cr(OH)3 (s) - The precipitate is soluble in excess sodium hydroxide forming a dark green solution.
Cr(OH)3 (s) + 3OH- (aq) -> [Cr(OH)6]3- (aq)
What is the observation when Cu2+ ions react with an excess of aqueous ammonia? (NH3)
- 1st stage: precipitation reaction: Cu2+ (aq) + 2OH- (aq) -> Cu(OH)2 (s)
- Cu(OH)2 is a blue precipitate which dissolves in excess ammonia to form a deep blue solution- [Cu(NH3)4(H2O)2]2+ .
What is the observation when Cr3+ ions react with an excess of aqueous ammonia? (NH3)
- 1st stage: precipitation reaction: Cr3+(aq)+ 3OH- (aq) -> Cr(OH)3 (s)
- Cr(OH)3 is a green precipitate which dissolves in excess ammonia to form [Cr(NH3)6]3+ which is a purple solution.
What is the reaction between Fe3+, Fe2+ and Mn2+ with an excess of aqueous ammonia?
- They react in the same way as they react with aqueous sodium hydroxide, forming precipitates of Fe(OH)2 , Fe(OH)3 and Mn(OH)2.
- There is no further reaction and so precipitates don’t dissolve.
