Transition metals Flashcards
definition of transition metal
a transition metal that forms at least one stable ion with partially filled d orbitals
What are the 2 exceptions of the d block that aren’t transition metals
scandium and zinc
Why are Sn and Zn still d block elements even though they aren’t transition metals
They have their highest energy electron in the d orbitals
What is the electron config of Chromium
1s2 2s2 2p6 3s2 3p6 4s2 3d5
What is the electron config of Copper
1s2 2s2 2p6 3s2 3p6 4s2 3d10
why is scandium not a transition metal
It only forms the ion Sn3+ and loses its 4s electrons and 3d1, so no partially filled d orbitals
why is zinc not a transition metal
it loses its 4s electrons to form Zn2+ only, so no partially filled d orbitals
what is the electronic config for Cr3+
[Ar] 3d3
what is the electronic config for Mn4+
[Ar] 3d3
what is the electron configuration for Fe2+
[Ar] 3d6
what is the electronic config for Fe3+
[Ar] 3d5
what is the electronic config for Cu2+
[Ar] 3d9
The common oxidation numbers of chromium are 2+, 3+ and 6+ .
Give reasons in terms of oxidation energies why chromium can show variable oxidation numbers. 1 mark
Its successive ionisation energies are similar
what is the co-ordination number if a complex ion
how many dative bonds that exist in a complex ion
what is the co ordination number pf [Co(NH3)6]3+
6
where do the electrons go when dative bonds are made in complex ions
empty available d orbitals
What is the coordination number and transition metal oxidation state off [Fe(H2O)6]3+
ox state: 3+, coord: 6
explain why a complex ion with 2 ligands would be linear
2 bonding pairs, no lone pairs, electron pairs spread out as far as possible to minimise repulsion, so the bond angle is 180 and the shape is linear
explain why Cu2+ ions will accept 6 water molecules as ligands, but only 4 chloride ions as ligands
- Cl-ions are negative and so will repel each other
- H2O molecules are neutral and have no charge
- Cl- in general is much bigger than a H2O molecule, so physically cannot fit more Cl- around the Cu2+
Some complexes with 4 ligands will be tetrahedral,while others might be square planar. Why?
the transition metal has lone pairs in a square planar shape
What is a monodentate ligand
A monodentate ligand is a species that is only able to form one co-ordinate bond to a transition metal ion.
What is a bidentate ligand
A bidentate ligand is a species that is able to form two co-ordinate bonds to a transition metal ion.
Whats a multidentate ligand
A multidentate ligand is able to form multiple (2 or more) co-ordinate bonds to a transition metal ion
draw out 3 ethanedioate molecules acting as ligands around a Cu2+ metal ion
compare to notes
What shape must all cis-trans isomers be and why
square planar, if they are tetrahedral then species that are the same end up being next to each other, as hence do not show cis-trans isomerism
definition of cis-trans isomerism
where molecules have the same chemical formula but different spatial arrangements of atoms, specifically when identical groups are positioned on the same side of a double bond or ring in a “cis” isomer, and on opposite sides in a “trans” isomer
a complex ion contains one Fe3+ion, four ammonia molecules and two chloride ions
Draw out the cis trans isomers of this complex ion
[Fe(NH3)4(Cl2)]+1
Compare to notes
When transition metals make ions, why does the 4s subshell leave first as opposed to the 3d subshell
4s subshell is further from the nucleus than 3d
what occurs in ligand exchange
- pH change
- ligand exchange if a better ligand is available (makes a stronger bonds with the transition metal ion)
- change in co ordination number, leading to an increase in S (entropy)
what is the chelate effect
where ligand exchange occurs from multiple monodentate ligands to multidentate ligands
an example is
[Cu(H2O)6]2+(aq) + EDTA4-(aq) –>[CuEDTA]2-(aq) + 6H2O(l)
this is driven by entropy increase
what is the chelate effect driven by and explain what it is
entropy increase
e.g going from 2 aqueous species to 7 massively increases entropy, so is thermodynamically favourable
a positive entropy change is favourable as we create a more stable complex ion, therefore making it more favourable to have more moles on the right of the equation than on the left
This is achieved by the substitution of multiple monodentate ligands for less multidentate ligands
if a transition metal ion has a high oxidation number, it tends to be a better …. agent
oxidising
if a transition metal ion has a low oxidation number, it tends to be a better …. agent
reducing
what does polyatomic mean
a group of two or more atoms that are covalently bonded and have a net charge
half equation for reduction of Cr2O72- –> Cr3+
Cr2O72- + 14H+ + 6e- –> 2Cr3+ + 7H2O
what is the reaction between aqua ligands (e.g. Cu(h2o)6 and OH- ions
the aqua ligand is removed of the equivalnet number of water molecules as moles of OH-, as the OH- rips off H+ ions off of the water attached to the metal ion.
This always forms a hydroxide precipitate
In this case, Cu(H2O)6 + 3OH- –> Cu(H2O)3(OH-)3(s) + 3H2O(l)
what happens if there is an excess of NaOH when reacting this with an aqua ligands that have already been reduced, such as Cr(H2O)3(OH)3
Cr(H2O)3(OH)3 reacts with the OH- ions to form [Cr(OH)6] + H2O (this equation that you have written isn’t balanced but doesn’t matter for now)
this reaction only happens in excess OH- and we can say that the precipitate ‘redissolves’ in excess
What happens when an aqua ligand reacts with ammonia and what is formed
The ammonia acts as both a base and a ligand. With a small amount of ammonia, hydrogen ions are pulled off the hexaaqua ion exactly as in the hydroxide ion case to give the same neutral complex.
e.g. [Cr(H2O)6]3+ + 3NH3 –> [Cr(H2O)3(OH)3] + 3NH4+
which two transition metals that we study do further ligand exchange with excess NH3 after the hydroxide ppts form
Copper and cobalt
which two transition metals do we study do ligand exchange with excess Cl-
copper and cobalt
write out an equation for ligand exchange of hexaaqua copper 2+ and 4Cl-
remember how many Cl- will fit around a transition metal
[Cu(H2O)6 ]2+ (aq) + 4Cl- (aq) –> [CuCl4]2-(aq) + 6H2O(l)
How does Fe 2+ convert to Fe 3+ (hint, its very easy and will happen spontaneously over time )
exposure to O2
What colour is Fe2+ when dissolved in water
pale green
What colour is Fe3+ when dissolved in water
yellow/brown
What colour is Fe2+ when dissolved in hydroxide
dark green ppt
What colour is Fe3+ when dissolved in hydroxide
brown ppt
what would you observe as a reaction happens when reducing Fe3+ back to Fe2+
colour change from brown/yellow to pale green
What is a way to remember the colour is vanadium ions and what starts where
You = yellow V5+
Better = blue
Get = green
Vanadium = violet V2+
what colour is V5+
yellow
what colour is V4+
blue
what colour is V3+
green
what colour is V2+
violet
what colour is dichromate 6+
orange
what colour is chromate 6+
yellow
what colour is Cr 3+
green
what colour is Cr 2+
blue
in most reactions with transition metals that we need to know, a precipitate is formed. see below
[M(H2O)6]2+(aq) + 2NH3(aq) –> M(H2O)4(OH)2 + 2NH4+(aq)
why does a precipitate form and not an aqueous solution?
- solution is water, and water is polar
- the species that holds the transition metal changes from a polar substance with a 2+ charge to a neutral substance with no charge, essentially non-polar
- like will dissolve like, so water will NOT dissolve the non polar species as itself is polar
why is dichromate stable in acid
finish the equation
[Co(H2O)6(aq) + 4Cl-(aq) –>
[Co(H2O)6 2+(aq) + 4Cl-(aq) –> [CoCl4)2-(aq) +6H2O
what colour is aqueous Copper
pale blue
what colour is aqueous cobalt
pink
what colour is aqueous chromium
dark green
what is formed when copper is in OH-
blue ppt
what is formed when cobalt is in OH-
blue ppt
what colour is chromium in OH-
dark green ppt
what colour is chromium in excess OH-
dark green solution
what colour is copper in excess NH3
royal blue solution
what colour is cobalt in excess NH3
brown solution
what colour is chromium in excess NH3
violet solution
what colour is copper in Cl-
fluorescent yellow solution
what colour is cobalt in Cl-
blue solution
whats a good way to remember Fe3+ is yellow and brown
3 fingers held up looks like a w, and w is in broWn and yelloW
