Topic C.2: Transition elements Flashcards
(13 cards)
Definition of transition elements
An element that forms at least one stable ion with a partially filled d sub-level
What are the properties of transition elements
Variable oxidation states
High melting and boiling points
Large density
Magnetic properties
Behave as catalysts
Form coloured compounds
Form complex ions with ligands
Why do transition metals have high melting and boiling points
They have strong metallic bonding due to the availability of both 3d and 4s electrons for delocalisation
The small metallic radius also causes a strong electrostatic attraction of the protons in the nucleus for the delocalised electrons
Why do transition metals have high densities
Transition metals have a small metallic radius and a ‘closely packed’ structure
Why is the decrease in metallic radii small in transition metals compared to the decrease across elements in period 2 and 3.
Across the period, nuclear charge increases but each ‘additional’ electron enters the inner 3d sub-level
The inner 3d sub-level electrons provide a more effective shield between the nucleus and outer 4s electrons, thus ‘nullifying the influence of an added proton in the nucleus
Where are electrons removed from in transition metal ions
Electrons are removed from the 4s sub-level first, followed by the 3d sub-level
Why do most transition elements exhibit a variety of oxidation states
The 4s and 3d sub-levels are close in energy and there are no ‘big jumps’ in the successive ionisation energies when the 4s and 3d electrons are removed
What is a d-block metal complex ion
It consists of a central metal ion closely bonded by coordinate covalent bonds to a cluster of molecules or negative ions called ligands
What are ligands
Negative ions or molecules with at least one lone pair of electrons, used to form a coordinate covalent bond with the central metal ion
What is coordination number
Number of coordinate bonds formed between the ligands and transition metal ion
Why can transition metal ions form complexes
They have a relatively high charge density of the cation, allowing it to attract the lone pair of electrons from ligands
They have energetically accessible empty orbitals (3d, 4s or 4p) to accept the lone pair of electrons from ligands
What factors influence the colour of complexes
Metal ion
Number of d electrons
Nature of the ligand
Geometry of the complex
How does the metal ion affect the colour of the complex
If the nuclear charge of the metal ion is higher, the strength of the coordination bond is greater, so the energy gap will be higher. Thus the wavelength of light absorbed is lower, and the colour of observed light has a higher wavelength
