Transition Elements Flashcards
(42 cards)
Define transition element
a d-block element that form at least 1 stable ion w PARTIALLY-filled d subshell
Name exceptions electronic configuration of transition elements
- 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
Why is Sc and Zn not classified as transition elements?
- 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)
Describe chemical and physical properties of transition elements
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
Describe how atomic and ionic radius of transition elements change across series
- 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
Describe how ionisation energy of transition element series change in general
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
Describe anomalies for ionisation energy of transition element series
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-
Explain why transition elements have a smaller atomic radii and a higher first ionisation energy than s block elements such as Ca
- 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
Explain hardness and density of transition elements
- 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
Explain melting and boiling points of transition elements
- 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
Explain electrical and thermal conductivity of transition elements
- 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
Explain why transition elements (Ti to Cu) have variable oxidation states
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
Explain standard electrode potentials of transition elements
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
Define transition metal complex
complex containing central metal atom/ion attached to ligands thru dative bond
eg [Cu(H2O)6]2+
Define ligand
molecule or anion containing at least 1 lp e- available to form dative bond w central metal atom/ion
Define coordination number
no. of dative bonds each central metal atom/ion can form w its ligands
Explain why transition element ions can form complex ions
- 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
Define monodentate ligand, bidentate ligand and polydentate ligand
- 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)
Describe shapes of transition element complexes
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-
What to take note about drawing transition element complexes?
- 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
Explain, in terms of d orbital splitting, why transition element complexes are usually coloured
- 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
Explain why d orbitals in an octahedral transition element complex split into two different energy levels
- 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
Roughly explain colour wheel for transition element complex
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)
What affects colour of transition element complexes
- 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
- 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
