Chapter 24 Flashcards
What are transition metals?
Elements with an incomplete d-subshell that can form at least one stable ion with an incomplete d-subshell.
What two elements aren’t transition elements?
Scandium and Zinc.
Scandium only forms the ion Sc3+, configuration [Ar] 3d0
Zinc only forms the ion Zn2+, configuration [Ar] 3d10
What fills or loses electrons first? 3d or 4s?
4s
When writing them which is first 3d or 4s?
3d, 4s is always at the end.
What is the electron configuration of Chromium?
Cr is [Ar] 3d5 4s1 not [Ar] 3d4 4s2
this is because its energetically more stable.
What is the electron configuration of Copper?
Cu is [Ar] 3d10 4s1 not [Ar] 3d9 4s2
this is because its energetically more stable.
What are some general properties of transition elements?
-Variable oxidation states
-Form complex ions
-Form coloured compounds
-Behave as catalysts
What is a complex ion?
A molecule or ion, consisting of a central metal atom or ion, with a number of molecules or ions surrounding it
What is a ligand?
A ligand is a molecule or ion that forms a co-ordinate bond with a transition metal by donating a pair of electrons to the bond.
A molecule or ion surrounding the central metal atom or ion.
What colour is Cr3+
Green
What colour is Cr 6+
Orange/yellow
What colour is Mn2+
Pink
What colour is Cu2+
Blue
Why are transition metals good catalysts? How do they work?
Since transition elements can have variable oxidation states, they make excellent catalysts.
During catalysis, the transition element can change to various oxidation states by gaining electrons or donating electrons from reagents within the reaction.
Substances can also be adsorbed onto their surface and activated in the process.
Examples of how transition metals are used as catalysts in industrial processes:
1- Haber process to manufacture ammonia. Catalysed by finely divided iron catalyst.
2- Contact process, producing sulphur triode. Catalysed by vanadium oxide (V2O5)
3- catalytic decomposition of hydrogen peroxide uses manganese (V1) oxide as the catalyst.
Is a ligand like a nucleophile or electrophile?
Nucleophile
ligands have a negative charge or a lone pair of electrons capable of being donated
What is the Co-ordination number?
number of co-ordinate bonds to the central metal atom or ion.
What are Monodentate ligands? give some examples
can form only one dative bond to the central metal ion.
eg. H20, NH3, CL-,CN-
What are Bidentate ligands? Give some examples
can each form two dative bonds to the central metal ion, as each ligand contains 2 atoms with a lone pair.
eg. 1,2-diaminoethane (H2NCH2CH2NH2) which is also written as ‘en’ or Ethanedioate ion (C2O42- ) which is sometimes written as ‘ox’
How many coordinate bonds are present in an octahedral complex?
six coordinate bonds
could be 6 monodentate bonds or 3 bidentate ligands.
How many coordinate bonds are present in a tetrahedral shape?
4 coordinate bonds.
How many coordinate bonds are present in a square planar?
4 coordinate bonds.
this is used instead of the tetrahedral most commonly when platinum is the central ion. (When the transition metal have 8 d-electrons in the highest energy d sub shell)
How many coordinate bonds are present in a square planar?
4 coordinate bonds.
this is used instead of the tetrahedral most commonly when platinum is the central ion. (When the transition metal have 8 d-electrons in the highest energy d sub shell)
What is cis isomerism?
Same side
What is trans isomerism?
opposite sides
What is optical isomerism?
the two forms are non-superimposable mirror images of each other. They have no plane of symmetry, and one image cannot be placed directly on top of the other.
They are mirror images of each other.
What is cis-platin?
A drug used to treat cancer in chemotherapy.
How does cis-platin work?
The cis-platin works by binding to the nitrogen atoms on the bases in DNA
The cis-platin passes through the cell membrane and undergoes ligand exchange where the chlorines are replaced by water molecules
The nitrogen is a better ligand than water and forms dative covalent bonds with the cis-platin
The cis-platin distorts the shape of the DNA and prevents the DNA from replicating
In short- it forms a platinum complex inside a cell which binds to DNA and prevents the DNA from replicating.
Weaknesses to using cis-platin to fight cancer..?
Cis-platin binds to healthy cells as well as cancerous cells, but affects cancer cells more as they are replicating faster. Unfortunately, this means that other healthy cells which replicate quickly, such as hair follicles, are also affected by cis-platin.
What is ligand substitution?
one ligand in a complex is replaced by another.
It forms a new complex that is more stable.
Explain the substitution with copper II complexes in water with NaOH and NH3..
The [Cu(H2O)6]2+ (aq) complex ion is blue in colour.
Upon dropwise addition of sodium hydroxide (NaOH) solution, a light blue precipitate is formed.
Partial ligand substitution of two water ligands by two hydroxide ligands has occurred.
Upon addition of excess concentrated ammonia (NH3) solution, the pale blue precipitate dissolves to form a deep blue solution.
Partial ligand substitution has occurred and [Cu(NH3)4(H2O)2] is formed.
What would happen if concentrated ammonia was added dropwise to [Cu(H2O)6] instead of NaOH?
The same light blue precipitate would have formed, and it will dissolve to form a dark blue solution if excess ammonia is added.
Explain the substitution with copper II complexes in water with concentrated HCL..
The water ligands in [Cu(H2O)6]2+ can also be substituted by chloride ligands.
This forms [Cu(Cl)4]. There is a change in coordination number as the chloride ligands are larger in size so fewer fit around the central Cu2+ ion.
the blue solution turns yellow. With an intermediate of green due to the yellow and blue mixing
If you add water this will reverse.
Explain the substitution with chromium II complexes in water with NaOH and NH3..
When chromium III potassium sulphate (KCr(SO4)2 12H2) is dissolved in water it forms [Cr(H20)6]. This is a pale purple solution.
When chromium III sulphate is dissolved in water its a green solution of [Cr(H2O)5SO4]+. One ligand of H2O has been replace.
When ammonia is added drop-wise to [Cr(H20)6] it first creates a grey-green precipitate of Cr(OH)3.
This precipitate dissolves in excess ammonia to form [Cr(NH3)6]3+ and it becomes purple.
How does ligand substitution in haemoglobin work? (oxygen and carbon monoxide)
The haem molecule is a complex with iron(II) at its centre, Oxygen atoms form a dative covalent bond with the Fe(II) which enables oxygen molecules to be transported around the body in the blood.
Oxygen molecules are not very good ligands and bond weakly to the iron(II). The weak bonds allows them to break off easily and be transported into cells. (forms oxyhemoglobin).
Carbon monoxide is toxic because it is a better ligand than oxygen and binds strongly and irreversibly to the iron(II) preventing oxygen from being carried to the cells.
