Transition Elements Flashcards
Electron configuration Chromium (24)
1s2 2s2 2p6 3s2 3p6 3d5 4s1
Electron configuration Copper (29)
1s2 2s2 2p6 3s2 3p6 3d10 4s1
Properties of transition elements
- Coloured compounds
- Act as a catalyst
- Form complex ions/Ligand substitution
- Variable oxidation states
Colour of Co2+ in solution
Pink
Colour of Fe2+ in solution
Pale green
Colour of Fe3+ in solution
Yellow
Colour of Cu2+ in solution
Blue
Colour of Co2+ complex hydroxide precipitate and equation
Blue which turns beige in the presence of air
+ 2OH- -> (H2O)4(OH)2 + 2H2O
Colour of Fe2+ hydroxide precipitate and equation
Green, then turns brick red in presence of O2
Colour of Fe3+ hydroxide precipitate and equation
Brick red/ rusty brown
Colour of Cu2+ hydroxide precipitate and equation
Blue
What is a bidentate ligand?
A ligand which can donate two lone pairs of electrons to the central metal ion to form coordinate bonds
Ligand substitution in complexes:
Cu 2+ and ammonia, first a small amount then in excess
A small amount: pale blue precip. of Cu(OH)2
Excess: precip. dissolves, deep blue solution + 4NH3 [Cu(NH3)4(H2O)2]2+ + 4H2O
Cu 2+ and hydrochloric acid
Initially turns green then yellow solution
+ 4Cl- equil. [CuCl4]2- + 6H2O
Co 2+ and conc. hydrochloric acid
Dark blue solution
+ 4Cl- equil. [CoCl4]2- + 6H2O
Co 2+ and ammonia
Small amount: = 2NH3 -> (H2O)4(OH)2 + 2NH4+ green precip
Excess: start from same complex ion, + 6NH3 -> []6NH3 2+ + 6H2O beige then black on standing
What is a transition element?
A d block element that forms an ion with an incomplete in d sub-shell.
Why does 4s sub shell fill before 3d sub-shell and which electrons are lost first?
Has a lower energy. 4s electrons are lost first
Explanation for unusual electron config.s of chromium and copper
More energetically favorable arrangement as lower energy so more stable.
Transition metal uses
Nickel alloyed w. copper for making silver coins, titanium in joint replacement parts, iron alloyed for construction
Trend in atomic radii and IE
Little variation as electrons are added to inner 3d sub-shell not outer 4s sub-shell which affects atomic radii. Nuclear charge increases but IE doesn’t increase by much due to pretty much same shielding and atomic radii
Why are they denser than s block elements?
Smaller ions. Strong bonding between them pulling them close together, greater masses.
Why high melting point?
More delocalisable electrons - greater ion charge
Why variable oxidation states?
They have a number of electrons with similar ionisation energies.
How act as catalyst?
Provide a surface for reaction to take place on. Reactants adsorbed, products desorbed.
Ability to gain or lose electrons means that they can bind to reactants forming an intermediate as part of a chemical pathway with a lower activation energy
Example of transition metals as catalysts
Iron metal in haber process
V2O5 in contact process
Nickel in hydrogenation of alkenes
MnO2 in decomp. of hydrogen peroxide
How and why coloured compounds?
Need to have partially filled d sub-shells (promote d electrons from lower energy levels to higher energy levels, requiring electrons to be promoted and spaces to promote them into). Colour observed is mixture of wavelengths not absorbed.
What is a complex ion?
A transition metal ion bonded to one or more ligands by coordinate bonds
What is a coordinate bond?
Bond in which both electrons in shared pair are donated by the same bonding atom
What is a ligand?
A molecule or ion which donates a pair of electrons to the central metal ion to form a coordinate bond
What is coordination number?
The total number of coordinate bonds formed between a central metal ion and its ligands
Why do transition metal ions form complex ions?
They are relatively small and have two or more charges, therefore their high charge density makes them strongly polarizing and able to attract lone pairs of electrons or ions on molecules
Requirement to act as a ligand
At least one lone pair of electrons
Formula and charges of following ligands:
- Water
- Ammonia
- Thiocyanate
- Cyanide
- Chloride
- Hydroxide
- :OH2 & neutral
- :NH3 & neutral
- :SCN- & -1
- :CN- & -1
- :Cl- & -1
- :OH- & -1
What is a monodentate ligand?
A ligand that donates just one pair of electrons to the central metal ion to form one coordinate bond
Using VSEPR, describe how coordination number influences the shape of complex ions
Electron pairs repel each other, coordinate bonds are bonding electron pairs which will repel each other equally and as far apart as possible to minimize repulsion. Thus, number of coordinate bonds will influence the shape of the complex ion
What type of complex ions does cis/trans isomerism occur in?
Octahedral complex ions that contain four of one type of ligand and two of another
Square planar complex ions
Difference between cis and trans complex ion isomers
In the cis, the two ligands which are the same are at adjacent corners and 90~ to one another
In the trans, the two ligands which are the same are at opposite corners and 180~ to one another
What is a bidentate ligand?
A ligand that can donate two lone pairs of electrons to the central metal ion to form two coordinate bonds.
What is a hexadentate ligand?
A ligand with 6 lone pairs of electrons, each forming a coordinate bond to a metal ion in a complex ion
What is EDTA and its usual form in complex ions
EDTA 4-:
:N(:O-OCCH2)2 CH2CH2 N:(:O-OCCH2)2
EDTA has Hs attached to O-
What does EDTA do?
Binds metal ions and decreases the conc. of metal ions in solutions by binding them into a complex (as a chelating agent)
Uses of EDTA
In detergents, binds to calcium and magnesium to reduce the hardness of water
Uses in some foods as a stabilizer to remove metal ions that might catalyze the oxidation of the product
In medicine, added to blood samples to prevent clotting and used to treat patients with lead and mercury poisoning
Which complex ions form optical isomers?
Octahedral complexes that contain multidentate ligands
Requirements for optical isomers
(No plane of symmetry)
- A complex with three molecules or ions of a bidentate ligand
- A complex with two molecules or ions of a bidentate ligand, and two molecules or ions of a monodentate ligand
- A complex with one hexadentate ligand
What is a ligand substitution?
A reaction in which one ligand in a complex ion is replaced by another ligand
Reaction between copper (II) ions and ammonia
Small amount of ammonia: ammonia acts as base and blue precipitate of Cu(OH)2 is formed (from blue solution)
When excess ammonia is added, the pale blue precip dissolves and a deep blue solution is formed. Four of water ligands are replaced by ammonias.
[Cu(H2O)6]2+ + 4NH3 [Cu(NH3)4(H2O)2]2+ + 4H2O
Reaction between copper (II) ions and conc. HCl
Blue solution turns green then yellow. When green, both the blue and yellow, aqua and the chloro complexes are present.
[Cu(H2O)6]2+ + 4Cl- [CuCl4]2- + 6H2O
Cobalt (II) ions and conc. HCl
Pale pink solution turns dark blue.
[Co(H2O)6]2+ 4Cl- CoCl4 2- + 6H2O
Cobalt (II) ions and ammonia
Small amount: Green precip of hydroxide
Excess: Straw coloured solution is formed
[Co(H2O)6]2+ + 6NH3 [Co(NH3)6]2+ + H2O
Test for iron (III) ions using SCN-
[Fe(H2O)6]3+ + SCN- [Fe(SCN)(H2O)5]2+ + H2O
Yellow/orange solution turns deep blood red
What is the equation for Kstab?
[new complex]/[aqua complex][new ligands]^no. of moles of ligand in eqn.
What does large Kstab value show about equilibrium?
The position of equilibrium lies to the right
What does a large Kstab value show about stability and formation of ion?
Complex ions with larger Kstab values are more stable than those with lower ones, large stability shows that the ion is easily formed
What is structure of cis-platin?
Square planar, Pt at centre, 2 NH3, 2 Cl
What is use of cis-platin?
Treatment of cancer
How does cis-platin work?
Binds onto the DNA of cancerous cells, preventing division and ultimately triggering cell death
Problems with cis-platin?
Unpleasant side effects
Cis-platin ligand sub.
A Cl is subbed for water which can subsequently be lost and cis-platin binds to DNA
What is carboplatin and what is its advantage?
Fewer side effects and lower doses. Cl s in cis-platin replaced by bidentate structure.
What is haemoglobin?
A complex protein composed of four polypeptide chains.
Characteristic of haem groups?
Fe2+ ion in at centre
How does haemoglobin work?
Oxygen binds to Fe2+ ion, as blood passes through the lungs, the haemoglobin picks up oxygen and carries it to the cells to be released. CO2 can be picked up and taken to lungs
Structure of coordinate bonds formed around Fe2+ in haem group
4 N: groups in corners of parallelogram, globin and O2
What is it that allows CO, H2O and O2 to bind to Fe2+ ?
Lone pairs of electrons
Haemoglobin sub.
H2O replaced by O2
CO problem
Binds more strongly than oxygen (much higher Kstab). Substitution is irreversible. Starves respiring tissues of oxygen
What to talk about with altitude
Equilibrium with haemoglobin oxygen ligand sub.
