Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Chemistry A- Level > Transition Metals > Flashcards

Transition Metals Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Chemistry flashcards Periodic Table flashcards Chemistry 101 flashcards Organic Chemistry 101 flashcards
1
Q

What are transition metals?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

2 exceptions to the Aufbau principle?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Properties of transition metals?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

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

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is a ligand?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Which metals are not transition metals?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is a complex ion?

A

Metal ion rounded by datively covalently (coordinately) bonded ligands

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are monodentate, bidentate and multidentate ligands?

A

MONODENTATE: ligand with one lone pair (H2O, NH3,CL-,OH-)
BIDENTATE: ligands with 2 lone pairs (1,2 diaminoethane) - 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)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is coordination number?

A

Number of coordinate bonds to central atom/ion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How to name complexes?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How to find charge of complex ion?

A

Sum of ox states of all species present

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Why are transition metal compounds colored?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are complementary colours?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Why are Zn2+m Sc3+ ions not coloured?

A

Have completely filled/empty 3d energy levels

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

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

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

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

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

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

A

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)

18
Q

How does oxidation number affect ΔE/colour?

A

Higher ox number of metal, stronger interaction with ligand —> 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

19
Q

How does coordination number affect ΔE/colour?

A

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

20
Q

Octahedral complex - coordination no.,bond angle?

A

COORDINATION NO. : 6
BOND ANGLE : 90 degrees

21
Q

Tetrahedral complex: coordination no. And bond angle?

A

Coordination no. : 4
Bond angle : 109.5 degrees

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

22
Q

Structure of cis platin?

A

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

23
Q

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

A

Trans platin is toxic (same groups on opposite sides)

24
Q

Structure of haemoglobin?

A

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

25
Q

Ligand exchange of haemoglobin example?

A

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

26
Q

Why are transition metals used as catalysts?

A

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)

27
Q

2 types of catalyst?

A

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

28
Q

How does heterogenous catalyst work?

A

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

29
Q

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

A

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

30
Q

How is the surface area of heterogenous catalyst maximised?

A

A support medium is used
- minimises cost as well as

31
Q

Advantages of heterogenous catalysts?

A
  • heterogenous catalyts can be filtered off/easy to separate from liquid or gaseous products
  • good for continuous processes (rather than batch processes)
32
Q

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

A

*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
33
Q

What does catalytic converters do ?

A

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

34
Q

Method of action of catalytic converters?

A

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

35
Q

How to minimise cost and efficiency of catalyst ?

A
  • Increase SA of catalyst
  • Coat inert surface medium with catalyst (platinum, palladium,rhodium) - reduce amounts of catalyst used
    Done by spreading catalyst over honeycomb like structure
36
Q

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

A
  • all reactants in same phase (all in gaseous/in solution)
    Formation of intermediate species
  • intermediate has different ox state to original transition metal/ at the end of reaction , original ox state will reoccur
    SHOWS IMPORTANCE OF VARIABLE OX STATES of transition metals in catalysis
37
Q

Why can transition element ions act as homogenous catalysts?

A

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)

38
Q

E.g of homogeneous catalyst?

A

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+
-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

39
Q

How does homogeneous catalysts work in terms of electrode potentials?

A

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

40
Q

What does the E value show us in homogeneous catalysis?

A

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

41
Q

Autocatalysis example? Reaction between ethanedioate and manganate ions?

A

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

42
Q

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

A

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

Chemistry A- Level (23 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions