transition elements Flashcards
what type of element are the transition elements
metals - meaning they all have metallic properties
transition element definition
d-block elements that form at least 1 ion with a partially filled d orbital
what are the 2 d-block elements that are not classified as transition elements
Sc and Zn
these elements only form Sc3+ and Zn2+ which empties/fills d sub shells
they are just d-block elements
which 2 transition elements have exceptional electron configurations
Cr and Cu
their configurations should end in 3d4 4s2 and 3d9 4s2 respectively, but 3d4 and 3d9 are very unstable as they are so close to 3d5 and 3d10, which are much more stable arrangements
so their electron configurations become 3d5 4s1 and 3d10 4s1
- both still transition metals !
4 properties of transition elements + examples
- multiple oxidation states
- they form coloured compounds
- the elements and their compounds can act as catalysts
- they can form complex ions
e.g. iron (ii) which is pale green and iron (iii) which is brown-yellow, iron is a catalyst for the haber process
remember they also have the same properties as normal metals
complex ion definition
a central metal ion with 1 or more molecules or charged ions bound to it by dative covalent bonds
usually formed by d-block elements - not all of them e.g. not Zn - but can also be formed by other elements e.g. Al
ligand definition
a molecule/atom/ion that donates a pair of electrons to a central metal atom by dative covalent bonding - it must have a lone pair
what are the 2 types of ligands + examples for each
neutral e.g. H2O, NH3
charged e.g. CN- , OH-, halide ions
coordinate number definition
the number of dative bonds made to the central metal ion
- not = to number of ligands
monodentate ligand definition
a molecule/atom/ion which can form 1 dative bond by donating 1 lone pair
bidentate ligand definition
a molecule/atom/ion which can form 2 dative bonds by donating 2 lone pairs
polydentate ligand definition
a molecule/atom/ion which can form more than 2 dative bonds by donating more than 2 lone pair
what shape would a complex ion with a coordinate number of 6 be
octahedral
what shapes could a complex ion with a coordinate number of 4 be
tetrahedral
square planar
what is the bond angle in a square planar
90°
what type of complex is [x(H2O)6]
… hexaaqua
what shape are hexaaqua complexes normally
octahedral
what type of complex is [xCl4]
… tetrachloro
what shape are tetrachloro complexes normally
tetrahedral
what type of transition elements tend to form square planars + 3 examples
transition metals with 8d electrons
e.g. platinum (II), gold (III)
give 2 examples of bidentate ligands
1,2 - diaminoethane
H2N-CH2-CH2-NH2
ethandioate (a dicarboxylate ion)
-OOC-COO-
optical isomerism definition
molecules with the same molecular formula but are nonsuperimposable mirror images of each other
what 3 types of complex ions can display cis-trans isomerism
- square planar complexes with 2 identical ligands (not more) - cis=adjacent, trans=opposite
- octahedral complexes with 4 of one ligand and 2 of another - cis=adjacent, trans=opposite
- octahedral complexes with 2 monodentate and 2 bidentate ligands - cis=adjacent, trans=opposite
what type of complex ion can display optical isomerism
a complex ion with 2 or more bidentate ligands
outline the role of cis-trans isomerism in complex ions in medicine (cis-platin)
- cis-platin is a complex ion with the formula [Pt(NH3)2Cl2]
- it is able to form a platinum complex inside a cell which binds to DNA, preventing DNA replication and therefore mitosis
- activation of the cells own repair system then leads to apoptosis
- it has been used in chemotherapy as it can attack tumours, even causing them to shrink in size
- there are some unpleasant side effects however, many of which lead to kidney damage
what effect does adding NH3 or NaOH have on aq transition metal complexes
it causes the formation of coloured precipitates of the insoluble transition metal hydroxides
- this is because they both dissociate in aq solution to form a supply of OH-
- the precipitates can then be redissolved by adding acid
ligand exchange/substitution definition
a reaction when ligands in a complex ion are swapped for another
- this often causes a colour change
what happens to metal complexes in ligand substitution reactions with similarly sizes + uncharged ligands
coordinate number and shape will not change
what happens to metal complexes in ligand substitution reactions from small uncharged to larger charged ligands or vice versa
the coordinate number and shape will change
give the formula + colours for Cr3+ as:
- metal-aqua ion
- with OH-
- with excess OH-
- with NH3
- with excess NH3
metal-aqua ion
[Cr(H2O)6]3+ - violet solution
with OH-
Cr(OH)3(H2O)3 - grey- green precipitate
with excess OH-
[Cr(OH)6]3- - dark green solution
with NH3
Cr(OH)3(H2O)3 - grey-green precipitate
with excess NH3
[Cr(NH3)6]3+ - purple solution
give the formula + colours for Fe2+ as:
- metal-aqua ion
- with OH-
- with excess OH-
- with NH3
- with excess NH3
metal-aqua ion
[Fe(H2O)6]2+ - pale green solution
with OH-
Fe(OH)2(H2O)4 - green precipitate, turns brown on the surface over time
with excess OH-
no change - doesn’t react so stays as insoluble precipitate
with NH3
Fe(OH)2(H2O)4 - green precipitate, turns brown on the surface over time
with excess NH3
no change - doesn’t react so stays as insoluble precipitate
give the formula + colours for Fe3+ as:
- metal-aqua ion
- with OH-
- with excess OH-
- with NH3
- with excess NH3
metal-aqua ion
[Fe(H2O)6]3+ - pale yellow solution
with OH-
Fe(OH)3(H2O)3 - orange-brown precipitate
with excess OH-
no change - doesn’t react so stays as insoluble precipitate
with NH3
Fe(OH)3(H2O)3 - orange-brown precipitate
with excess NH3
no change - doesn’t react so stays as insoluble precipitate
give the formula + colours for Mn2+ as:
- metal-aqua ion
- with OH-
- with excess OH-
- with NH3
- with excess NH3
metal-aqua ion
[Mn(H2O)6]2+ - pink solution
with OH-
Mn(OH)2(H2O)4 - pale brown precipitate
with excess OH-
no change - doesn’t react so stays as insoluble precipitate
with NH3
Mn(OH)2(H2O)4 - pale brown precipitate
with excess NH3
no change - doesn’t react so stays as insoluble precipitate
give the formula + colours for Cu2+ as:
- metal-aqua ion
- with Cl-
- with OH-
- with excess OH-
- with NH3
- with excess NH3
metal-aqua ion
[Cu(H2O)6]2+ - blue solution
with Cl-
[CuCl4]2- - yellow solution
with OH-
Cu(OH)2(H2O)4 - blue precipitate
with excess OH-
no change - doesn’t react so stays as insoluble precipitate
with NH3
Cu(OH)2(H2O)4 - blue precipitate
with excess NH3
[Cu(NH3)4(H2O)2]2+ - dark blue precipitate
- only a partial substitution occurs here
why are metal-aqua ions the same colour as the lone transition metal ion
this is because H2O is an uncharged ligand, meaning that the oxidation state is the same as its lone ion, so the colour is the same
why is there sometimes a colour change between reacting a transition metal ion with NH3 and excess NH3
this is because the NH3 doesn’t get substituted unless it’s in excess, it just provides a source of OH-
- the reaction with OH- changes the oxidation state so there is usually a colour change
when the NH3 does get substituted, as NH3 is an uncharged ligand, the oxidation state reverts back to its normal oxidation state, causing a colour change, although it doesn’t change back to the same colour it is as a lone ion
- this doesn’t occur for all transition metal ions, as some do not react with excess NH3 at all
outline how 2 different transition metal ions can be identified
add NH3 or NaOH and the ions will form coloured precipitates
why does the precipitate Fe(OH)2 often turn orange-brown on the surface when left standing
this is because the Fe2+ gets oxidised to Fe3+ in the air, and Fe(OH)3 is an orange-brown colour
give an example of a complex metal ion in the body
haemoglobin
- it consists of a central Fe2+ metal ion with a multidentate haem ring containing 4 nitrogens that form 4 dative bonds in a square planar configuration
- the Fe2+ ion forms one other dative bond with the rest of the protein
- this leaves 1 last spot allowing O2 to reversibly bond with the central Fe2+ ion, allowing it to be carried around the body
- this forms oxyhaemoglobin
why is CO dangerous in terms of ligand exchange
CO has a lone pair of electrons therefore it can act as a ligand, and it forms a much stronger dative bond with Fe2+ than O2
- if CO is present, it can replace via ligand exchange to form carboxyhaemoglobin
what occurs in a reaction between Fe2+ and MnO4-
Fe2+ is oxidised to Fe3+
MnO4- is reduced to Mn2+
- causes a purple to colourless colour change
what occurs in a reaction between Fe3+ and I-
Fe3+ is reduced to Fe2+
I- is oxidised to I2
- causes a colourless to brown colour change - overpowers the iron colour change
what occurs in a reaction between Cr2O7 2- and Zn
Zn is oxidised to Zn2+
Cr2O7 2- is reduced to Cr3+
- this causes an orange to green colour change
in excess of Zn this can be further reduced to Cr2+ which is pale blue
what occurs in a reaction between Cr3+ and hot H2O2
Cr3+ is oxidised to CrO4 2-
- this causes a green to yellow colour change
O is reduced in H2O2 to CrO4 2-
what occurs in a reaction between Cu2+ and I-
Cu2+ is reduced to Cu+, which then forms CuI
- this causes a change form a pale blue solution to a white precipitate (CuI)
I- is oxidised to I2
- this causes a colour change from colourless to brown - mostly this is what is observed
what occurs in the reaction between hot Cu2O and H2SO4 + what type of reaction is it
Cu is reduced from Cu2O to Cu
- this forms a brown solid
Cu is also oxidised from Cu2O to CuSO4
- this forms a blue solution
this is a disproportionation reaction
what type of reaction forms a precipitate
precipitation reaction
what occurs in a reaction between CrO4 2- and acid
CrO4 2- will turn into Cr2O7 2- (oxidation state stays the same)
