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Flashcards in Transition Elements Deck (68):

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



Colour of Fe2+ in solution

Pale green


Colour of Fe3+ in solution



Colour of Cu2+ in solution



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



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:
1. Water
2. Ammonia
3. Thiocyanate
4. Cyanide
5. Chloride
6. Hydroxide

1. :OH2 & neutral
2. :NH3 & neutral
3. :SCN- & -1
4. :CN- & -1
5. :Cl- & -1
6. :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.