Transition metals Flashcards
What are transition metals?
one that forms at least one stable ion with a PARTIAlLLY filled d-shell of electrons.
What are the characteristics of transition metal?
- variable oxidation states
- formation of coloured ions
- catalytic activity
- complex formation
Why isn’t zinc a transition metal?
because it’s ion zn^2+ has a full d sub shell not partially filled
What does a “complex” mean?
a central metal atom or ion surrounded by ligands linked by coordinate bonds
What is a ligand
a molecule or ion that forms a coordinate bond with a transition metal by donating a pair of electrons.
What is the coordination number?
the number of co-ordinate bonds to the central metal atom or ion
What is the chelate effect?
Bidentate and multidentate ligands replace monodentate ligands from complexes. The complexes formed from multidentate ligands are more stable due to an increase in particles resulting in greater entropy
What are chelates?
complexions with polydentate ligands
What are examples of bidentate ligands (draw the structure)
What is an example of a multidentate? (draw the structure)
What does cis and trans mean?
- When two groups are on the same side, they are cis.
- When two groups are on opposite sides, they are trans.
When does E/Z isomerism occur in a complex?
This can occur in octahedral and square planar that have monodentate ligands
When does optical isomerism occur in a complex?
when octahedral complexes have three bidentate ligands
When can ligand substitution reactions be reversed?
when the new complex ion is less than or equally stable as the original one
What is haem and what is globin? Describe the structure of haemoglobin.
Haem is an iron(II) complex that is hexa-coordinated
Four of the co-ordinate bonds come from four nitrogen atoms from the same molecule co-ordinate around Fe2+ to form a circle. This part of the molecule is called haem.
The other two co-ordinate bonds come from a protein called globin, and either an oxygen or a water molecule - so the complex can transport oxygen to where it’s needed, and then swap it for a water molecule
How does the structure of haemoglobin help transport oxygen around the body?
- In the lungs, where the oxygen concentration is high, an oxygen molecule substitutes the water ligand and bonds co-ordinately to the Fe (ll) ion to form oxyhaemoglobin, which is carried around the body in the blood.
- When the oxyhemoglobin gets to a place where oxygen is needed, the oxygen molecule is exchanged for a water molecule. The haemoglobin then returns to the lungs and the whole process starts again.
How does carbon monoxide prevent oxygen being transported around the body?
- The haemoglobin swaps its water ligand for a carbon monoxide ligand, forming carboxyhaemoglobin.
- Carbon monoxide is a strong ligand and doesn’t readily exchange with oxygen or water ligands, meaning the haemoglobin can’t transport oxygen any more.
What are the two different types of catalyst?
Heterogenous = catalysts which are in a different phase from the reactants
Homogenous = same phase as reactants
Why are transition metals good catalysts?
Catalysts work by changing oxidation states and transition metals can change oxidation states very easily.
How do catalysts work?
They provide an alternative route with a lower activation energy - this causes MANY more particles to have E>Ea, so a larger proportion of collision are successful
What is the difference between absorption and adsorption?
- Adsorption iswhere the reactant molecule sticks to the surface of the catalysts
- Absorption where the molecule is taken up.
What are examples of heterogeneous catalysts?
- V2O5 in the Contact process.
- Fe in the Haber process.
- Platinum/rhodium/platinum in the catalytic convertor
What are examples of homogeneous catalysts?
- Aluminium chloride in acylation
- Cl radicals in the destruction of the ozone layer
- Fe (3+) in the oxidation of iodide ions by peroxidisulphate (VI) ions
- The autocatalysis by manganese (II) ions of the oxidation of ethanedioate ions by manganate (VII) ions
How do heterogeneous catalysts work?
- adsorption
- reaction
- desorption