20: Transition Elements Flashcards by Tom Prentice

What is a transition element

An element that forms one or more stable ions with an incomplete d sub-shell

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What 2 transition metals do not follow the simple pattern of filling up sub-shells

Chromium

Copper

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What is the electron configuration of Chromium

1s²2s²2p⁶3s²3p⁶3d⁵4s¹

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What is the electron configuration of Copper

1s²2s²2p⁶3s²3p⁶3d¹⁰4s¹

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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

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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

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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

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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

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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

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What is a hexaaqua ion

A complex ion containing six water molecules

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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.

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What is the colour of [Fe(H₂O)₆]³†

Yellow

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What is the colour of [Mn(H₂O)₆]²†

Pale pink

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What is the colour of [Cu(H₂O)₆]²†

Blue

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What is the colour of [Fe(H₂O)₆]²†

Pale green

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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)

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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

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What is a unidentate ligand

Ligands that have a single point of attachment to the ion

Forms 1 dative covalent bond

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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

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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

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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

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What shape molecule does Pt form

Square planar

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What are the bond angles between ligands in square planar

90º or 180º

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What are the bond angles between ligands in an octahedral complex

90º or 180º

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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¯](aq)

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)