KA 3: transition metals Flashcards
What are d-block transition metals?
Metals with an incomplete d subshell in at least one of their ions
what does the filling of d-orbitals follow?
what are the exceptions?
the aufbau principle
chromium and copper atoms
what are these exceptions due to?
the special stability associated with the d subshell being half-filled or completely filled
what happens when atoms from the first row of the transition elements form ions?
it is the 4s electrons that are lost first rather than the 3d electrons
what can be used to determine whether oxidation or reduction has occurred?
changes in oxidation number of transition metal ions
what can oxidation be defined as?
an increase in oxidation number
What can reduction be defined as?
decrease in oxidation number
what are compounds containing metal in high oxidation states usually classed as?
oxidising agents
what are compounds containing metal in ow oxidation states usually classed as?
reducing agents
an element is said to be in a particular oxidation state when…
…it has a specific oxidation number
how can the oxidation number be determined?
-uncombined elements have an oxidation number of 0
-ions containing single atoms have an oxidation number that is the same as the charge on the ion
-in most of its compounds, oxygen has an oxidation number of −2
-in most of its compounds, hydrogen has an oxidation number of +1
-the sum of all the oxidation numbers of all the atoms in a neutral compound must add up to zero
-the sum of all the oxidation numbers of all the atoms in a polyatomic ion must be equal to the charge on the ion
what can a transition metal have in its compounds?
different oxidation states
Compounds of the same transition metal in different oxidation states may have…
different colours
ligands may be…
negative ions or molecules with non-bonding pairs of electrons that they donate to the central metal atom ion, forming dative covalent bonds.
What can ligands be classified as?
Monodentate, bidentate up to hexadentate
what happens in the formation of a simple covalent bond?
each atom supplies one electron to the bond
What is a dative covalent bond?
a covalent bond (a shared pair of electrons) in which both electrons come from the same atom
how is a dative bond shown?
using an arrow
what is it possible to do?
to deduce the ligand classification from a formula or structure of the ligand or complex
What is the coordination number?
The total number of bonds from the ligands to the central transition metal
what is a complex?
a transition metal surrounded by ligands
How can names and formulae be written?
-ligands are listed first followed by the metal
-if there is more than one type of ligand use the usual prefixes of di,tri etc
-when listing ligands, do so alphabetically (the prefixes don’t count)
what do the IUPAC rules cover?
-central metals that obey the rules
-copper (cuprate) and iron (ferrate)
-ligands, including water, ammonia, halogens, cyanide, hydroxide and oxalate
-roman numerals are shown for the oxidation state of the metal
how do you make the formula?
-the complex is enclosed within square brackets
-the metal symbol is written first then the ligands in alphabetical order
-the atom bound to the transition metal should always be listed first where reasonable to do so
-the charge on the complex goes outside the brackets
what happens if a complex is overall negative?
the metal name ends in “-ate”
what happens to the name if the complex has a positive or neutral charge?
the name doesn’t change
what happens to the d-orbitals in a complex of transition metals?
they’re no longer degenerate
what is the splitting of the d-orbitals into higher and lower energies due to?
repulsion between the electrons in the approaching ligand and electrons in orbitals lying along the axes.
what does the extent of the splitting depend on?
the ligands involed
what are strong field ligands?
Ligands that cause a large difference in energy between subsets of d orbitals
what are weak field ligands?
ligands that cause a small energy difference between subsets of d orbitals
what is the spectrochemical series?
where ligands are placed in an order of their ability to split d orbitals
the greater the splitting the greater…
…the energy difference between the two subsets of orbitals
when is light absorbed?
and what does this account for?
When electrons in a lower energy d orbital are promoted to a d orbital of higher energy
the colour of many transition metal complexes
if light of one colour (from the visible spec) is absorbed, what happens?
the complementary colour will be observed
what can transition metals and their compounds act as?
catalysts
what state are heterogeneous catalysts in?
a different state to the reactants
what can heterogeneous catalysts be explained in terms of?
-formation of activated complexes
-the adsorption of reactive molecules onto active sites
what is thought to allow activated complexes to form?
what does this provide?
The presence of unpaired d electrons or unfilled d orbitals
reaction pathways with lower activation energies compared to the uncatalysed reaction
where does the reaction occur?
on the surface of the catalyst
what happens when the reaction occurs om the surface of the catalyst?
- partially filled d-orbitals can form weak temporary bonds
- this allows new bonds to form between atoms on the surface
- the products move away (lower activation energy pathway) and the active site on the metal can be reused
what state are homogeneous catalysts in?
the same state as the reactants
how can homogeneous catalysts be explained?
in terms of changing oxidation states with the formation of intermediate complexes.
give an example of the variability of oxidation states
(rochelle salts experiment)
