AC20: Transition Metals Flashcards
Define a transition metal
Transition metals are d-block elements that can form at least one stable ion with a partially complete d-subshell
What two d-block elements are not Transition metals
Scandium and Zinc
Why is Scandium not a transition metal
can only form Sc 3+ ion which has an empty d-subshell
Why is Zinc not a transition metal
can only form Zn 2+ ion which has a fully filled d-subshell
What colour are scandium and zinc compound and how is this significant
they are white, compared with other d-block compounds that are often coloured
What are the 2 transition metal atoms that do not follow the electron configuration for all other transition metal atoms and how can you remember them
Chromium (Cr) and copper (Cu)
Crafty and Cunning
How does Chromium not follow the rules for electron configuration of T.M. atoms
chromium - 4s1 3d5
it has a half-filled 3d-subshell rather than a full 4s subshell as this is more stable than 4s2 3d4
How does Copper not follow the rules for electron configuration of T.M. atoms
copper - 4s1 3d10
it has a fully-filled 3d-subshell rather than a full 4s subshell as hit is more stable than 4s2 3d9
What is different in the electron configuration of T.M. ions compared to other ions
remove electrons from 4s subshell before 3d subshell
State the properties of all metals
shiny when freshly cut
relatively high densities
high melting/boiling points - due to giant metallic lattice structure
good conductors of heat and electricity - due to mobile electrons
State 3 properties that only transition metals have (that other metals may not)
1- can form coloured compounds
2- some T.M.s and T.M. compounds can act as catalysts
3- ability to form variable oxidation states
Explain how T.M.s can form coloured compounds and give an example with Fe
Due to partially filled d-subshells, these can be different for a particular T.M. depending on its O.N.
e.g. Fe 2+ (aqueous) = pale green
Fe 3+ (aqueous) = yellow
Explain how some T.M.s and T.M. compounds can act as catalysts and give an example with nickel/platinum acting as a catalyst in the hydrogenation of alkenes
Variable O.N.s allow T.M.s to act as catalysts as they can : -donate/accept electrons to/from reactants
-allow reactants to adsorb to its surface and weaken the reactants’ bonds in the process
e.g. alkaline adsorption between nickel and C=C pi-electron which weakens the pi-bond
H2 adsorbs to nickel and weakens bond
List all the variable oxidation states for T.M.s
Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn
+1
+2, +2, +2, +2, +2, +2, +2, +2, +2
+3,+3, +3, +3, +3, +3, +3, +3, +3
+4, +4, +4, +4, +4, +4, +4
+5, +5, +5, +5, +5
+6, +6, +6
+7
How can oxidation numbers of >+3 in transition metals exist and give an example for Mn, and for Cr
cannot exist in monatomic ions but can exist in polyatomic ions where the metal is bonded to oxygen
e.g. MnO4 -, Cr2O7 2-
Explain what a complex ion is
A complex ion consists of a central metal ion datively bonded to a number of ligands, which donate electron pairs to form dative covalent (coordinate) bond(s)
Explain what a ligand is
A ligand is an ion or molecule with at least one lone pair of electrons that donates to a central metal ion, forming coordinate bond(s)
What property of transition metal ions allow them to form coordinate bonds with ligands
high charge density and therefore strong electrostatic attraction
How do you work out the coordination number of a complex ion
number of coordinate bonds = coordination number
What are the bond angles in an octahedral complex ion
90 and 180
What is a monodentate/unidentate ligand and give an example
a ligand that can form only ONE coordinate bond to a central metal ion
e.g. H2O, Cl-, NH3
What are bidentate ligands and give the 2 common examples for OCR
ligands that can form 2 coordinate bonds to a central metal ion.
e.g. 1,2-diaminoethane (“en”)
ethandioate ion
What are multidentate ligands and give an example found in our bodies
ligands that can form more than 2 coordinate bonds around a central metal ion
e.g. haemoglobin - tetradentate (4)
When does ligand substitution occur
1- a ligand capable of forming stronger coordinate bonds is added
2- a high concentration of a ligand is added to displace another, since ligand substitution is a reversible process, it will follow Le Châtelier’s principle
Give the equation for the reaction between aqueous copper (2) and concentrated HCl, giving the colours for each reaction stage
[Cu(H2O)₆]²⁺(aq) + 4Cl⁻ (aq) <-> [CuCl₄]²⁻ (aq) + 6H₂O (l)
where [Cu(H2O)₆]²⁺(aq) is blue
[CuCl₄]²⁻ (aq) is yellow
and at equilibrium is green
Give the equation for the reaction between aqueous copper (2) and excess aqueous ammonia, giving the colours for each reaction stage
[Cu(H2O)₆]²⁺(aq) + 4NH₃(aq) <-> [Cu(H2O)₂(NH₃)₄]²⁺ (aq) + 4H₂O (l)
where [Cu(H2O)₆]²⁺(aq) is blue
[Cu(H2O)₂(NH₃)₄]²⁺ (aq) is deep blue
Give the equation for the reaction between aqueous chromium (3) and excess aqueous ammonia, giving the colours for each reaction stage
[Cr(H2O)₆]³⁺(aq) + 6NH₃(aq) <-> [Cr(NH₃)₆]³⁺ (aq) + 6H₂O (l)
where [Cr(H2O)₆]³⁺(aq) is violet
[Cr(NH₃)₆]³⁺ (aq) is purple
what property of CO makes CO so dangerous to humans and what are you given if you have CO poisoning
The binding affinity of CO is around 200x greater than O2 and so CO can reduce the ability of Hb to bind with O2 significantly. Patients with CO poisoning are given high [O2] to breathe to shift the equilibrium and dispalce CO via ligand substitution
What are the 2 types of stereoisomerism that complex ions carry out
1- cis-trans
2- optical
What shapes of complex ions does cis-trans isomerism only occur in
octahedral and square planar complex ions, not in tetrahedral
What is the key difference in function of cis-platin and trans-platin
cis-platin is a cancer treatment which binds to DNA to prevent cel division
trans-platin does not prevent cell division
In octahedral complex ions, what is the difference in bond angles for cis and trans isomers, use [Co(Cl)₂(NH₃)₄]⁺ as an example
in cis-isomer of [Co(Cl)₂(NH₃)₄]⁺, Cl- ligands are at 90º apart
in trans isomer of [Co(Cl)₂(NH₃)₄]⁺, Cl- ligands are at 180º apart
In octahedral complex ions, what is the difference in bond angles for cis and trans isomers, use [Cr(Cl)₃(NH₃)₃]⁰ as an example
in cis-isomer of [Cr(Cl)₃(NH₃)₃]⁰, Cl- ligands are all at 90º apart
in trans isomer of [Cr(Cl)₃(NH₃)₃]⁰, at least one pair of Cl- are at 180º apart
What shapes of complex ions does optical isomerism only occur in
octahedral complex ions with 2 or more bidentate ligands
What is the colour of Cu²⁺(aq) ( or [Cu(H2O)₆]²⁺(aq) )
blue
What is the colour of Fe²⁺(aq) ( or [Fe(H2O)₆]²⁺(aq) )
pale green
What is the colour of Fe³⁺(aq) ( or [Fe(H2O)₆]³⁺(aq) )
pale yellow
What is the colour of Cr³⁺(aq) ( or [Cr(H2O)₆]³⁺(aq) ), and what colour is it often due to the presence of common anions
violet
or often green
What is the colour of Mn²⁺(aq) ( or [Mn(H2O)₆]²⁺(aq) )
pale pink
What are the 2 types of precipitation reactions that occur with T.M. hexaaqua ions, what charges of T.M. hexaaqua ions do they only occur with, and what is formed
with NaOH (aq) and NH3(aq)
only with T.M. hexaaqua ions of 2+ or 3+ charges
forms insoluble metal hydroxides
What is the colour of Cu(OH)₂ (s)
blue ppt
What is the colour of Fe(OH)₂ (s)
green ppt
What is the colour of Fe(OH)₃ (s)
orange/brown ppt
What is the colour of Cr(OH)₃ (s)
grey-green ppt
What is the colour of Mn(OH)₂ (s)
light brown ppt
What happens when excess OH-(aq) is added to T.M. hydroxide ppts
Cr(OH)₃ (s) redissolves to form Cr(OH)₃ (aq) which is a dark green solution
Mn(OH)₂ (s), Fe(OH)₃ (s), Fe(OH)₂ (s), Cu(OH)₂ (s) are insoluble in excess OH- (aq)
What are the 2 stages of hexaaqua ions reacting with aqueous ammonia
1- ammonia in water reacts to form OH- ions
NH3 + H2O <-> NH4+ + OH-
The hydroxide ions react with hexaaqua T.M. ions to form T.M. hydroxide ppts
2- in excess ammonia, only Cu(OH)₂ (s) and Cr(OH)₃ (s) redissolve
What are the two hexaaqua transition metal ions that redissolve in excess ammonia and how do you remember them
only Cu(OH)₂ (s) and Cr(OH)₃ (s)
Cunning and Crafty
What is the colour of [Cu(H2O)₂(NH₃)₄]²⁺ (aq)
[Cu(H2O)₂(NH₃)₄]²⁺ (aq) is deep blue solution
What is the colour of [Cr(NH₃)₆]³⁺ (aq)
[Cr(NH₃)₆]³⁺ (aq) is purple solution
What is the colour of the solution formed when Fe²⁺ is oxidised to Fe³⁺ by MnO4-
very pale pink/solution
What is the colour of the solution formed when Fe³⁺ is reduced to Fe²⁺ by I-
(pale green + brown)
dirty green
What is the colour of the solution formed when Cr2O7 2- is reduced to Cr³⁺ by Zn(s)
green (due to presence of other anions, colour is green not violet)
What is the colour of CuI (s)
white solid
What is the colour of Cu₂O (s)
red solid
What is a coordinate bond
a covalent bond where both electrons in the shared pair come from the same atom
Explain why carbon monoxide is highly toxic
CO can replace O2 as a ligand. CO forms a stronger coordinate bond than O2 and so will bind preferentially, so the Hb loses its ability to transport O2
What is the shape of platinum complexes
square planar
Explain the term ‘coordination number’
number of coordinate bonds formed by the ligands to the metal ion in a complex
