15 - Transition Metals [SET 2] Flashcards
What makes an element a transition metal?
When it has partially filled d-orbitals in one or more of its ions.
What makes an element a d block element?
When its last electron has gone into a d-orbital
What is the difference between a d-block element and a transition metal?
Some d-block elements have ions that do not partially fill the d orbitals making it not a transition metal.
What gives transition metals its characteristics?
Its partially filled d orbitals
What are the characteristics of transition metals?
- Complex formation
- Forms coloured ions
- Variable oxidation states
- Catalytic activity
Why is Zinc not a transition metal?
Zinc can only form Zn 2+ ion. This ion has a COMPLETE d orbital. Whereas transition metals have an incomplete d orbital.
Why is Scandium not a transition metal?
Scandium can only form Sc 3+ ion. This ion has an EMPTY d orbital. Whereas transition metals have an incomplete d orbital.
What is the successive ionization energy for the elements Sc to Zn?
A gradual increase in ionisation
energy until all the 4s and 3d electrons have been removed. Then there is a big jump as electrons start to be removed from the inner shells
What is a complex ion?
A complex ion is a central metal ion surrounded by ligands.
What is a ligand?
A ligand is an atom, ion or molecule which can donate a lone electron pair
What bonding is involved in complex formation?
Dative bonding
What is a dative bond?
A dative bond is when the shared pair of electrons in the covalent bond comes from only one of the bonding atoms.
What is a co-ordination number?
The number of dative bonds formed to a central metal ion.
What is a monodentate ligand?
A ligand that can form only one dative bond per ligand.
What is a multidentate ligand?
A ligand that can form multiple dative bonds per ligand with the lone pair from multiple different atoms in the same molecule.
What is a bidentate ligand?
A ligand that can form two dative bonds per ligand with the lone pair from two different atoms in the same molecule.
What is the co-ordination number or the ion when it reacts with EDTA and what is the charge of an EDTA ion?
co-ordination number of 6
charge of -4
What causes colour changes and why?
- Oxidation state
- Change of co-ordination number
- Change of ligand
- This will alter the energy required to excite electrons/the energy split between the d orbitals. Hence change of frequency of light.
What causes the colour of ions?
When the electrons in the d orbital get excited and jump from a lower energy level to a higher energy level (different d orbitals). A part of visible light is absorbed and the complementary colour is shown.
Why does the scandium ion have no colour?
Its ion, Sc 3+, has no electrons in the d orbitals. So there are no electrons that could be promoted to a higher energy level. So there is no energy transfer equal to
that of visible light.
What ions are colourless?
Sc 3+
Zn 2+
Cu +
Why are Zn 2+ and Cu + ions colourless?
The d orbitals are full and there is no space for electrons to be transferred to a higher energy state.
What is the shape of a complex ion with 6 dative bonds?
octahedral
What is the shape of a complex ion with 4 dative bonds?
tetrahedral (more common)
square planar
What is the shape of a complex ion with 2 dative bonds?
linear
Ag + commonly forms these
What is cisplatin used for?
It is used as an anticancer drug
Why does only cisplatin work and not transplatin?
The cisplatin version only works as two chloride ions are displaced and
the molecule joins onto the DNA. In doing this it stops the replication of
cancerous cells as it distorts the shape of the DNA.
How does a cisplatin molecule bond with DNA?
- One chloride ligand is substituted with water.
- The same water ligand is then substituted with one of the guanine nitrogen atoms.
- A dative (covalent) bond formed between the lone pair on the nitrogen on the guanine base and the central platinum ion at the centre.
- Repeat for the other chloride ligand.
- The DNA shape is distorted.
What is the disadvantage of cisplatin?
It can not differentiate between healthy and cancerous cells. It can bind onto healthy DNA and lead to side effects like hair loss.
What allows haemoglobin to transport oxygen in the blood?
The Fe (II).
What is haem?
An iron (II) complex with a multidentate ligand.
Why is CO toxic to humans?
CO can form STRONG dative bonds with haemoglobin and replaces oxygen in the ligand exchange reaction and prevent other oxygens from attaching to the haemoglobin.
What electrons are lost when transition metals are forming ions?
The 4s electrons are lost before 3d.
Why can transition metals have various oxidation states?
They can donate and receive electrons and can oxidize and reduce. This is because the ions contain partially filled sub-shells of d electrons that can easily lose or gain electrons. The energy differences between the oxidation states are small.
What compounds tend to be oxidising agents (be reduced in reaction)?
Compounds with high oxidation states tend to be oxidising agents e.g MnO4 - (VII)
What compounds tend to be reducing agents (be oxidised in reaction)?
Compounds with low oxidation states are often reducing agents e.g V 2+ (II) & Fe 2+ (II)
What are the main oxidation states, ions and colours of vanadium?
+5, VO2 + (dioxovanadium), VO3 + (vanadate), yellow
+4, VO 2+, blue
+3, V 3+, green
+2,V 2+, violet
What is the mnemonic for the colours of vanadium ions?
Yogi Bear Gets Violent
e l r i
l u e o
l e e l
o n e
w t
What happens when you add zinc to vanadium (V) in acidic solution?
It will reduce the vanadium through each successive oxidation state. Colour changes from yellow to (green) to blue to green to violet.
Why does zinc reduce vanadium (V) to (II)?
Zinc has a more negative electrode potential than all the vanadium half equations.
What are the main oxidation states, ions and colours of chromium?
+6, Cr2O7 2-, Orange
+3, Cr 3+, Green
+2, Cr 2+, Blue
Why is a bung/lid/hydrogen atmosphere needed when reacting zinc and dichromate together?
The oxygen in the air can oxidise Cr 2+ up to Cr 3+.
How do you make transition metals in acidic solution more easily oxidised?
Add excess NaOH so its in alkaline conditions
Describe the formation of complex ions in terms of Bronstead-Lewis acid and base
The ligand is the B-L base because it is donating a pair of electrons in the dative covalent bond and the metal ion is the B-L acid.
What is formed when metal ions are in an aqueous solution?
Metal aqua ions
Why might an aqueous solution of metal ions be acidic?
The following equilibria happen in aqueous solutions of metal ions
[M(H2O)6] 2+ + H2O <—-> [M(H2O)5(OH)] + + H3O +
[M(H2O)6] 3+ + H2O <—-> [M(H2O)5(OH)] 2+ + H3O +
H3O + is acidic
Why would a 3+ metal aqua ion be more acidic than a 2+ metal aqua ion?
The 3+ metal ions have higher charge density and have greater polarising power. The greater the polarising power, the more
strongly it attracts the water molecule. This weakens the O-H bond so it breaks more easily releasing H+ ions.
What reaction occurs when SOME OH- or NH3 is added to a metal aqua ion?
Deprotonation acid-base reactions.
Ligand exchange with OH-
Precipitates formed
Give the equation when some NaOH is added to a solution of +2 metal aqua ions. Include state symbols
[M(H2O)6] 2+ (aq) + 2 OH - (aq) —> [M(OH)2(H2O)4] (s) + 2 H2O (l)
Give the equation when some NH3 is added to a solution of +2 metal aqua ions. Include state symbols
[M(H2O)6] 2+ (aq) + 2 OH - (aq) —> [M(OH)2(H2O)4] (s) + 2 H2O (l)
Give the equation when some NaOH is added to a solution of +3 metal aqua ions. Include state symbols
[M(H2O)6] 3+ (aq) + 3 OH - (aq) —> [M(OH)3(H2O)3] (s) + 3 H2O (l)
Give the equation when some NH3 is added to a solution of +3 metal aqua ions. Include state symbols
[M(H2O)6] 3+ (aq) + 3 OH - (aq) —> [M(OH)3(H2O)3] (s) + 3 H2O (l)
What do OH- and NH3 ions act as in deprotonation reactions?
B-L bases as they are accepting protons
What is amphoteric behaviour?
Reacting and dissolving in both acid and bases
Give the equation of trihydroxotriaquachromium (III) in acid solution. Include state symbols.
[Cr(H2O)3(OH)3] (s) + 3 H+ (aq ) [Cr(H2O)6] 3+(aq)
When reacting with excess NH3, what does the NH3 act as?
B-L base
What do you need to do ligand exchange with Cl -?
By adding a high concentration of chloride ions (from conc HCl or saturated NaCl) to aqueous ions.
What happens to the co-ordination number when doing ligand exchange?
If the ligands are the same size, the co-ordination number will stay the same. E.g. H2O and NH3
If the ligands are not the same size, there will be a change. E.g. H2O and Cl-
What is the difference in stability between complex ions with mono/bi/multidentate ligands?
Complex ions with multidentate ligands is more stable than bidentate ligands which is also more stable than monodentate ligands.
Why is an ion with multidentate ligands more stable than an ion with mono/bidentate ion?
When an ion with mono/bidentate ligands reacts with a solution with multidentate ligands,
-Increase in entropy, due to the increase of moles from LHS to RHS.
-Enthalpy change (and ΔS surroundings) is near zero, due no. of dative bonds and type are the same.
-Energy required to break bonds is the same.
-Therefore ΔS Total will be positive and the complex formed is stable.
Why molecules like NH2NH2 cannot act like a bidentate ligand?
They are too small and the lone pairs are too close to each other and would not be able to fit around the ion.
How to work out the formulae of a chloride-containing complex?
Use silver nitrate to separate the chlorides bonding ionically.
e.g. Co(NH3)6Cl3
If 3 moles of AgNO3 react with one mole of this, there is 3 Cl- outside the complex bonding ionically not dative covalent like a ligand.
Same for 2 and 1 moles.
What is a heterogenous catalyst?
A catalyst in a different phase from the reactants
What is a homogenous catalyst?
A catalyst in the same phase from the reactants
What phase are the catalyst and the reactants in when a heterogenous catalyst is used?
The catalyst is typically a solid.
The reactants are gaseous or liquid.
What is adsorption?
When the reactants attach to the surface of the catalyst
