20: Transition Elements Flashcards
What is a transition element
An element that forms one or more stable ions with an incomplete d sub-shell
What 2 transition metals do not follow the simple pattern of filling up sub-shells
Chromium
Copper
What is the electron configuration of Chromium
1s²2s²2p⁶3s²3p⁶3d⁵4s¹
What is the electron configuration of Copper
1s²2s²2p⁶3s²3p⁶3d¹⁰4s¹
Why are Sc and Zn not considered as transition metals even though they are d block elements
Scandium’s only stable ion is Sc³† which has 0 electrons in the d sub-shell
Zinc’s only stable ion is Zn²† which has a completely full d sub-shell
What are 3 characteristics of transition metals
Variable oxidation states in compounds
The metal and their compounds are often catalytically active
Their compounds are usually coloured
Demonstrate how transition metals have variable oxidation states in compounds
Iron commonly exists in +2 and +3 oxidation states
Can show this by Fe(OH)₂ and Fe(OH)₃
Examples of transition metals acting as catalysts
Ni is used as a catalyst in the reduction of alkenes and nitriles to form alkanes and amines respectfully.
FeCl₃ can be used as a catalyst for chlorination of benzene
Why are catalysts important for industrial use
They can reduce energy usage by allowing reactions to take place at lower temperatures.
They can allow alternative reactions to be used which otherwise would be too slow to take place under reasonable conditions. Such processes may be advantageous in terms of better percentage yield or atom economy
What is a hexaaqua ion
A complex ion containing six water molecules
What is the colour of [Cr(H₂O)₆]³†
Violet
But it is commonly green because one or more of the water ligands is replaced by an anion from the solution.
What is the colour of [Fe(H₂O)₆]³†
Yellow
What is the colour of [Mn(H₂O)₆]²†
Pale pink
What is the colour of [Cu(H₂O)₆]²†
Blue
What is the colour of [Fe(H₂O)₆]²†
Pale green
What is a complex ion
A metal ion bonded to a number of ligands which donate electron pairs to form dative covalent bonds (coordinate bonds)
What is a ligand
An ion or molecule with a lone pair of electrons which it donates to a central metal ion by forming a dative covalent bond (coordinate bond) with it
What is a unidentate ligand
Ligands that have a single point of attachment to the ion
Forms 1 dative covalent bond
What is a bidentate ligand
Ligand that coordinates the metal ion through two separate atoms, each of which donates a lone pair to form a dative covalent bond
What is the co-ordination number
The co-ordination number of an ion in a complex is the number of ligand lone pairs that are bound to it, ie the number of coordinate bonds formed to the metal
What factor affects coordination number
The size of the ligand
Can’t fit 6 larger ligands like Cl¯
H₂O is smaller so you can fit 6 on the metal
What shape molecule does Pt form
Square planar
What are the bond angles between ligands in square planar
90º or 180º
What are the bond angles between ligands in an octahedral complex
90º or 180º
What reasons are there for why a ligand substitution reaction happens
- A ligand capable of forming stronger coordinate bond to the metal ion may replace one which forms weaker coordinate bonds
- A ligand added at high concentration may replace one at a lower concentration
Which metal ion turns from blue to green to yellow when HCl is added
aqueous Copper (II)
Describe the colour change when HCl is added to aqueous copper (II) ions
Blue to green to yellow
What is the colour change of addition of excess aqueous ammonia to aqueous copper (II) ions
Blue → Deep blue
Write the equation for addition of excess aqueous ammonia to aqueous copper (II) ions
[Cu(H₂O)₆]²†(aq) + 4NH₃(aq) ⇌ [Cu(NH₃)₄(H₂O)₂]²†(aq) + 4H₂O(l)
Only 4 of the 6 water ligands are substituted by ammonia
What is the colour change seen when excess aqueous ammonia is added to chromium (III) ions
violet to purple
Write the equation for when excess aqueous ammonia is added to chromium (III) ions
[Cr(H₂O)₆]³†(aq) + 6NH₃(aq) ⇌ [Cr(NH₃)₆]†³(aq) + 6H₂O(l)
All of the water is substituted
What happens to haemoglobin in the lungs (high [O₂])
The oxygen replaces the water ligand around the Fe²† ion
This allows the haemoglobin to transport oxygen around the body
What happens to haemoglobin in active muscles (Low [O₂] )
Water replaces the oxygen ligand around the Fe²†
Oxygen is released into the muscles
Why is CO poisonous
Carbon monoxide is a better ligand than oxygen (it can form stronger coordinate bonds to Fe²†) so it replaces oxygen.
Haemoglobin can no longer carry oxygen so the body has oxygen deficiency
What is the angle between two of the same ligands in a cis isomer
90º
What is the angle between two of the same ligands in a trans isomer
180º
What is used cis-platin used for
Treating cancer
How does cis-platin treat cancer
It prevents tumour growth by binding to DNA, thereby stopping cell division
How does the bond angle in NH₃ change when it acts as a ligand
NH₃ has a bond angle of 107º because it has 3 bonding pairs and a lone pair
When NH₃ acts as a ligand the lone pair is converted to a dative covalent bond so the bond angle is now 109.5º as it has 4 bonding pairs and no lone pairs
What do 2+ and 3+ ions of transition metals form when sodium hydroxide is added
Insoluble hydroxides
What is the colour of the precipitate formed when a limiting amount of sodium hydroxide reacts with Cr³†
Green precipitate
What is the colour of the precipitate formed when sodium hydroxide reacts with Mn²†
Light brown precipitate
What is the colour of the precipitate formed when sodium hydroxide reacts with Fe²†
Green precipitate
What is the colour of the precipitate formed when sodium hydroxide reacts with Fe³†
Orange-Brown precipitate
What is the colour of the precipitate formed when sodium hydroxide reacts with Cu²†
Blue precipitate
What happens when excess sodium hydroxide is added to Cr³†
The Cr(OH)₃ precipitate will redissolve to form a complex ion, [Cr(OH)₆]³¯ Resulting in a dark green solution
Cr(OH)₃(s) + 3OH¯(aq) → Cr(OH)₆³¯
What happens when aqueous ammonia is added to aqueous 2+ and 3+ transition metal ion
Ammonia is weakly basic so will react with water:
NH₃(aq) + H₂O(l) ⇌ NH₄†(aq) + OH¯(aq)
The OH¯ ions will react with the transition metal ions to form a insoluble hydroxide.
These hydroxides are the same as the ones produced when NaOH(aq) is added so have the same colours
Colour change when excess ammonia is added to Cu(OH)₂(s)
Blue solid → Deep blue solution
Equation for the reaction of excess ammonia added to Cu(OH)₂(s)
Cu(OH)₂(s) + 4NH₃(aq) + 2H₂O(l) → [Cu(NH₃)₄(H₂O)₂]²†(aq) + 2OH¯
Which hydroxides will redissolve when excess ammonia is added
Cu(OH)₂(s) and Cr(OH)₃(s)
Colour change when excess ammonia is added to Cr(OH)₃(s)
Green solid → Purple solution
Equation for the reaction of excess ammonia added to Cr(OH)₃(s)
Cr(OH)₃(s) + 6NH₃(aq) → [Cr(NH₃)₆]³†(aq) + OH¯(aq)
What agent is used to oxidise Fe²†(aq) to Fe³†(aq)
Aqueous acidic potassium manganate(VII)
Colour change of oxidising Fe²†(aq) to Fe³†(aq) using potassium manganate(VII)
pale green to yellow-brown
What agent is used to reduce Fe³†(aq) to Fe²†(aq)
Iodide
What colour is the solution when iodide is used to reduce Fe³†(aq) to Fe²†(aq)
Aqueous I₂ is formed, so the solution turns brown
What agent is used to oxidise Cr³†(aq) to CrO₄²¯
Hydrogen peroxide
What is the colour change when hydrogen peroxide is used to oxidise Cr³†(aq) to CrO₄²¯
Violet or green to yellow
How can Cr₂O₇²¯ be created form CrO₄²¯
By adding aqueous acid
2CrO₄²¯ + 2H† → Cr₂O₇²¯ + H₂O
What is the colour of Cr₂O₇²¯
Orange
What agent is used to reduce Cr₂O₇²¯ to Cr³†
Zn, under acidic conditions
What is the colour change when Zn(acidic conditions) is used to reduce Cr₂O₇²¯ to Cr³†
Orange to green
What agent is used to reduce Cu²† to Cu†
Iodide
What is the colour change when iodide is used to reduce Cu²† to Cu†
Blue solution → White solid + brown solution
CuI(s) is white
I₂(aq) is produced which is brown
What is the result of Cu† not being stable in aqueous solutions
It disproportionates
2Cu†(aq) → Cu²†(aq) + Cu(s)
Equation for Cu₂O(s) + acid
it disproportionates
Cu₂O(s) + 2H†(aq) → Cu(s) + Cu²†(aq) + H₂O(l)
Colour change of Cu₂O(s) reacting with acid
Red solid → pink metallic solid + blue solution
Cu₂O(s) + 2H†(aq) → Cu(s) + Cu²†(aq) + H₂O(l)
