1c- Transition metals Flashcards
What is a transition metal?
metals with an incomplete d subshell in at least one of their ions
The filling of d orbitals follows the aufbau principle with the exception of which two atoms?
Chromium and copper
Why do the d orbitals in chromium and copper atoms not fill up following the aufbau principle?
Due to special stability associated with the d subshell being half-filled or completely filled
When atoms from the first row of transition metals form ions, which electrons are lost?
4s electrons are lost first rather than the 3d electrons
What do oxidation and reduction reactions involve?
The transfer of electrons
How are oxidation numbers always written?
Sign first then number, e.g. +2 or -3
What oxidation number do uncombined elements have?
Zero
What is the oxidation number of an ion containing single atoms?
The oxidation number is the same as the charge on the ion
In most of its compounds what is the oxidation number of oxygen?
-2
In most of its compounds what is the oxidation number of hydrogen?
+1
What must the sum of all the oxidation numbers of all the atoms in a neutral compound add up to?
Zero
What must the sum of all the oxidation numbers of all the atoms in a polyatomic ion be equal to?
The charge on the ion
Compounds of the same transition metal can have different colours, why is this?
Different oxidation states of the transition metal (a change in oxidation number usually means a change of colour)
What can oxidation be defined as?
An increase in oxidation number
What can reduction be defined as?
A decrease in oxidation number
What can changes in oxidation number be used to determine?
Whether oxidation or reduction has occured
Compounds containing metals in high oxidation states are often what?
Oxidising agents
Compounds containing metals in low oxidation states are often what?
Reducing agents
What is a ligand?
A molecule, ion or atom which contains at least one non-bonded pair of electrons
What can a ligand do?
Donate their lone pair of electrons to the central metal atom or ion, forming a dative covalent bond (coordinate bond)
How can ligands be classified and what do these classifications mean?
- monodentate (1-toothed) = can form one coordinate bond
- bidentate (2-toothed) = can form two coordinate bonds
- hexadentate (6-toothed) = can form six coordinate bonds
What is the coordination number and what does it determine?
The total number of bonds from the ligands to the metal center, this determines shape
What are the four rules when naming metal complexes?
- number and name of ligands is given first
- name of metal then oxidation number in brackets (roman numeral)
- if complex is positive or neutral, name of metal doesn’t change
- if complex is negative, ending changes to -ate
How do ligands always appear?
In square brackets
In a complex of a transition metal the d orbitals are no longer what?
Degenerate
When does the splitting of d orbitals to higher and lower energies occur?
When the electrons present in approaching ligands cause the electrons in the orbitals lying along the axes to be repelled
Ligands which cause a large difference in energy between subsets of d orbitals are known as what?
Strong field ligands
Ligands which cause a small energy difference between subsets of d orbitals are known as what?
Weak field ligands
Ligands can be placed in an order of their ability to split d orbitals. What is this called?
The spectrochemical series
How can the colours of many transition metal complexes be explained?
In terms of d-d transitions
What happens when electrons in a lower energy d orbital are promoted to a d orbital of higher energy?
Light is absorbed
If light of one colour is absorbed, what colour will be observed?
The complementary colour
When do electrons transition to higher energy levels?
When energy corresponding to the ultraviolet or visible regions of the electromagnetic spectrum is absorbed
What can transition metals and their compounds act as?
Catalysts
How can heterogeneous catalysts be described?
They are in a different state to the reactants
What can heterogeneous catalysts be explained in terms of?
The formation of activated complexes and the adsorption of reactive molecules onto active sites
How can homogeneous catalysts be described?
They are in the same state as the reactants
What can homogeneous catalysts be explained in terms of?
Changing oxidation states with the formation of intermediate complexes
