Lecture Fifteen - Transition metal characteristics Flashcards
Describe the relationship between colour and transition metals.
May transition metal compounds are coloured.
Electrons in partially filled d-orbitals can absorb visible light and move to d-orbitals with slightly higher energy.
Describe the relationship between transition metals and magnetism.
Many transition metal compounds are paramagnetic.
Paramagnetism is where there is an unpaired electron, that is, at lease one orbital is half filled (unpaired spins). In transition metals, they are paramagnetic when there is a d-subshell that is partially filled. Magnetic field is randomly arranged unless placed in an external magnetic field - ferromagnetic.
Diamagnetic is where all electron spins are paired, no net magnetic moment.
Main group ionic compounds are colourless and diamagnetic.
Electrons are paired. energy of visible light is not enough to promote electrons into empty higher orbital levels.
Describe some characteristics of group six elements, particularly chromium.
No obvious increase in reactivity as we descend the group.
Ionisation energy increases as we descend transition metal groups.
Metals become less reactive and poorer reducing agents as we move down the group.
Chromium:
Ground state configuration is 4s1 3d5.
Common oxidation states are +2, +3 and +6.
Stainless steel contains up to 18% Cr, which slows oxidation.
Cr metal and Cr 2+ are strong reducing agents.
In acid, Cr(VI) oxo-anions are strong oxidising agents.
As a general rule:
High oxidation state = good oxidising agent.
Low oxidation state = good reducing agent.
Non-metallic character and acidity increase with oxidation state.
CrO is basic and ionic - dissolves in acid -> Cr2+.
Cr2O3 is amphiprotic (can be oxidised and reduced).
CrO3 is deep red, covalent and acidic.
