Flashcards in Transition metals Deck (101)
What are the rules for writing electronic configurations?
- Unless asked to, you don't need to give the full configuration; start with [Ar]
- 4s subshell comes before 3d
- Copper and chromium both only have 1 electron in their 4s subshells
- When forming ions, remove the 4s electrons first
*Why does 4s come before 3d?
The outer edges of the d subshell are further from the nucleus than the s subshell and therefore there is less attraction to the nucleus
*Why do copper and chromium only have 1 electron in their 4s subshells?
A full subshell or half filled subshell is particularly stable
What is the definition of a transition metal?
Transition metals are d-block elements that form one or more stable ions with incompletely filled d-orbitals
Why is zinc not classified as a transition metal?
It can only form a 2+ ion, which has a complete d subshell and so does not meet the criteria of having an incomplete d orbital in its ion
Why is scandium not classified as a transition metal?
It can only form a 3+ ion, which has an empty d orbital and so does not meet the criteria of having an incomplete d orbital in one of its ions
Why do many transition metals have variable stable oxidation states?
- They are able to donate and receive electrons and are able to oxidise and reduce because of the partially filled subshells of d electrons that can easily use and gain electrons
- The 4s orbital and 3d orbitals have very similar energies
- There isn't a huge jump in energy needed to remove the 3rd electron compared with the first and second
What is the pattern for successive ionisation energies for elements Sc-Zn?
Show a gradual increase in ionisation energy until all the 4s and 3d electrons have been removed. There is then a big jump as electrons start to be removed from inner core electrons
What is a complex ion?
A central metal ion surrounded by ligands
What is a ligand?
An atom or molecule that can donate a lone electron pair
What is coordinate bonding?
It is involved in complex formation and is when the shared pair of electrons in the covalent bond come from only one of the bonding atoms
What is coordination number?
The number of coordinate bonds formed to a central metal ion
What are the 3 types of ligands?
Monodentate, bidentate and multidentate
What is a monodentate ligand and what are some examples?
One that can form one coordinate bond per ligand
e.g. H2O, NH3, Cl^-
What is a bidentate ligand and what are some examples?
One that forms 2 coordinate bonds per ligand as it has 2 atoms with lone pairs
e.g. NH2CH2CH2NH2, C2O4^2-
What is a multidentate ligand and what are some examples?
One that forms 3 or more coordinate bonds per ligand
e.g. edta which forms 6 coordinate bonds per ligand
What changes can give rise to coloured transition metal ions?
- Oxidation state
- Coordination number
Why do transition metal ions give rise to coloured compounds?
Complex ions cause light to be absorbed because ligands split their d orbitals into 2 different energy levels
An electron can then be promoted from the lower energy level by absorbing a particular wavelength of light. The remaining wavelengths are then transmitted and that results in the colour of the complex. The wavelength absorbed depends on the size of the energy gap.
Complex ions can also have different shaps (e.g. octahedral and tetrahedral) and these split the d orbital differently, which can lead to different colours being seen
Why do differently-shaped complex ions affect the colour of a transition metal compound?
The ligands repel different d-orbitals which means there is a different energy requirement from the different amounts of repulsion, meaning different wavelengths are absorbed and therefore different colours are seen
How can the colour be changed?
Changing a ligand or the coordination number will alter the energy split between the d orbitals, changing ΔE, hence changing the frequency of light absorbed
Why are scandium ions uncoloured?
The Sc^3+ ion has no d electrons left to move around, so there cannot be an energy transfer equal to that of visible light as no energy will be absorbed to promote electrons
Why are Zn^2+ and Cu^+ ions uncoloured?
Both have 3d10, so there is no space for electrons to transfer, so no energy transfer equal to that of visible light is possible
What feature allows a substance to be a ligand?
A lone pair of electrons
Why do chloride ions form tetrahedral complexes when water and ammonia form octahedral complexes?
Chloride ions are bigger and negatively charged, so not as many can fit around the central ion and they repel each other to a greater degree
Why do most metal ions not form square planar complexes?
It is usually a less favourable shape for complexes as repulsion is not minimised
Why is cis-platin supplied as a single isomer for cancer treatment?
It works as 2 chloride ions are displaced, as it undergoes ligand exchange, and the molecule joins on to the same strand of DNA, stopping the replication of cancer cells. Both chlorides have to be on the same side for this to happen, so cis-platin is the only isomer for which this happens, and trans-platin is harmful
Why do chloride ions only work as monodentate ligands, despite having 4 lone pairs?
Lone pairs have to be far enough apart for dative covalent bonds to form from the metal ion
Why is CO toxic to humans?
Oxygen binds to the haem which is an iron (II) complex, but CO can replace oxygen as a ligand, and this coordinate bond is stronger so it binds irreversibly and prevents the oxygen bonding to it, reducing the blood's capacity to carry oxygen
Zn will reduce V from 5^+ to 2^+ in several stages. What are the colour changes and the standard electrode potentials?
VO2+ (+5) -> VO^2+ (+4)
Yellow -> blue (+1.76V)
VO^2+ (+4) -> V^3+
Blue -> green (+1.1V)
V^3+ -> V^2+
Green to lilac (+0.50V)
V^2+ -> V
Electrode potential is -0.37V