compounds and complexes Flashcards
atomic radius of group 6 elements (Cr, Mo, W and Sg)
increases Cr to Mo
W and Mo are the same due to lanthanoid contraction (poor shielding of 4f)
ionisation energy of g6
increases down due to increase in Zeff
subsequent removal of electrons from 2nd and 3rd row transition metals becomes easier due to shielding by inner electrons - gradual increase in 2nd and 3rd IE
end and 3rd row are more stable in high ox states and are easily oxidised
chemistry of chromium
group state 4s1 5d5 (stable half filled)
common ox states are 2,3 (most stable) and 6
oxoanions? for Cr?
negatively charged ions containing two or more elements (one is oxygen)
common for group 6
charged metal ions do not exist in isolation
oxoanion for Cr6+ is CrO42-
Cr0 and Cr2+
strong reducing agents that oxidise to Cr3+
Cr6+
is a strong oxidising agent in acids
as ox state increases…
tendency to remove electrons decreases - more electronegative, less metallic and more acidic (more able to accept an electron from a donor compound)
Cr2O3
amphiprotic (acid or base)
Coordination complex
a central atom bonded to molecules or anions (called ligands)
- cations are Lewis acids (electron pair acceptors)
- ligands are Lewis bases (electron pair donors)
- bonds are called coordinate bonds, donor covalent bonds or dative bonds
coordination compound
a salt (anion + cation) in which one or both ions is a coordination complex
- counter ions may be present to maintain charge or balance in the coordination compound
- compound may dissociate in solution and acts as an electrolyte
- ligands remain attached to the metal ion
kepert theory
complex shapes depend on repulsion of ligands
coordination number
the number of donor atoms around the metal
donor atom
atom that forms the coordination bond around the metal
linear
2 donors
trigonal planar
three donors
