3.4 - The D-block/transition elements Flashcards
What is a transition element?
A transition element is a d-block element which forms one or more stable ions with incomplete d-orbitals
Why are Sc and Zn not counted as transition metals?
They do not have incomplete d-orbitals and so are not considered transition metals
How do you work out the maximum oxidation state for a transition metal?
The number of 4s electrons plus the number of unpaired 3d electrons
What are orbitals?
Orbitals are interpretations of mathematical equations which determine the probability of finding an electron in a given space.
Describe dxy, dz and dyz
Each have 4 lobes in the same plane as eachother, 90* apart, each lobe is inbetween the 2 axis on that plane
Describe dx2-y2
Has the same shape as the previous 3 orbitals but the lobes lie directly on the x and y axis
Describe dz2
2 lobes which lie on the z axis with a ring or doughnut around the middle
How does the melting point of transition metals differ from calcium and why?
Transition metals have a higher melting point than calcium
- in calcium the 4s electrons are involved in the metallic bond which holds the structure together
- in scandium onwards 3d electrons are also involved in the metallic bond
- this creates metallic bonds which are stronger and hence results in a higher melting point
What happens to densities as you move across the d-block?
AS you move across the d-block the atomic radius decreases due to the increasing nuclear charge pulling the outer electrons closer to the nucleaus (the additional electrons filling up the nucleus)
- the size is smaller but the density is greater across d-block
- transition metals are more dense than calcium
What are ligands?
Ligands are bases with a lone pair of electrons that forms a dative bond to a central metal atom/ion (they are attracted to metal ions)
What are complex ions?
A complex ion is a molecule or ion formed by a central metal atom surrounded by one or more ligands
Why do metals seek out ligands?
The positive metal ion is stablised by the ligands and so an ion will make as many bonds with as many ligands as it able (up to 6)
What is a coordination number?
The number of coordinate bonds being formed to the metal ion (most commonly 2,4,6)
What is a octahedral complex?
Six bonds attached to a central atom creates an octahedral complex to minimise repulsion between the bonding pairs
What is a tetrahedral complex?
If the ligand is especially large than there will not be room to fit 6 ligands (due to steric hinderance)
What is a square planar complex\?
Platinum is an exception to complexes with a cordination number of 4 (which normally are tetrahedral). There are 90* between each of the dative bonds
What is a linear complex?
Forms with 2 ligands, coord number of 2, an example is the active species in the tollens test for aldehydes
What is a meant by a monodentate bond?
The ligand bonds to the metal ion with only 1 co-ordinate bond
What is a chelate bond?
Bonds to the metal ion twice in 2 different locations, forming a ring
Why are chelate bonds preffered?
They are very stable as they often replace multiple monodentate ligands, a reaction which has an increase in entropy.
What is meant by bidentate?
Attached to the metal ion with 2 dative bonds per ligand
What is meant by multidentate?
Attach to the central metal ion with 3 or more dative bonds
What is EDTA?
Ethyldiammineteraacetic acid is a hexadentate ligand
- it can trap ions and in doing so reduces their reactivity
- it reduce metal ion impurities and chelation therapy can remove mercury and lead when somebody is poisoned
What is a ligand exchange reaction?
When one or more ligands are taken from a complex and replaced
What causes the characteristic colour of copper?
The characteristic blue colour (sulphate and chloride) is due to the presence of hexaaquacopper (II) ion
What colour is anhydrous copper?
Anhydrous salts contain no water molecules, white anhydrous copper sulphate is added turns blue
What happens when you add dilute ammonia to copper?
- ammonia solution acts as a base
blue solution to pale blue precipitate
What happens when you add ammonia to copper in excess?
Pale blue precipitate - deep blue solution
What happens when you add HCl to copper?
Initiates the ligand exchange
Blue solution to a green solution
What happens when you add sodium hydroxide to cobalt?
Pink solution to a blue precipitate
What happens when you add ammonia to cobalt?
Pink solution to green precipitate
What happens when you add excess ammonia to cobalt?
Green precipitate to brown solution
What happens when you add HCl to cobalt?
Pink solution to a blue solution
What will occur in transition redox reactions?
A change in colour
What can fe2+ be oxidised with?
H+/MnO4-
Purple to pink
What can fe2+ be reduced with?
I-
Turns dark blue (stronger with starch)
What can Cr3+ be oxidised with?
h2o2 (OH-)
green to yellow
What can Cr2O7 2+ be reduced with?
Zn/H+
orange to green
What is Cu2+ reduced with?
I-
white to brown
How can Cu2+ disproportionate?
Turns into cu2+ and cu
pink/brown solid to light blue
Why are transition metal complexes different colours?
The origin of colour in transition metal complexes results from the absorption of light energy as the electrons moves between 2 non-degenerate orbitals
What is octahedral splitting?
The energy levels of the d-orbitals are raised so they are no longer degenerate
- they are not raised by the same amount
What is tetrahedral spliiting?
When 4 anions approach the ions and form a tetrahedral complex, more complex repulsions cause splitting of the orbitals into 2 distinct levels
What does the energy gap between the high energy and low energy non-degenerate orbitals depend on?
- the metal ion
- the metals oxidation state
- the type of ligands surrounding the metal ion
- the arrangement of ligands surrounding the metal ion
- the number of ligand changes the coordination number but you will also be changing the ligands
What is catalysis?
The increase in rate of reaction caused by the addition of a catalyst
What is a homogeneous catalyst?
In the same phase as the reactant
What is a heterogeneous catalyst?
Different phase as the reactant (eg the haber process)
