H2 Chemistry 23 - Transition elements

d-block element, forms 1 or more stable ions w/ partially filled d-subshell of e^-

in complex, 5 d orbitals split into 2 diff sets of energy levels(d orbital splitting) >

a d e^- promoted from a lower energy d orbital to a higher energy d orbital by absorbing energy(wavelength) of light that corresponds to specific colour(d-d transition) >

light not absorbed is seen as colour of complex

across period, no. of protons increase, nuclear charge increases >

e^- added to inner 3d sub-shell, shielding effect increases >

increasing nuclear charge cancels out increasing shielding effect >

nuclear attraction on outermost e^- relatively similar

effect of increasing nuclear charge cancels out increasing shielding effect by increasing inner 3d e^- >

nuclear attraction on outermost 4s e^- to be removed relatively similar

TE greater mass than s-block elements in same period >

TE relatively smaller atomic radii >

thus TE have > closely packed structures >

results in TE having > density than s-block elements

(density=mass/volume proportional RAM/atomic radius)

> energy required to overcome stronger metallic bonds b/w TE atoms & mobile delocalised valence e^- >

TE > delocalised mobile valence e^- from 3d, 4s orbitals(small diff) >

TE atoms > charge densities(> charge, < radii)

small energy diff b/w 3d, 4s >

both 3d, 4s e^- can behave as valence e^- >

variable no. of e- from 3d, 4s orbitals involved in bonding, forms stable ions/compounds w/ diff O.S.

very high ionisation energies required to form them >

due to very high charge, small density -> cations very high charge density, very high polarising power to polarised e- cloud of surrounding species to large extent, bonding becomes covalent >

in (aq) solution, these cations polarize adjacent co-ordinated H₂O molecules extensively -> CrO₄^2-, MnO₄^-

E^o_cell > 0, redox reaction energetically feasible >

redox reaction likely to occur

anion/molecule w/ at least 1 LP of e^- to form dative bond w/ central metal atom/ion

high charge density of cations to attract LP of e^- from ligands >

presence of energetically accessible vacant d orbitals to accept LP of e^- from ligands

net charge on complex; sum of oxidation no. of central metal ion & total charges of ligands surrounding it

co-ordination number; total no. of dative bonds formed b/w TE & ligands in complex

high charge density of M³⁺ >

M³⁺ polarises H₂O ligand >

breaks O-H bond of H₂O ligand >

releases H⁺, makes solution acidic

[M(H₂O)₆]³⁺ partially hydrolysed -> [M(H₂O)₅(OH)]²⁺ + H₃O⁺

stronger ligands displaces weaker ligands in ___ complex by forming stronger dative bond w/ M^x+, giving > stable ___ complex

O₂ molecule reversibly bonded to Fe²⁺ in each haem group by dative bond>

allows Hb to carry O₂ in blood from lungs to other parts of body >

1 Hb molecule bind to 4 molecules of O₂, forms oxyhaeamoglobin >

CO poisoning, stronger CO ligand displaces weaker O₂ ligand by forming stronger dative bond w/ Fe²⁺ in haem group, forms > stable carboxyhaemoglobin complex >

Hb unable to transport O₂ to cells

can be treated with high [O₂];

causes POE to shift right increasing [Hb(O₂)₄], decreases [Hb] >

lower [Hb] causes POE to shift left, decreasing [Hb(CO)₄], releases CO

ligands approach metal ion along x,y,z axes >

d orbitals w/ lobes along axes(d_x²-y², d_z²) greater electrostatic repulsion w/ LP of incoming ligands, higher energy than d orbitals w/ lobes b/w axes >

ligands present, 5 d orbitals of central metal ion split into 2 sets of different energies

4 ligands approach metal ion b/w axes >

e- in 3d_xy, 3d_xz, 3d_yz orbitals greater electrostatic repulsion from LP of ligands >

3d_xy, 3d_xz, 3d_yz higher energy than 3d_x²-y², 3d_z²

energy gap = hc/(wavelength) = h(frequency); h=Plancks' constant, c=speed of light

larger energy gap leads to absorption of shorter wavelength, smaller energy gap leads to absorption of longer wavelength

diff no of e^- in d orbitals result in diff degree of repulsion >

diff energy gap, wavelengths of light absorbed diff >

change in O.S of TE, redox occurred, colour change observed

diff ligands, diff capacities of splitting d orbitals >

diff magnitude of energy gap >

larger energy gap, higher freq of light absorbed, shorter wavelength absorbed -> longer wavelength observed

TE act as heterogenous catalysts, partially-filled 3d orbitals available;

3d e^- available for donation to rxt molecules

vacant orbitals available to accept e^- pairs from rxt molecules

catalyst adsorbs rxt molecules on its surface, uses partially-filled 3d orbitals, form weak bonds w/ rxt molecules >

weakens bonds in rxt molecules, provides alternative pathway of < E_a, surface [rxt] increases, rate of rxn increases >

pdt formed desorbs from catalyst surface, available for adsorption of new rxt molecules

TE act as homogenous catalysts due to ability to vary oxidation states since 3d, 4s orbitals have similar energies, ease of interconversion b/w diff O.S. provides alternative rxn pathway of < E_a