2.4 Transition Metals Flashcards
Define a transition metal
An element which forms at least one stable ion with an incomplete d subshell.
Where are transition metals located in the periodic table ?
In the d subshell (between g2 and g3)
What are some physical characteristics of transition metals ?
•Good conductors of heat and electricity
•High mp and bp
•Shiny
•Low reactivity
What are the characteristic chemical properties of transition metals ?
•Variable oxidation states
•Form coloured compounds in solutions
•Good catalysts
•Form complex ions.
Define the term ‘complex ion’
A transition metal is central in a molecule surrounded by ligands (other molecules/ions) that are co-ordinate bonded to it.
Give three examples of transition metals catalysts and the reactions
Iron - Haber process
Vanadium oxide (V2O5) - Contact process
MnO2 - Decomposition of H2O2.
From what subshell do transition metals lose electrons first from when forming ions ?
4s.
Define the term ligand
•An ion or molecule with at least one lone pair of electrons
•Donates them to a transition metal to form a co-ordinate bond and thus a complex ion.
Define the term mono/unidentate ligand
A ligand that forms one co-ordinate bond to the central transition metal in a complex (one lone pair to donate).
Define the term bidentate ligand
A ligand that forms two co-ordinate bonds with a central transition metal in a complex ion (two lone pairs to donate).
Define the term multidentate ligand
A ligand that forms three or more co-ordinate bonds with a central TM ion in a complex ion.
Give some examples of common monodentate ligands
•Cl-
•H2O
•NH3
•CN-
What is the formula for an ethanedioate ion ? How many co-ordinate bonds can it form in a complex ?
•C2O4 2-
•Forms two co-ordinate bonds, bidentate
—
—
How many co-ordinate does ETDA 4+ form ?
6.
Define the term co-ordination number
The number of co-ordinate bonds a transition metal has made with surrounding ligands in a complex ion.
What is the Chelate effect ?
Chelate complexes with multidentate ligands are favoured over monodentate ligands or ligands that form fewer co-ordinate bonds per molecule.
Explain the chelate effect in terms of entropy and the reaction that is occurring
•The number of molecules increases when multidentate ligands displace ligands that form fewer co-ordinate bonds per molecule
•This gives a significant increase in entropy
•The Gibbs free energy change is <0 which makes it a feasible reaction
•Therefore a more stable complex ion is formed.
What ion is typically formed when a transition metal dissolves in water ?
•An aqua ion
•6 H2O ligands form around the central ion
•Octahedral complex ion shape.
If a transition metal has two ligands in a complex ion what is it’s shape ?
Linear.
If a transition metal has 4 ligands in a complex ion what is its shape ?
Tetrahedral
Name an exception to the rule that a complex ion with 4 ligands has a tetrahedral shape
Platin (platinum 2+) forms square planar molecules.
What shape is a complex ion if it has 6 ligands ?
Octahedral
How can complex ions display cis-trans isomerism ? What shapes of ions does this apply to ?
•Ligands can differ in the way they are arranged in space
•When two of the same ligand are on opposing sides of the central ion the complex is a cis isomer
•When two of the same ligand are on the same side of the central ion the complex is a trans isomer
•This applies to square planar and octahedral complex ions.
What conditions are needed for a complex ion to display optical isomerism ?
•Typically applies to octahedral molecules with two or more bidentate ligands
•This means the mirror images will not superimpose.
What happens to Co2+, Cu2+ and Fe3+ ‘s co-ordinate numbers when Cl- ligands replace NH3 or H2O ligands ?
It decreases from 6 to 4 as Cl- is a much larger ligand than H2O or NH3.
What is haem - it’s metal ion, co-ordination number and ligands ?
•A molecule which makes up proteins
•It has an Fe2+ central ion
•It has a coordination number of 6
•4 of these bonds form to porforin, one forms to nitrogen and one forms to O2.
How does haemoglobin transport oxygen ?
•O2 forms a weak co-ordinate bond with the Fe2+ ion
•It is then transported around the body
•The bond breaks when the haemoglobin reaches the cell and O2 is released.
Why is CO monoxide toxic ?
•CO coordinately bonds to the Fe2+ ion of Haemoglobin and is a favoured ligand
•This means it bonds more strongly than just O2 and therefore stops O2 from being transported around the body.
Why are transition metal compounds coloured ?
•TMs have partially filled d subshells
•In compounds (when ligands have bonded to the ion) the d subshell splits into two energy levels
•Electrons can gain a precise amount of energy from a photon, become excited and move to a high energy level
•The energy of the photon = difference between levels / gap in energy
•The energy of the photon is released to the frequency of the light
•The photon which is absorbed is missing from the light which is then reflected, we see the combination of all remaining frequencies.
How do you calculate ΔE from f and / or gamma?
ΔE=hf=hc/gamma