Transition Metals

Question 1

What are transition metals?

Answer 1

Elements with an incomplete d-sub shell that can form at least 1 stable ion with an incomplete d-sub shell

Question 2

2 exceptions to the Aufbau principle?

Answer 2

Chromium
Copper
- 1 electron promoted from 4s to the 3d
- more energetically stable in this form

Question 3

Properties of transition metals?

Answer 3

Variable oxidation states
Form complex ions
Form coloured compounds
Behave as catalysts

Question 4

How are variable oxidation numbers achieved in transition metals ? And why?

Answer 4

When transition elements form ions , they lose electrons from the 4s sub shell first
Becuase :
when orbitals occupied, repulsion between electrons pushes the 4s into a higher energy state so slightly higher in energy than 3d subshell
The 4s is the outer shell/loses electrons first

Roman numeral indicate ox. States of the ion

Question 5

What is a ligand?

Answer 5

An atom,ion or molecule that donates a pair of electrons to a central metal atom/ion
- must have at least 1 lone pair to form DATIVE BOND

Question 6

Which metals are not transition metals?

Answer 6

Scandium - Sc - only form 1 ion (Sc3+) which has empty d subshell
Zinc - Zn - only forms 1 ion (Zn2+) which has a full d subshell

Question 7

What is a complex ion?

Answer 7

Metal ion surrounded by datively covalently (coordinately) bonded ligands

Question 8

What are monodentate, bidentate and multidentate ligands?

Answer 8

MONODENTATE: ligand with one lone pair (H2O, NH3,CL-,OH-)
BIDENTATE: ligands with 2 lone pairs (1,2 diaminoethane,ethanedioate ions(C2O4 2-)) - each form 2 dative covalent bonds with metal ion
MULTIDENTATE* : ligands with more the 2 lone pairs ( EDTA4-has 6 lone pairs (hexadentate) - form 6 dative bonds its metal ion)

Question 9

What is coordination number?

Answer 9

Number of coordinate bonds to central atom/ion

Question 10

How to name complexes?

Answer 10

If overall ion is cation (+) then:
Prefix of no. Ligands , ligand name , element, ox number
Prefixes include: Di (2), tetra (4), hexa (6)

If overall ion is anion (-) then:
Name of element ENDS IN -ATE + sometimes Latin word stems are used
E.g (tetrachlorcuprate (II) ) cuprate - copper

Question 11

How to find charge of complex ion?

Answer 11

Sum of ox states of all species present

Question 12

Why are transition metal compounds colored?

Answer 12

Absorb energy corresponding to certain parts of visible electromagnetic spectrum
- colours absorbed are complementary to colour observed

Question 13

What are complementary colours?

Answer 13

Any 2 colours which are directly opposite each other in colour wheel ( if green is observed, red will be absorbed )

Question 14

Why are Zn2+m Sc3+ ions not coloured?

Answer 14

Have completely filled/empty 3d energy levels

Question 15

What happens to 3d subshell when ligand bond to metal ions?

Answer 15

3d orbitals split into 2 different energy levels
If electrons in lower energy level absorb energy from visible light spectrum —> MOVE TO HIGHER ENERGY LEVEL (PROMOTION/EXCITATION)
- to jump move to higher energy level ,they
need energy = energy gap (ΔE)
- larger the energy gap , higher the frequency of light absorbed, lower the wavelengths

Question 16

What does the amount of energy (and frequency of light) needed to move to higher energy level depend on?

Answer 16

Central metal ion/ its nuclear charge
Oxidation number of metal
Ligands (size/type)
Coordination number/shape of complex

THEY ALL AFFECT SIZE OF ENERGY GAP

Question 17

How does size/type of ligand affect ΔE/colour observed?

Answer 17

Ligands have different CHARGE DENSITIES
Greater charge density—> the stronger the ligand interacts with metal ion —> greater splitting of d-orbitals —> more energy needed to promote electrons
- therefore shifted to region of visible light spectrum with HIGHER FREQUENCY/lower wavelengths
- different colour of light absorbed/ complementary colour observed (same metal but different ligands can have different colour)

Question 18

How does oxidation number affect ΔE/colour?

Answer 18

Higher ox number of metal, stronger interaction with ligand —> —> greater splitting of d-orbitals —> greater ΔE —> higher frequency of light absorbed —> different colour observed/absorbed
E.g Fe(II): [Fe(H2O)6]2+ absorbs in the red region and appears green
Fe(III): [Fe(H2O)6]3+ absorbs in blue region and appears orange

Question 19

How does coordination number affect ΔE/colour?

Answer 19

Change in coordination no./geometry of complex ion/change in ligand changes colour as they alter strength of interactions between metal ion/ligand

Splitting energy (ΔE) of d orbitals affected by orientation of ligands/d orbitals

Question 20

Octahedral complex - coordination no.,bond angle?

Answer 20

COORDINATION NO. : 6
BOND ANGLE : 90 degrees

Question 21

Tetrahedral complex: coordination no. And bond angle?

Answer 21

Coordination no. : 4
Bond angle : 109.5 degrees

(Cl- common ligand for this shape which are quite large)

Question 22

Structure of cis platin?

Answer 22

Bond: 4 coordinate bonds - square planar (not tetrahedral)
Complex of platinum (II) with 2 Cl atoms, 2 NH3 molecules (same group on same side)
Bond angle: 90 degrees

Question 23

Why is cis platin used for cancer treatment supplied as a cis isomer instead of its trans form?

Answer 23

Trans platin is toxic (same groups on opposite sides)

Question 24

Structure of haemoglobin?

Answer 24

Contains Multidentate ligand made up of 4 haem groups ,
- iron (II) at its centre
Nitrogen atom from each haem group form dative covalent bond to Fe2+ ion in a square planar complex
5th dative bond from protein (globin) to Fe2+ ion

Question 25

Ligand exchange of haemoglobin example?

Answer 25

Normally,Oxygen atoms form dative bond with iron(II) , but bnd weakly (to break off/be transported into cells) CO is better ligand and bind strongly, irreversibly to iron(II) - prevent O2 binding

Question 26

Why are transition metals used as catalysts?

Answer 26

Can form more than 1 stable ox state so can accept/lose electrons easily means they can catalyse some redox reactions ( can be reduced/oxidised again or vice versa)

Question 27

2 types of catalyst?

Answer 27

**Heterogeneous**: catalyst in different physical state from reactants - reaction occurs at active sites on surface of catalyst E.g using IRON in haber process ( N2 + 3H2–> 2NH3) **homogeneous** : catalyst in same physical state as reactants

Question 28

How does heterogenous catalyst work?

Answer 28

Usually solid/reactnats are gaseous/in solution SURFACE ADSORPTION THEORY 1. ADSORPTION: one or more reactnats attached to surface of catalyst - can lead to catalytic action 2. bonds between reactant molecules weakened or molecules held in a more reactive configuration 3. DESORPTION: reaction product becomes detached from surface of catalyst

Question 29

What happens if a metal has too strong/too weak adsorption to catalyst?

Answer 29

Products cannot be released (metal W)/ cant adsorb in high enough concentration (Ag) (Ni/Pt have the right strength so most useful as catalyst)

Question 30

How is the surface area of heterogenous catalyst maximised?

Answer 30

A support medium is used - minimises cost as well as

Question 31

Advantages of heterogenous catalysts?

Answer 31

- heterogenous catalyts can be filtered off/easy to separate from liquid or gaseous products - good for continuous processes (rather than batch processes)

Question 32

Eg of heterogenous catalyst in contact process? What does this show?

Answer 32

***V2O5 - catalyst in manufacturing sulfuric acid** **overall: 2SO2 + O2 —> 2SO3** Step 1: **SO2 + V2O5 —> SO3 + V2O4** (Ox no. Of vanadium decreases from +5 TO -4) Step 2 : **2V2O4 + O2 —> 2V2O5** (Vanadium(V) oxide regenerated by reacting with oxygen) V goes from +4 to +5 - shows that variable oxidation state can be utilised in heterogenous catalysis

Question 33

What does catalytic converters do ?

Answer 33

Remove CO, NO and unburned hydrocarbons from exhaust gases , Turing them into less harmful CO2 , N2, H2O 2No + 2CO —> N2 + 2CO2 CH3CH2CH3 + 5O2 —> 3CO2 + 4H2O

Question 34

Method of action of catalytic converters?

Answer 34

Uses SURFACE ADSORPTION THEORY 1. **CO and NO form bonds with active sites** on surface of catalyst - adsorbed 2. Results in bonds in reactants to **weaken/break** 3. **New bonds form** between the reactants held close tgt on catalyst surface 4. **Desorption** of CO2 AND N2 product molecules

Question 35

How to minimise cost and efficiency of catalyst ?

Answer 35

- Increase SA of catalyst Achieved by coating inert surface medium with catalyst (platinum, palladium,rhodium) - reduce amounts of catalyst used Done by spreading catalyst over honeycomb support medium

Question 36

What happens in homogeneous catalysis ? What does this reaction show?

Answer 36

- all reactants in same phase (all in gaseous/in solution) Homogenous catalyst react with reactants to form an **intermediate species**, which then reacts to form products and reform the catalyst Ea needed to form intermediates and form the products from intermediates is LOWER than Ea needed to form prodcuts straight from reactants - intermediate has different ox state to original transition metal catalyst/ at the end of reaction , original ox state will reoccur SHOWS IMPORTANCE OF VARIABLE OX STATES of transition metals in catalysis

Question 37

Why can transition element ions act as homogenous catalysts?

Answer 37

Have more than 1 stable ox state - so they can accept/lose electrons easily to go from 1 ox state to another ( so catalyse redox reactions by acting as reducing/oxidising agents) Iron often used as can form Fe(II) and Fe(III)

Question 38

E.g of homogeneous catalyst?

Answer 38

Reaction between iodide and persulfate ions Overall : S2O8 2- + 2I- —> 2SO4 2- + I2 (catalysed by Fe2+ - slow bc **repulsion of 2 negative ions so high Ea)** Fe3+ + e- —> Fe2+ (Fe(II) acts as **reducing agent/gets oxidised itself**) If iron (II) added , rate is quicker - LOWERS Ea S2O82- + 2Fe2+ → 2SO42- + 2Fe3+ (Fe3+ is the intermediate species) -peroxodisulfate **reduced** to sulfate ions /iron (III) produced** 2I- + 2Fe3+ → I2 + 2Fe2+ **Iron (III) oxidise iodide ions / reduced themselves to Fe(II)** Both stages involve collisions between + and - ions so lower Ea

Question 39

How does homogeneous catalysts work in terms of electrode potentials?

Answer 39

Homogeneous catalyst’s electrode potential must **lie between electrode potentials of the 2 reactants** - so can **reduce reactant** with more + electrode potential - and **oxidise reactant** with more negative electrode potential

Question 40

What does the E value show us in homogeneous catalysis?

Answer 40

Shows if catalysis is possible - doesn’t guarantee rate of reaction will be increased

Question 41

Autocatalysis example? Reaction between ethanedioate and manganate ions?

Answer 41

Overall: **2MnO4- + 5C2O4 2- + 16H+ —> 2Mn2+ + 10CO2 + 8H2O** Reaction is slow as it is a collision between 2 **negative ions - repel** - INCREASED Ea Mn2+ ion product is AUTOCATALYST + speeds up reaction as brings **alternative route with lower Ea** **Catalysed route:** Step 1 : 4Mn2+ + MnO4– + 8H+ → 5Mn3+ + 4H2O 2Mn3+ + C2O42- → 2CO2 + 2Mn2+ **Mn2+ regenerated here** **Reaction starts to slow as MnO4 - conc drops**

Question 42

How is the rate of reaction between ethanedioate and manganate ions measured? Advantages of this method?

Answer 42

Remove samples at set times+ **titrate** to work out conc of MnO4- **Colorimeter** - rate at which **purple Mn(VII) consumed** accelerates with time - doesn’t disrupt reaction mixture - quicker determination of conc

Question 43

How do impurities reduce efficiency of heterogenous catalyst?

Answer 43

The impurities can: **Adsorb onto catalyst surface** and occupy active sites **Prevent bond weakening** in the reactants 'Take up' the surface area of catalyst by **forming strong bonds to surface of catalyst** so are **less likely to desorb** from surface of catalyst