5.3.1 Transition Elements
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How are transition element atoms and ions formed?
• 4s orbital fills before 3d orbitals to form atoms • 4s orbital empties before 3d orbitals to form ions
What are the exceptions to the expected electron configuration?
• Cr = 3d5 4s1 • Cu = 3d10 4s1 • Additional stability due to half filled and fully filled subshells
What is a transition element?
D-block elements that form at least one ion with a partially filled d-orbital
Which elements are and are not transition metals?
• Ti to Cu are transition metals • Sc and Zn are not transition metals
Why are Sc and Zn not transition metals?
• Zn only forms Zn2+ by losing 4s electrons to form full d-orbitals • Sc only forms Sc3+ by losing 4s electrons and 1 3d electron to form empty d-orbitals
What are the 4 properties of transition metals?
• Formation of coloured ions • Existence of variable oxidation states • Elements and compounds can act as catalysts • Formation of complex ions
What is the trend in oxidation states across the transition metals?
• Number of oxidation states increases across the series to Mn and then decreases • All form compounds with a 2+ oxidation state
What are examples of transition element catalysts?
• Fe (s) is a catalyst for the Haber process • N2 (g) + 3H2 (g) ⇌ 2NH3 (g) • V2O5 (s) acts as a catalyst for the contact process • 2SO2 (g) + O2 (g) ⇌ 2SO3 (g)
What is a ligand?
A molecule or ion with a lone pair that forms a coordinate bond
What is a complex ion?
Metal ion with ligands coordinately bonded to it
What is the coordination number?
The number of coordinate bonds attached to the central metal ion from ligands
What is a unidentate ligand?
• Forms one coordinate bond • Donates 1 pair of electrons E.g. H2O, NH3, OH-, Cl-, CN-
What is a bidentate ligand?
• Forms 2 coordinate bonds • Donates 2 lone pairs E.g. NH2CH2CH2NH2, C2O42-
When does a tetrahedral complex ion form?
• Coordination number of 4 • Due to large ligands • 109.5° bond angle E.g. [CuCl4]2-
When does a square planar complex ion form?
• Coordination number of 4 • Most common in Pt2+ complexes • 90° bond angle E.g. [PtCl4]2-
When does an octahedral complex ion form?
• Coordination number of 6 • Most common shape • 90° bond angle E.g. [CU(H2O)6]2+
How does cis-trans isomerism form in square planar complexes?
• Square planar complexes with 2 identical ligands attached to central metal ion • Cis isomer has identical ligands adjacent at 90° • Trans isomer has identical ligands opposite at 180°
How does cis-trans isomerism form in octahedral complexes?
• Octahedral complexes with 4 of one type of ligand and 2 of another • Or two bidentate ligands
How does optical isomerism form in octahedral complexes?
• Octahedral complexes with 2 or more bidentate ligands • Form non-superimposable mirror images
What is an example of an isomer?
• Cis-platin [Pt(NH3)2Cl2] • Anti-cancer drug • Bind to DNA to prevent cell division
What is the overall equation for ligand substitution in Cu with NH3?
[Cu(H2O)6]2+ (aq) + 4NH3 (aq) -> [Cu(NH3)4(H2O)2]2+ (aq) + 4H2O (l) - Pale blue solution to dark blue solution
What is the equation for ligand substitution in Cu with NH3 dropwise?
[Cu(H2O)6]2+ (aq) +2NH3 (aq) -> [Cu(OH)2(H2O)4] (s) + 2NH4+ (aq) - Pale blue solution to pale blue precipitate
What is the equation for ligand substitution in Cu with excess NH3?
[Cu(OH)2(H2O)4] (s) + 4NH3 (aq) -> [Cu(NH3)4(H2O)2]2+ (aq) + 2H2O (l) + 2OH- (aq) - Pale blue precipitate dissolves to dark blue solution
What is the equation for ligand substitution in Cu with excess HCl?
[Cu(H2O)6]2+ (aq) + 4Cl- (aq) ⇌ [CuCl4]2- (aq) + 6H2O (l) - Pale blue solution to yellow solution - Octahedral to tetrahedral - Green solution form sas an intermediate due to mixing