Transition Metals - substitution reactions (some drawings on paper flashcards to refer to!!)
what is a complex ion
a complex ion is where a central transition metal ion is surrounded by ligands bonded by dative covalent (coordinate) bonds
what is a ligand
an atom, ion or molecule with at least 1 lone pair of electrons that it can donate to the central metal ion.
what is a coordinate/datvie covalent bond
when both electrons of a shared pair come from the same atom.
what is the co-ordination number
the nuimber of co-ordinate bonds formed to the central ion. NOT THE NUMBER OF LIGANDS
what are the thre types of ligands
monodentates, bidentates and polydentates.
what are monodentates
also known as unidentates and they are ligands with only one lone pair of electrons. eg - H20:
- :NH3
- :Cl^-
why is water monodentate even tho it has 2 lone pairs of electrons
the 2 lone pairs are so close together thast they can only form one co-ordinate bond
whats similar about the :NH3 and the H2O: ligands
they are similar in size and are uncharged.
the ligand substitution reaction of the ligands :NH3 and the H2O: occurs without the changhe of the co-ordination number.
what happens in the Ligand substitution of :NH3 and the H2O:. and give and exmaple.
the ligand substitution reaction of the ligands :NH3 and the H2O: occurs without the changhe of the co-ordination number. eg -
[Co(H2O)6]^2+(aq) + 6NH3 (aq) -> [Co(NH3)6]^2+(aq) + 6H2O (l)
- Here the Co has an os of 2+ in both parts of the reaction (with water and ammonia ligands) and the shape remains octaheadral.
what is an incomplete ligand substitution reaction
where only some of the original ligands have been replaced. it occurs when the partially substituted is energetically more stable than either the original complex or the completely substituted complex.
give the equation of [Cu(H2O)6]^2+ with ecxess ammonia in an incomplete ligand substitution reaction.
when [Cu(H2O)6]^2+ reacts with excess ammonia =
[Cu(H2O)6]^2+(aq) + 4NH3 (aq) => [Cu(NH3)4(H2O)2]^2+(aq) + 4H2O (l)
- the Cu becomes [Cu(NH3)4(H2O)2]^2+ which forms a deep blue solution from being blue.
where do the chloride ions come from for the ligand substitution reaction with an aquesous ion.
from conc HCl or saturated NaCl.
what happens to the co-ordination number and the shape when conc HCl is added to aqueous ions of Cu -> [Cu(H2O)6]^2+ and Co -> [Co(H2O)6]^2+
- what happens when [Fe(H2O)6]3+ is added to Cl- ligands
they change in coordination number from 6 to 4.
- eg - with aqueous copper ions = [CuCl4]2- is formed and the colour changes from pink to yellow/green solution
- eg - with the cobalt aquaous ion = [CoCl4]2- is formed and the colour changes from blue to a yellow solution.
- they both go from being octahedral to tetraheadral in shape.
- [Fe(H2O)6]3+ + 4Cl - =>[FeCl4]^- + 6H2O
here both solutions stay yellow but like the others the shape changes from being octaheadral to tetraheadral.
how is the Cl- ligand different to the uncharged H20 and the NH3 ligands and how
the Cl- ligand is charged and larger than the other uncharged ligands (H20 & NH3).this means only 4 Cl- ion ligands can fit around so this ligand exchange involves a change of co-ordination number and shape.
what happens If solid copper chloride (or any other metal) is dissolved in water
it forms the aqueous s [Cu(H2O)6]2+ complex and not the chloride [CuCl4]2- complex.
what are bidente ligands,
and give examples (structures drawn on paper flashcards)
ligands with 2 atoms -with 2 lone pairs - so can form 2 co-ordinate bonds per ligand.
eg - NH2CH2CH2NH2 =ethan-1-2-diamine and ethanedioate ion C2O42-
what happens in the reaction when a dilute aqueous solution containing ethanedioate ions is added to a solution containing aqueous copper(II) ions.
a partial substitution reaction, the four water molecules are replaced and new complex is formed.
[Cu(H2O)6]2+ + 2C2O42- => [Cu(C2O4)2(H2O)2]2-+ 4H2O
give an exmaple of a
multidente ligand, and how many coordinate bonds can it form
- EDTA^4-
this can form 6 coordinate bonds per ligand - heam is another multidentate ligand.
what is a multidentate
they are ligands that have more than 1 coordinate bond.
what is heam
the multidentate ligand found in a molecule of heamoglobin. with 4 coordinate bonds from nitrogen to the iron.
what is heamoglobin
a protein that transports oxygen aroun the body in the blood.
what structure does heamoglobin have (more on the paper flashcard
octaheadral
what happens with the oxygen and heamoglobin in the lungs
in the lungs there is a high concentration of oxygen. so the oxygen substitutes the H2O ligand on heamoglobin to form oxyheamoglobin. this is then trasnported around the body where needed.
what happens with the heamoglobin around the body.
- oxyheamoglobin gives up it’s oxygen to where it’s needed like respiring muscles and picks up the water (thats released by respiration).
- so water has substituted oxygen and the heamoglobin returns to the lungs where the water is breathed out as water vapour.
- new oxygen is taken in to start the process again.
what effects does carbon monoxide have on health
it is a poisoonous gas, that causes headaches, unconsciousness and even death. it is known as the silent killer.
what happens when Co is inhaled
the CO ligand replaces the water ligand on heamoglobin. the problem is that it bonds vary strongly to the iron and isn’t readily replaced by oxygen or water. so oxygen can’t be transported around the body and leads to oxygen starvation in organs = CO is poinsonous.
how many small monodentate ligands (like :H2O & :NH3) can you fit around a central metal ion
6 of the small ligands
How many large monodentate ligands (like :Cl-) can you fit around a metal ion
4 of the large ligands
How many bidentate ligands (like enthandioate and ethane-1-2-diamine) can you fit around a metal ion
3 of these ligands.
what shape do complexes with a coordination number of 6 form and give an example
octaheadral shapes with a bond angle of 90 degrees
- eg = [Co(H2O)6]^2+
what shapes do complexes with a coordination number of 4 form, and give an example of each shape
- tetraheadral shapes with a bond angle 109.5 degrees = [cuCl4^-]2-
- square planar with a bond angle of 90 degree. = Pt[NH3)2(Cl)2] = cis-platin
what shapes do complexes with a coordination number of 2 form and give an example
linear shapes with a bond angle of 180 degress. = [Ag(NH3)2]+ = tollens reagent (differentiates between ketones and aldehydes.
what is the equation to find the total oxidation state of metal
total OS of a metal = total oxidation state - total OS of ligands.
Give an example of a nonodentate ion ligand that forms stronger bonds that H2O, and what does this strong bond result in.
CN- forms stronger bonds, so the reaction isnt easily reversed and the new complex formed is more stable.
what ligands forms more stable complexes - multidnetate/bidentate or monodnetate
multidentate/bidentate ligands = more stable complexes. = reaction harder to reverse.
recap - what is entropy
the mesaure of disorder in particles in 1 mole of a substance - the number of ways paticles in atoms or molecules can be rearranged.
state how entropy be applied to stability of complexes formed in ligand substitution
increase in entropy = more stable complexes.
comment on the Enthalpy change (/_\H) in ligand substitution reactions
ligand substituion reactions usually result in the bonds in reactants being broken and the new bonds in the products being formed, usually the energy needed to break the bonds is similar as the enrgy released when the bonds are formed again resulting in a small enthalpy change. (or a negative enthalpy change)
other than the small enthalpy change, what factor influences the stability of complexes formed.
the entropy
define the chatale effect
the substitution of monodentate ligands with a bidentate or multidentate ligand leads to a more stable complex. it also results in the complex solution created having more particles in it, meaning the entropy increases.
why is a reaction with a high entropy more likely to happen with a stable product being formed, use the example of the reaction between an aqua copper complexand EDTA4-
[Cu(H2O)6]^2+(aq) + EDTA4- (aq) -> [Cu(EDTA)]^2- (aq) + 6H2O (l)
its more likely to happen cos their are more moles on the products side (7) compared to 2 moles on the reactants side. this increases entropy = making it difficult to reverse as it is entropically favourable. (positive entropy change value)
- here the enthalpy change is small/close to zero as their are similar number of coordinate bonds in both complexes so same energy needed and released = (negative delta H value)
= overall the negative enthaly change and the positive entropy change = a negative free energy value (/_\G) = more favourable/likely to happen and the product formed being stable.
