Brainscape's Knowledge GenomeTM

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


See full index

La Chimie H2 > Transition Elements > Flashcards

Transition Elements Flashcards

1
Q

Define transition element

A

a d-block element that form at least 1 stable ion w PARTIALLY-filled d subshell

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

Name exceptions electronic configuration of transition elements

A
  • Cr & Cu, hv lone 4s e-
    bcos,
  • extra stability fr symmetrical distribut n of charge ard nucleus for half-filled/fully filled 3d subshell for Cr & Cu
    e- config of Cr: [Ar]3d5 4s1, NOT 3d4 4s2
    e- config of Cu is [Ar]3d10 4s1, NOT 3d9 4s2
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Why is Sc and Zn not classified as transition elements?

A
  • all ions formed by Sc (Sc3+, *Sc2+ is unstable) & Zn (Zn2+) hv no partially-filled d subshell

electric config:

Sc: [Ar]3d1 4s2
Sc3+: [Ar] (no d e-)

Zn: [Ar]3d10 4s2
Zn2+: [Ar]3d10 (completely filled d subshell)

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

Describe chemical and physical properties of transition elements

A

transit n elements r:
- harder, hv higher densities
- hv higher mp, bp
- form cpd which show transit n elements’ variety of OS
- form cpd that show catalytic activity
- form coloured cpd, ion
- show great tendency form stable complexes

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

Describe how atomic and ionic radius of transition elements change across series

A
  • across T.E. series, atomic/ionic radii relatively invariant (unchanged)
    bcos,
    across series,
  • nuclear charge increase
  • e- added to inner 3d orbital, provide shielding for 4s e-
  • increase in nuclear charge offset by increase shield effect
  • eff nuclear charge vary oni slightly
  • atomic/ionic radius remain relatively invariant

vs
across period 2, 3
- e- added to same outermost quantum shell
- nuclear charge increase but shield effect relatively const
- eff nuclear charge increase
- atomic/ionic radius decrease significantly

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

Describe how ionisation energy of transition element series change in general

A

across T.E. series,

i. 1st & 2nd IE relatively invariant
bcos
- both IE involve remove 4s valence e-
- inner 3d e- provide shielding for outer 4s e-
- increase in nuclear charge offset by increase shield effect
- eff nuclear charge oni slightly vary
- 1st, 2nd IE relatively invariant

ii. 3rd, 4th IE increase significantly
bcos
- involve remove valence e- fr inner 3d subshell
- across series, nuclear charge increase but shield effect remain approx const
- eff nuclear charge increase significantly
- significant increase in 3rd, 4th IE

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

Describe anomalies for ionisation energy of transition element series

A

3rd IE Fe lower than expected, 4th IE for Co lower than expected
*look at e- config, u see paired e-
bcos
- inter-electron repuls n present btw paired d e- in doubly-filled d orbital, so less energy needed remove valence e-

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

Explain why transition elements have a smaller atomic radii and a higher first ionisation energy than s block elements such as Ca

A
  • transit n element hv more proton, so higher nuclear charge than Ca
  • oni slight increase in shield effect as e- added to inner 3d orbital which provide shield for 4s e-
  • there is greater eff nuclear charge, hence stronger e-static attract n btw nucleus & valence 4s e-
    => valence 4s e- more strongly attracted to nucleus
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Explain hardness and density of transition elements

A
  • transit n element harder, denser than s block element
    bcos transit n element:
  • hv relatively smaller atomic radius, thus closer-packed structure
  • hv higher relative atomic mass
    => thus, d-block element hv higher mass per unit volume, so higher density
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Explain melting and boiling points of transition elements

A
  • transit n element hv higher mp, bp than s block element
    bcos
  • tho can both hv giant metallic (lattice) structure
  • in transit n metal, both 3d, 4s e- involved in delocalisat n, so stronger e-static attract n btw cation & sea of delocalised e- (so stronger metallic bond)
  • larger amt energy needed overcome stronger metallic bond to melt
  • thus, higher mp,bp than s block metal

NOTE: in s block metals, oni s e- involved in delocalisat n in metallic bonding, so weaker metallic bond

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

Explain electrical and thermal conductivity of transition elements

A
  • transit n element r better thermal, electrical conductor than s block element
    bcos
  • both 3d, 4s e- available for delocalisat n
  • higher no. of mobile e- act as charge carriers and to conduct heat
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Explain why transition elements (Ti to Cu) have variable oxidation states

A

bcos
- 3d, 4s orbitals close in energies, so variable no. of 4s, 3d e- available for use in bond form n to form ion of similar stability
eg (some common OS)
Ti: +2,3,4
V: +2,3,4,5
Cr: +2,3,6
Mn: +2,4,6,7
Fe: +2,3
Co: +2,3
Ni:+2
Cu: +1,2

  • BUT, s block element hv fixed OS
    bcos,
    once s e- removed, removal of p e- require too much energy, so unfavourable
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Explain standard electrode potentials of transition elements

A

general trend
- -ve Eθ value for Ti, V, Cr show M3+ + e- –> M2+ is less feasible (eqm pos n tends twd oxidat n); hence M3+ more stable wrt M2+, so M2+ easily oxidised, making it good RA
eg Cr2+ oxidised by air to Cr3+
- +ve Eθ value for Mn to Cu show reduct n more feasible (eqm pos n tend twd reduct n); hence M2+ more stable wrt M3+, M3+ easily reduced, so it is good OA
eg Co3+ will b reduced by Cl- form Co2+

anomaly
- Eθ Fe3+/Fe2+ is less +ve than Eθ Mn3+/Mn2+
bcos
- easier to remove e- fr Fe2+ due to inter-electron repuls n btw paired d e- in doubly filled d-orbital (look at electron config)
- so, oxidat n more likely occur for Fe2+, so less +ve Eθ than expected

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

Define transition metal complex

A

complex containing central metal atom/ion attached to ligands thru dative bond
eg [Cu(H2O)6]2+

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

Define ligand

A

molecule or anion containing at least 1 lp e- available to form dative bond w central metal atom/ion

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

Define coordination number

A

no. of dative bonds each central metal atom/ion can form w its ligands

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

Explain why transition element ions can form complex ions

A
  • transit n metal ion hv high charge density, can attract ligands containing at least 1 lp e-
    => high polarising pwr of transit n metal ion produce strong tendency twd covalent bond form n w ligand
  • transit n metal ion hv energetically accessible, vacant d orbitals to accommodate lp e- fr ligands via dative bond
18
Q

Define monodentate ligand, bidentate ligand and polydentate ligand

A
  • monodentate: form oni 1 dative bond per ligand
    eg H2O, NH3
  • bidentate: form 2 dative bond per ligand
    eg ethane-1,2-diamine, ethanedioate
  • polydentate: form > 2 dative bond per ligand
    eg EDTA 4- (hexadentate ligand)
19
Q

Describe shapes of transition element complexes

A

i. coord no. 2
- linear
eg [Ag(NH3)2]+

ii. coord no. 4
- tetrahedral
eg [Cu(CN)4]2-
- square planar
eg [Ni(CN)4]2-

iii. coord no. 6
- octahedral
eg [Cu(EDTA)]2-

20
Q

What to take note about drawing transition element complexes?

A
  • identify correct donor atom (those w appropriate lp e-) of ligand
  • show dative bond fr ligand to central atom/ion
  • draw plane to represent 3D shapes if applicable
    eg for octahedral, tetrahedral, square planar shapes
  • draw square bracket & charge for cationic/anionic complex
21
Q

Explain, in terms of d orbital splitting, why transition element complexes are usually coloured

A
  • a transit n metal ion hv partial fill d orbital; in presence of ligand, d orbital r split into 2 grp w energy gap. This effect aka d orbital splitting
  • during d-d transit n, d e- fr lower energy d orbital absorb certain wavelength light fr visible spectrum, get promoted to higher energy d orbital
  • colour observed is complementary to colour absorbed
22
Q

Explain why d orbitals in an octahedral transition element complex split into two different energy levels

A
  • in octahedral complex, central metal atom surrounded by 6 lp e- (on 6 ligand), along x,y,z axes
  • all 5 d orbital experience e-static repuls n (of mag depending on orientat n of d orbital involved)
  • fr shape, orientat n of d orbital, dx²-y² & dz² orbitals hv their lobe point at ligand along x,y,z axes respectively, so they experience greater repuls n fr ligand
  • BUT, dxy, dxz, dyz orbital experience less repuls n as their lobe r in btw coordinate axes
    => 5 d orbitals r split into 2 energy lvl, w dx²-y² & dz² orbitals hv higher energy lvl, while dxy, dxz, dyz orbital hv lower energy lvl

NOTE:
for other geometries, d orbital r split diff
eg tetrahedral complex, dxy, dxz, dyz orbitals are at higher energy lvl than dx²-y² & dz² orbitals

23
Q

Roughly explain colour wheel for transition element complex

A

NOTE: if sample absorb orange light (eg Cu2+), it appear blue or vice versa (complementary colour, based on colour wheel)

rough complementary colour pairs (+ wavelength)

  • red (640-700nm) & green (450-560nm)
  • orange (600-640nm) & blue (450 - 480nm)
  • yellow (560nm - 600nm) & violet (400-450nm)
24
Q

What affects colour of transition element complexes

A
  • colour depend on energy gap E
    related by E ∝ 1/λ (using photon energy formula)
  • E is affected by following factors:
    1. e- config of metal atom/ion (associated w OS of metal)
    eg
    Fe2+: [Ar]3d6 vs Fe3+: [Ar]3d5 => Fe2+ is blue, Fe3+ is yellow
  1. Ligand field strength (associated w nature of ligand)
    - diff ligand split energy lvl of d orbital to diff extent (amt energy E absorbed by d e- in d-d transit n differ)
    - weak field ligand cause small E, long λ absorbed
    - strong field ligand cause large E, short λ absorbed

*Ligand field strength not to confuse w ligand strength
-> ligand strength refer to ease of replace ligand in complex

25
Q

Give formulae, colour and oxidation state of common transition complexes of V

A
  • [V(H2O)6]2+, violet, +2
  • [V(H2O)6]3+, green, +3
  • [VO(H2O)5]2+, blue, +4
  • [VO2(H2O)4]+, yellow +5
26
Q

Give formulae, colour and oxidation state of common transition complexes/solutions/compounds of Cr

A
  • [Cr(H2O)6]2+, blue, +2
  • [Cr(H2O)6]3+, green, +3
  • [Cr(OH)6]3-, deep/dark green, +3
  • [Cr(NH3)6]3+, purple, +3
  • CrO4 2-, yellow, +6
  • Cr2O7 2-, orange, +6
27
Q

Give formulae, colour and oxidation state of common transition complexes/solutions/compounds of Mn

A
  • [Mn(H2O)6]2+, pale pink/colourless, +2
  • [Mn(H2O)6]3+, red, +3
  • MnO2, brown solid, +4
  • MnO4 2-, green, +6
  • MnO4-, purple, +7
28
Q

Give formulae, colour and oxidation state of common transition complexes/solutions/compounds of Fe

A
  • [Fe(H2O)6]2+, pale green, +2
  • [Fe(CN)6]4-, yellow, +2
  • [Fe(H2O)6]3+, yellow, 3+
  • [Fe(CN)6]3-, orange red, +3
  • [Fe(SCN)(H2O)5]2+, blood-red, 3+
29
Q

Give formulae, colour and oxidation state of common transition complexes/solutions/compounds of Co

A
  • [Co(H2O)6]2+, pink, +2
  • [Co(NH3)6]2+, pale brown, +2
  • [CoCl4]2-, blue, +2
  • [Co(H2O)6]3+, blue, +3
  • [Co(NH3)6]+3, yellow (may b dark brown due to mix of other Cr(III) complexes), +3
30
Q

Give formulae, colour and oxidation state of common transition complexes/solutions/compounds of Ni

A
  • [Ni(H2O)6]2+, green, +2
  • [Ni(NH3)6]2+, blue, +2
  • [Ni(CN)6]4-, yellow, +2
31
Q

Give formulae, colour and oxidation state of common transition complexes/solutions/compounds of Cu

A
  • Cu2O, reddish brown solid, +1
  • CuCl, white solid, +1
  • [CuCl2]-, colourless, +1
  • [Cu(H2O)6]2+, blue, +2
  • [Cu(NH3)4(H2O)2]2+, deep blue, +2
  • [CuCl4]2-, yellow, +2
32
Q

Explain ligand exchange

A

a stronger ligand can replace a weaker ligand fr cation complex in ligand exchange rxn
eg
when excess NH3(aq) added to Ni2+(aq), there is noticeable change in colour of resultant sol n fr green to blue

33
Q

How do we know if a ligand exchange reaction has occurred?

A

predict n is usually based on given observ n (ie colour change, dissolut n of ppt, etc.) or given relative stability const Kstab (LCP concept) of complex ion formed

34
Q

When dilute ammonia is gradually added to solution with Cu2+, a pale blue ppt forms, which dissolves on adding more dilute ammonia

Explain all the above transformation in terms of competing equilibria, writing equations for reactions which occur

A
  • when small amt NH3(aq) (base, provide OH- ion) added gradually, pale blue ppt Cu(OH)2 forms
    [Cu(H2O)6]2+ + 2OH- ⇌ Cu(OH)2 (s) + 6H2O —–(1)
  • in excess NH3, both NH3, OH- compete to combine w [Cu(H2O)6]2+
  • NH3 ligand replace H2O ligand in ligand exchange rxn to form dark blue complex [Cu(NH3)4(H2O)2]2+
    [Cu(H2O)6]2+ + 4NH3 ⇌ [Cu(NH3)4(H2O)2]2+ (aq) + 4H2O ——(2)
  • as conc of [Cu(H2O)6]2+ decrease in (2), eqm pos n in (1) shift left to increase [Cu(H2O)6]2+, so pale blue ppt Cu(OH)2 dissolves
35
Q

Explain heterogeneous catalyst with respect to transition elements

A
  • exist in diff phase fr rxt
  • transit n metal & their cpd r good heterogeneous catalyst bcos of availability of 3d, 4s e- for temporary bond form n w rxt
  • basic steps are:
    1. adsorpt n (NOT absorp n)
    2. activat n
    3. desorpt n
36
Q

Explain transition elements as catalyst, with example of production of ammonia via Haber Process using Fe catalyst

A
  1. N2, H2 molecules r adsorbed onto catalyst surface
  2. bonds break (activat n) btw N & N, H & H
  3. atoms re-arrange to form ammonia
  4. ammonia molecule leave catalyst surface (desorpt n); new N2, H2 molecule r adsorbed onto catalyst surface
37
Q

Explain transition elements as catalyst, with example of hydrogenation of alkenes on nickel surface

A

eg ethene
1. C2H4 & H2 molecule adsorbed onto catalyst surface
2. bonds break in H-H
3. H atom re-arrange form C2H6 (activat n)
4. C2H6 molecule leave catalyst surface (desorpt n)

38
Q

Explain transition elements as catalyst, with example of catalytic removal of oxides of nitrogen and unburnt hydrocarbons in exhaust gases from car engines

A
  • catalytic converter in exhaust system of motor vehicles speeds up the convers n of pollutants eg CO, NOx and unburnt hydrocarbons (CxHy) into harmless pdt eg H2O, CO2, N2

-removal of pllutant
1. NOx reduced to N2 by excess Co present (oxidised to CO2) w rhodium as heterogeneous catalyst
2NO + 2CO —> 2CO2 + N2

  1. unburnt hydrocarbons, CO oxidised to CO2 & H2O (& O2 reduced to H2O), with Pt, Pd catalysts
    CxHy + (x + y/4)O2 —> xCO2 + y/2 H2O
    2CO + O2 —> 2CO2
39
Q

Describe the mechanism for heterogeneous catalysis

A

Adsorpt n
- rxt molecule adsorbed onto catalyst surface thru form n of temporary bond (fr available 3d, 4s e-)

Activat n
- adsorpt n weaken covalent bond within rxt molecule, lowering Ea
- (kinetics) rxt molecules brought closer tgt, increasing surface conc of rxt, so rxn can occur btw rxt molecules more easily

desorpt n
- pdt formed diffuse away fr surface of catalyst

40
Q

Define homogeneous catalyst with respect to transition element

A
  • exist in same phase as rxt (usually aq)
  • transit n metal & their cpd r gd homogeneous catalyst bcos of their ability to exist in various OS, so facilitate form n of rxn intermediate via alternative pathway of lower Ea
41
Q

Describe mechanism for homogeneous catalysis, using example of S2O82-, I- reaction

A
  1. w/o catalyst,
    redox rxn S2O8 2- + 2I- –> 2SO4 2- + I2
    Ecell = Ered - Eox = 2.01-0.54 = +1.47V>0, so rxn feasible
    BUT, rxn kinetically not feasible due to high Ea, fr e-static repuls n btw -ve charge ions
    => in presence of transit n metal ion eg Fe2+ or Fe3+ acting as homogeneous catalyst, rxn is accelerated
  2. w catalyst (Fe3+)
    - step 1: Fe3+ react w I-
    2Fe3+ + 2I- —> 2Fe2+ + I2
    Ecell = 0.77-0.54 = +0.23V > 0, so rxn spontaneous
  • step 2: Fe2+ intermediate react w S2O8 2-
    2Fe2+ + S2O8 2- —> 2SO4 2- + 2 Fe3+
    Ecell = 2.01-0.77 = +1.24V>0, so rxn is spontaneous

Overall eqn: S2O8 2- + 2I- –> 2SO4 2- + I2 (still the same)

Both steps r spontaneous since opp charge ion involved, attract each other. Ea is lower, so rxn faster/kinetically feasible

42
Q

Name common reactions undergone by transition metal ions

A
  • ppt n rxn/soluble complex form n
  • ligand exchange rxn
  • redox rxn
  • hydrolysis (for aqua, H2O, ligand, complex ion w high charge density)

La Chimie H2 (25 decks)

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