Transition Elements Flashcards
Aufbau Principle
Electrons fill orbitals from the lowest energy orbital upwards
Pauli Exclusion Principle
No more than two electrons may occupy a single orbital and, if two electrons do occupy a single orbital, their spins must be opposite.
Hund’s Rule
Orbitals of a sub-shell (degenerate) must be occupied singly and with parallel spins before they can be occupied in pairs (with opposite spins)
Transition Element
A d-block element which can form one or more stable ions with a partially filled d subshell
Atomic Radius of Transition Elements
The atomic radii of the first-row transition elements in Period 4 are almost constant/relatively invariant
Ionisation Energies of Transition Elements
The first ionisation energies of the transition elements from Ti to Cu is almost constant/relatively invariant
Why do transition elements have variable oxidation states
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How do you calculate the highest possible oxidation state
This is primarily due to the close similarity in energy of the 3d and the 4s electrons, that both the 3d and the 4s electrons are available for bond formation (ionic or covalent)
No. of unpaired 3d-electrons + 4s electrons
Why do transitions elements form coloured compounds and ions
Catalyst
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How does a catalyst increases the rate of reaction
A substance which increases the rate of a reaction without itself undergoing any permanent change
A catalyst increases the rate of a reaction by providing an alternative pathway for the reaction, one with a lower activation energy than that of the uncatalysed reaction.
Process of heterogeneous catalysis
Diffusion
- Reactant molecules diffuse towards catalyst surface
Adsorption
- Reactant molecules become adsorbed onto the active sites of the catalyst surface through attractive forces.
Chemical Reaction
- Reaction has lower activation energy than the uncatalysed reaction
Desorption
- This is the reverse of adsorption. The product molecule eventually breaks free from the catalyst surface
Diffusion
- The product molecule diffuses away from the surface. The vacant active sites are now available for adsorbing other reactant molecules
What is a complex
A complex contains a central metal atom or ion linked to one or surrounding ions/molecules (ligands) by coordinate bond. If the species carries an overall charge
What is a ligand
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What do ligands act as
Is an ion or molecule which contains at least one atom bearing a lone pair of electrons which can be donated into a low-lying vacant orbital of a central metal atom/ion, forming a coordinate/covalent bond, resulting in the formation of a complex.
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Ligands act as Lewis bases (electron pair donors)
Condition required for complex formation
(1) The presence of ligands to donate electron pairs to form coordinate bonds
(2) The presence of a central metal ion/atom capable of accommodating the lone pair of electrons in its low-lying vacant orbitals to form a coordinate bond.
Why is an aqueous solution of FeCl3 acidic?
Due to its high charge and small size, the Fe3+ ion has high charge density and is hence strongly polarising. It distorts the electron cloud of the H2O molecules bonded to it, weakening the O-H bonds and enabling these H2O molecules bonded to it to become proton donors. The free water molecules in the solution act as bases (Bronsted Lowry Bases are proton acceptors) and the following equilibrium is established:
[Fe(H2O)6]3+ + H2O -> [Fe(OH)(H2O)5]2+ + H3O+
The Fe3+ ion is consequently said to undergo appreciable hydrolysis in aqueous solution. The slight excess of H3O+ ions in the solution causes the solution to be acidic.
Result of adding Na2CO3 to an aqueous solution containing Fe3+, Cr3+, & Al3+
Red - brown ppt (Fe3+)
Green ppt (Cr3+)
White ppt (Al3+)
Upon addition of Na2CO3, effervescence is observed as CO2 is produced as result of the reaction between the carbonate anion and the hydronium ion.
[Fe(H2O)6]3+ + H2O -> [Fe(OH)(H2O)5]2+ + H3O+
The consumption of hydronium ions causes the equilibrium position of reaction above to shift right. With more carbonate ions added, and hence more hydronium ions removed, the equilibrium position of subsequent reactions are also forced to shift right. Consequently, a (colour) ppt of (complex: all 3+) is obtained together with the evolution of CO2.
Overall reaction:
2[Fe(H2O)6]3+ + 3CO32- -> 2[Fe(OH)3(H2O)6] + 3CO2 + 3H2O
