Topic 15: Transition Metals Flashcards
What are transition metals
Transition metals= d block elements that form one or more stable ions with incompletely filled d orbitals.
They are hard solids w high mpts, can act as catalysts, from coloured ions, and form ions with different ox.numbers.
Why are scandium and zinc not transition metals?
Scandium loses both of its 4s e- and its only 3d e- to form Sc3+. Zn loses both of its 4s e- and none of its 3d e- to form Zn2+. Bc these elements form 1 ion each w no incompletely filled d orbitals they are not transition metals.
Describe the relationship between transition metals and oxidation number
Each transition metal can lose a variable number of e-, so forms ions with diff ox.numbers.
Transition metal ions w high ox.numbers usually contain an electroneg element like oxygen.
From Fe to Cu across the period hay increased nuclear charge. e-s are attracted more strongly so less likely to bond. Therefore ions w higher ox.numbers are less common across a period.
what are Ligands?
Ligands are the electron rich species that form dative covalent bonds with the central metal ion.
Transition metals have smaller radii, so they attract electron rich species more strongly, including aq water molecules.
What is a complex ion? Why do transition metals regularly form complex ions?
A complex ion has ligands attached to a central metal cation by a dative covalent bond.
Cations which form complex ions must have: high charge density to attract e- from ligands, and empty low energy orbitals to accept the lone e- pair from the ligands.
Metal d-block cations are small, have a high charge density and have empty low energy 3d and 4s orbitals. So they form complex ions readily.
What is coordination number?
The number of lone e- pairs a cation can accept/ total no of dative bonds around the metal ion.
Coordination number is not the number of Ligands! eg EDTA forms six coordinate bonds so the coordination number is six, but it is one ligand
How many dative bonds can 1 ligand form?
Ethanedioate (C2O42-) and 1,2-diaminoethane donate 2 lone pairs per ligand and are bidentate.
Ligands such as H2O, Cl- and CN- form only one dative covalent bond per ligand (monodentate).
EDTA4-, is HEXAdentate.
Draw the following: [Fe(H2O)6]2+ [Cr(NH3)6]3+ [Cu(NH3)4(H2O)2]2+
Draw the following multi dentate ligand complexes:
[Fe(C2O4)3]3- [Cr(H2NCH2CH2NH2)3]3+ [Cu(edta)]2
How do you determine the shape of complex ions?
2-coordinate complexes are generally linear, and are formed w Ag+ ions.
Pt ions form square planar complexes. Coordination number=4, bond angle 90°
Cl- and other large ions form tetrahedral complexes. Coordination number=4, bond angle 109.5°
Most other transition metal complexes are octahedral w coordination number 6, bond angles 90°
Draw [CoCl4]2- and explain its shape
What must occur for an ion to be coloured?
If the ion is to be coloured:
there must be splitting of the d-orbitals. This only happens in the presence of ligands so only complex ions are coloured. Anhydrous ions don’t have split d-orbitals, so cannot aborb light in the visible spectrum so are white.
d-orbitals must be partially filled. If empty, then no hay e- which can be excited into the higher energy d-orbitals, ions will be colourless. If the d-orbitals are full then no hay empty orbitals where the e-s can be excited, ions will be colourless.
Describe and explain why the copper 2+ ion is coloured
The copper ion has an incompletely filled d orbital, which splits into different energy levels by ligands.
The electron from the lower level absorbs light from the visible spectrum. The e- is excited and jumps from the lower energy to the higher energy level
In Cu2+, the SMALL energy level difference means LOW Hz radiation is absorbed from the red end of the spectrum. So blue light is transmitted.
Explain change in oxidation number of iron after exposure to air.
After exposure to air iron goes from pale green in aq solution to brown. Ox.number increases from +2 to +3.
The type and number of ligands dont change.
Formula for both: [Fe(H20)6]2+ and [Fe(H20)6]3+
Describe the reaction between sodium hydroxide and copper sulphate solution.
When aq Na0H is added to aq CuS04, a pale blue solution forms a blue ppt:
[Cu(H20)6]2+ + 2OH- –> [Cu(H20)4(0H)2] + 2H20
This is not ligand exchange, but an acid-base reaction; the 2 0H- ions removed H+ from 2 water ligands and converted them to water molecules. The 2 water ligands that lost H+ are now 0H- ligands.
This is amphoteric bc it’s reversible– when acid is added to the blue ppt, H+ from the acid reacts with the OH- ligands and converts them to water molecules.
