20. Transition Elements Flashcards
(18 cards)
define transition element
d-block element
can form 1 or more stable ions with a partially filled d-subshell
define ligand
a molecule or anion with at least 1 lone pair of e to form a dative bond with the transition metal atom/ion
def complex ion
a species which contains a central metal atom/ion surrounded by molecules/anions which form coordinate ions to the metal centre
def coordination number
the number of coordinate bonds around the central metal ion/atom in the complex
Exp why the first IE // atomic radii of transition metals are relatively invariant (aka similar)
- no. p inc, nuc charge inc
- each additional e is added to the penultimate (2nd last) 3d subshell
- shielding eff inc as the presence of 3d orbitals shield the 4s e from nu attraction
- eff nu charge almost constant
- attraction btw nu and outermost e/shell remains almost constant
- energy req to remove the e is relatively invariant // relatively same ionic radii
Exp why density of TM is high
- smaller atomic radii, smaller volume
- larger mass per unit vol
exp why mp of TM is so high
- 3d and 4s e are close in energy, avail to contribute to sea of delocalised e
- more energy req to break stronger metallic bonds
Exp why theres a ΔE
- Ligands approach along x,y,z axes
- e in in d-orbitals and ligands repel eo –> orbitals hav higher energy lvl than those in gas-phase ion
- dxy, dyz, dxz have lobes directed btw axes
- dx²-y², dz² hav lobes directed along the axes pointing towards the ligands
- e in dx²-y², dz² exp stronger repulsion
Explain why transition metals are coloured
In the** presence of ligands**, the partially filled 3d orbitals to split into 2 energy lvls w a small energy gap ΔE.
An e in the lower energy d-orbital absorbs energy in the visible spectrum corr to ΔE and becomes excited to a vacant higher energy d-orbital. (d-d transition)
Unabsorbed wavelengths are transmitted, colour observed is complementary to the colour absorbed
Exp 2 reasons why some transition metals are not coloured
- No e in the d orbitals to absorb energy in the visible spectrum corr to ΔE.
- d-orbitals fully occupied, no vacant d-orbitals at the higher energy lvl to for the excitation of e from the lower energy lvl.
hence d-d transition is not possible
Exp how TM work as a heterogeneous catalyst
Adsorption Theory
Possess partially filled d subshell
* d orbitals avail for formation of weak temp bonds w the reactant mol
* energetically low-lying vacant d orbitals can be used to accommodate e pairs from reactant mol
Exp how TM work as a homogeneous catalyst
can exhibit variable OS
What are the Cu compounds + colour
- [Cu(H₂O)₆]²⁺ blue sol
- [Cu(OH)₂] pale blue ppt
- [Cu(NH₃)₂(H₂O)₄]²⁺ deep blue sol
- CuCO₃ green ppt
- CuCl₄²⁻ yellow sol (w conc HCl)
- CuCl/CuI white ppt
Eqn for sodium thiosulfate and Cu
- 2 Cu²⁺ + 4I⁻ –> 2CuI + I₂
white ppt in brown sol
(looks like cream ppt) - 2S₂O₃²⁻ + I2 –> S₄O₆²⁻ + 2I⁻
brown sol turns colourless
white ppt remains
What are the Fe²⁺
compounds + colour
- [Fe(H₂O)₆]²⁺ pale green
- Fe(OH)₂ green
> Fe(OH)₂ w O₂ in air to Fe(OH)₃ - FeCO₃ green ppt
- funny CN one is dark blue ppt
What are the Fe³⁺
compounds + colour
- [Fe(H₂O)₆]²⁺ pale green//yellow
- Fe(OH)₂ green//red-brown ppt
- [Fe(SCN)(H₂O)₅]²⁺ blood red
- funny CN one is dark blue ppt
What are the Cr compounds + colour
CrO₄²⁻ + 2
- [Cr(H₂O)₆]³⁺ green sol
- CrO₄²⁻ yellow sol
- Cr₂O₇²⁻ orange sol
CrO₄²⁻ + 2H⁺ –> Cr₂O₇²⁻ + H₂O
What are the Mn compounds + colour
- [Mn(H₂O)₆]²⁺ pale pink
- Mn(OH)₂ off-white ppt
> Mn(OH)₃ brown ppt
{Mn(OH)₂ w O₂ in air} - MnCO₃ white ppt
………………………………………………… - MnO₂ brown ppt (alkali)
- MnO₄⁻ purple
