Chapter 24 Transition elements Flashcards
Define transition element
A d-block element which forms one or more stable ions with incomplete d orbitals.
State the 4 properties of transition elements
1) They have variable oxidation states.
2) They behave as catalysts.
3) They form complex ions.
4) They form coloured compounds.
Why do transition elements have variable oxidation states?
3d and 4s sub-shells have similar energy.
Why do transition elements act as catalysts?
They have more than one stable oxidation state, have vacant d orbitals that are energetically accessible, and can form dative bonds with ligands.
Why do transition elements form complex ions?
They have vacant d orbitals that are energetically accessible.
Define complex ion
A molecule or ion formed by a central metal atom/ion surrounded by one or more ligands.
Define ligand
A species that contains a lone pair of electrons that forms a dative covalent bond to a central metal atom/ion.
Define monodentate ligand
A molecule or ion that donates one lone pair and forms one dative bond with a central metal atom/ion.
Define bidentate ligand
A molecule or ion that donates two lone pairs and forms 2 dative bonds with a central metal atom/ion.
Define polydentate ligand
A molecule or ion that donates more than two lone pairs and forms more than 2 dative bonds with a central metal atom/ion.
5 examples of monodentate ligands
H20, OH-, NH3, Cl-, CN-.
2 examples of bidentate ligands
C2O4 -2, ethanedioate ion (Oxalate ion/Oxy) AND 1,2-diaminoethane (en).
Example of polydentate ligand
EDTA 4- (Hexadentate)
Define coordination number
The number of dative covalent bonds the central metal atom/ion makes.
Cu²⁺(aq) + excess NH₃(aq) reaction
Cu(OH)₂(H₂O)₄ + 4NH₃(aq) —> [Cu(NH₃)₄(H₂O)₂]²⁺(aq) + 2OH-(aq) + 2H₂O(l)
Cu²⁺(aq) + Cl-(aq) reaction
[Cu(H₂O)₆]²⁺(aq) + 4Cl-(aq) ⇌ [CuCl₄]²⁻(aq) + 6H₂O(l)
Co²⁺ (aq) + excess NH₃(aq) reaction
[Co(H₂O)₆]²⁺(aq) + 6NH₃(aq) —> [Co(NH₃)₆]²⁺(aq) + 6H₂O(l)
Co²⁺(aq) + Cl-(aq) reaction
[Co(H₂O)₆]²⁺(aq) + 4Cl-(aq) —> [CoCl₄]²⁻(aq) + 6H₂O(l)
[Cu(H₂O)₆]²⁺(aq) colour
Blue solution
Cu(OH)₂(H₂O)₄ colour
Pale blue precipitate
[Cu(NH₃)₄(H₂O)₂]²⁺(aq) colour
Dark blue solution
[CuCl₄]²⁻(aq) colour
Yellow solution, but when formed at dynamic equilibria the observation is green (blue+yellow).
[Co(H₂O)₆]²⁺(aq) colour
Pink solution
Co(OH)₂(H₂O)₄ colour
Pale blue precipitate
[Co(NH₃)₆]²⁺(aq) colour
Brown solution
[CoCl₄]²⁻(aq) colour
Blue solution
Shape and bond angle of complex ion with 2 dative covalent bonds?
Linear 180 degrees.
Shapes and bond angles of complex ion with 4 dative covalent bonds?
Tetrahedral 109.5 degrees OR Square planar 90 degrees.
Shape and bond angle of complex ion with 6 dative covalent bonds?
Octahedral 90 degrees
Shape of [CuCl₄]²⁻(aq)?
Tetrahedral.
Shape of Cu(OH)₂(H₂O)₄ and [Cu(H₂O)₆]²⁺(aq)?
Octahedral
Shape of cis-platin/trans-platin?
Square planar
Shape of [Ni(CN)₄]²⁻(aq)?
Square planar
Requirements for geometrical (cis-trans) isomerism in complex ions
1) Coordination number 4 square planar shape, with 2 different types of ligands.
2) Coordination number 6 octahedral shape, with 2 different types of ligands.
Requirements for Optical isomerism in complex ions
Coordination number 6 octahedral shape, with either
1) All ligands are bidentate.
2) 2 bidentates + 2 monodentates.
3) All 6 are different types of monodentates.
Define degenerate orbitals
There are five d orbitals in an isolated transition element atom or ion. An isolated transition element is one that is not bonded to anything else. These d orbitals are all at the same energy level (they are equal in energy) and are therefore said to be degenerate orbitals.
Define non-degenerate orbitals
The dative bonding from the ligands causes the five d orbitals to split into two sets. These two sets are not equal in energy and are described as being non-degenerate orbitals.
Splitting of 3d orbitals in an octahedral complex
The 3dx2-y2 and 3dz2 non-degenerate orbitals are slightly higher in energy than the 3dyz, 3dxz and 3dxy non-degenerate orbitals
Splitting of 3d orbitals in a tetrahedral complex
The 3dyz, 3dxz and 3dxy non-degenerate orbitals are slightly higher in energy than the 3dx2-y2 and 3dz2 non-degenerate orbitals
Why do complex ions have colours?
Transition element complexes absorb the frequency of light which corresponds to the exact energy difference (ΔE) between their non-degenerate d orbitals.
The electron uses the energy from the light to jump into a higher, non-degenerate energy level.
This is also called electron promotionThe frequencies of light which are not absorbed combine to make the complementary colour of the complex.
Why do different complex ions have different colours?
ΔE between their non-degenerate d orbitals differs. So, the light frequency absorbed differs, giving off 2 different colours.
Define Kstab
The equilibrium constant for the formation of the
complex ion in a solvent from its constituent ions or molecules.
If Kstab is larger, that means the complex ion is…
More stable and the reaction will happen and the complex ion will be formed.
