5.3.1 - Transition Metals Flashcards
‘d’ block element def
Highest energy electron is in a ‘d’ orbital
Transition element def
Element forms a stable ion with an incomplete d-subshell
Properties of transition metals
- Contain metallic bonding
- Form giant metallic lattices
- Form coloured compounds
- Variable oxidation states/numbers
- Used as catalysts due to variable oxidation state
Properties of metals
- Generally unreactive/inert
- Form coloured compounds
- Form a giant metallic lattice
- Good conductors of heat
- Good conductors of electricity
- More on photos
From what shell are electrons lost from first to form a positive ion in transition metals?
Lost from the 4s shell first before the 3d shell
Which transition metals have different electron shell configuration properties?
Why?
(4th and 6th transition metals - why?)
- Chromium and Copper
- (4th and 6th transition metals)
- Chromium- 4s contains one electron and 3d orbitals all only contain one electron
- Copper - all 3D orbitals are full, but the 4s only has one electron
- This is because these configs are thought to reduce electron repulsion = more stable
- So element is more stable
Complex ion def
A metal ion bonded to one or more ligands by coordinate bonds (dative covalent bonds)
Ligand def
A molecule or ion that can donate a pair of electrons to the transition metal ion to form a coordinate bond.
Coordination number def
Total number of coordinate bonds formed in the complex ion
Monodentate ligand def
- A ligand that is able to donate one pair of electrons to a central metal ion
- Only one atom in molecule/ion will donate the lone pair into the metal
- can only form one coordinate bond with the central metal ion
Bidentate ligand def
- A ligand that can donate two pairs of electrons to the central metal ion
- Two atoms in the molecule/ion that donate the lone pair to the metal
Three shapes that complex ions can take
Why?
Tetrahedral - many ions have a coordinate number of 4
Gives rise to 4BPs
Square Planar - coordinate number of 4
Has 4BPs in corners of a square
Octahedral - many ions have a coordinate number of 6
Gives rise to 6BPs
Bond angles of each complex ion shape
Tetrahedral - 109.5 Degrees
Square Planar - 90 Degrees
Octahedral - 90 Degrees
Can complex ions display stereoisomerism?
Yes
- cis/trans and optical
What types of stereoisomers can complex ions form?
Cis-trans isomerism
Optical isomerism
Examples of monodentate ligands
-Water
-Ammonia
-Chloride
-
-
Examples of bidentate ligands
- 1, 2-diaminoethane
- ethanedioate ion (oxalate ion)
Formula of cisplatin
Common shape of cisplatin
- Pt(NH3)2Cl2
- Square planar
Stereoisomer def
Same structural formula but a different arrangement of the atoms in space
Type of isomer that can form in square planar shape with 4 coordinate complexes
Cis-trans isomerism
Type of isomerism that can occur in an octahedral shape molecule with 6 coordinate complexes
Cis-trans isomerism
Optical isomerism
Optical isomerism def
- Two compounds which contain the same number and kinds of atoms, and bonds, and different spatial arrangements of the atoms
- But which have non-superimposable mirror images.
- Each non-superimposable mirror image structure is called an enantiomer.
- a type of stereoisomerism
How to differentiate between cis and trans isomerism in six coordinate complexes
Cis:
-Chosen groups are on the same side
Trans:
-Chosen groups are on opposite sides
Can stereoisomerism occur in tetrahedral shapes
Yes - optical isomerism
Octahedral and tetrahedral show optical, but not square planar
Optical isomerism def
Optical isomers are two compounds which contain the same number and kinds of atoms, and bonds, and different spatial arrangements of the atoms, but which have non-superimposable mirror images.
Each non-superimposable mirror image structure is called an enantiomer.
Ligand substitution def
A reaction in which one ligand in a complex ion is replaced by another ligand
Reaction of aqueous copper(II) ions when dissolved in water
- When copper(II) sulfate is dissolved in water:
- Colour change from pale blue complex ion, [Cu(H20)6]2+ is formed in aqueous solution
Ligand substitution of aqueous copper(II) ions with ammonia
- When excess aqueous ammonia is added to a solution containing [Cu(H20)6]2+
- Colour change from pale blue solution to a dark blue solution
- form [Cu(H2O)2(NH3)4]
Ligand substitution of aqueous copper(II) ions with ammonia experiment and observations
- Add reagent(ammonia) drop-wise go solution under test
- so that all observations are recorded
- Two different reactions can be observed:
- A pale blue precipitate of Cu(OH)2 is formed in first stage of the reaction
- Cu(OH)2 precipitate then dissolves in excess ammonia to form a dark blue solution
Ligand substitution of aqueous Copper(II) ions with chloride ions
-Conc. HCl can be used as a source of chloride ions
-When excess of conc. HCl is added to solution of [Cu(H2O)6]2+
-Pale blue solution changes colour to form a yellow solution
-Could form intermediate green solution if blue and yellow solution is mixed carefully together
-Six water ligands have been replaced with four chloride ligands
-Produces aqueous [Cu(Cl)4]2-
Equation: (= means reversible)
[Cu(H2O)6]2+(aq) + 4Cl- = [CuCl4]2-(aq) + 6H20(l)
What changes occur in ligand substitution of aqueous copper(II) ions with chloride ions?
-Colour change: pale blue —> yellow
-Change in coordination no. : 6 —>4
Due to chloride ligands being larger in size than water ligands
Fewer chloride ions can fit around the central Cu2+ ion
-A change in shape: Octahedral —> Tetrahedral
What remains the same in ligand substitution with chloride ions and copper ions?
-Oxidation state of copper remains +2
Reactions with aqueous chromium(III) ions when dissolved in water
-Observations?
- Chromium(III) potassium sulfate - KCr(SO4)2.12(H2O)
- AKA Chrome Alum
-It is dissolved in water
-Complex ion [Cr(H2O)6]3+ is formed
This is a pale purple solution
- (or is it green solution)
-Oxidation state of chromium is 3+
Chromium(III) sulfate dissolved in water reaction and observations
- When chromium(III) sulfate is dissolved in water
- A green solution containing chromium(III) is formed
- This is a complex formed - [Cr(H2O)5(SO4)]+
- One of the water ligands has been replaced by the sulfate ion(SO42-)
-Oxidation state of chromium is 3+
Reaction of aqueous chromium ions with ammonia and observations
-ligand substitution reaction
-Reaction and observations when ammonia added drop-wise
- [Cr(H2O)6]3+ takes part in a ligand substitution with an excess of aqueous ammonia forming the complex ion:
- [Cr(NH3)6]3+
- Added drop wise:
- When Ammonia added drop-wise to chromium(III) solution, the reaction takes place in two distinct steps
- Initially a grey-green precipitate of Cr(OH)3, is formed
- Cr(OH)3 precipitate dissolved in excess ammonia to form a complex ion:
- [Cr(NH3)6]3+
Equation is as follows:
Why is Carbon Monoxide toxic to haemoglobin?
- Haemoglobin contains Fe2+ groups that can carry oxygen
- Carbon monoxide can also bind to Fe2+ groups on haemoglobin molecules
- If breathed in, a ligand substitution reaction takes place
- Oxygen in haemoglobin is replaced by carbon monoxide
- To form carboxyhaemoglobin
- Carbon monoxide is bonded more strongly than oxygen
- Small conc. of CO in lungs prevents a large proportion of haemoglobin carrying O2
- Bond is so strong that the process is irreversible
- If conc. of carboxyhaemoglobin is too high, oxygen transport is prevented, leading to death
How does a precipitation reaction occur?
When two aqueous solutions contains ions react together to form an insoluble ionic solid - this is the precipitate
Precipitation reactions with NaOH
H
Reactions of copper ions in NaOH and NH3
NaOH:
Blue sol. → Blue ppt.
Insoluble in excess NaOH
-Equation:
NH3: Blue sol. —> blue ppt. then deep blue sol. Soluble in excess NH3 -Equation: Forms [Cu(NH3)4(H2O)2)2+ (aq)
Reactions and observations of Fe2+ ions with NaOH and NH3
Give equations for the reactions
NaOH:
Pale green sol. to green ppt.
Insoluble in excess NaOH
Ppt. turns brown - if exposed to air
NH3:
Pale green Sol. —> green ppt.
Insoluble in excess NH3
Reactions of Fe3+ ions with NaOH and NH3
NaOH:
Pale yellow Sol. —> orange/brown Ppt.
• Insoluble in excess NaOH
NH3:
Pale yellow sol. —> orange/brown Ppt.
Insoluble in excess NH3
Reactions of Mn2+ ions with NaOH and NH3
NaOH:
Pale pink sol. to light brown Ppt.
Insoluble in excess NaOH
NH3:
-Pale pink sol. —> light brown ppt.
• Insoluble in excess NH3
Reactions of Cr2+ ions with NaOH and NH3
NaOH:
-Violet sol. —> grey ppt.
Soluble in excess NaOH to form green solution
NH3:
• Violet sol. —> grey Ppt .
° soluble in ✗ CS Ntlz
↳ dissolves to form purple sol.
Red blood cells contain haemoglobin. Explain using ligand substitutions: - how haemoglobin transports oxygen around the body - why carbon monoxide is toxic (3 Marks)
- CO forms coordinate/dative bonds with Fe2+ central ion
- O2 is replaced by carbon monoxide
- CO forms stronger coordinate bonds than O2
- CO bonds irreversibly
- Prevents O2 from rebonding to haemoglobin ligand
2 metals that are not transition metals
- why?
- Zinc - full d-subshell
- Scandium - no electrons in d-subshell
- natural ions that form don’t contain incomplete d-subshells
Examples of transition metals as catalysts
Haber process - Fe2+
Contact process - Vanadium Oxide
Hydrogenation of alkenes - nickel
Decomposition of hydrogen peroxide - Manganese oxide
Reaction of zinc with acids - Cu2+
Catalytic converters - platinum, palladium, rhodium etc.
Transition elements ligand substitution table - learn or draw out and repeat
Most d-block elements are classified as transition elements.
Explain why scandium and zinc are classified as d-block elements but are not also transition elements.
Your explanations should include full electron configurations.
(4 Marks)
Transition elements are elements that form a stable ion with an incomplete d-sub shell
D-block element def - an element with its highest energy electron on a d-sub shell
e- configurations of stable ions:
Zn2+ -
Sc3+ -
Sc3+ loses all its 4s electrons and it’s all 3d electrons - empty 3d sub shell
Zn2+ loses all its 4s electrons, but contains a full 3d sub shell
