Chemistry Multiple Choice Questions on “Bonding in Metal Carbonyls”.
1. What is the geometry of pentacarbonyliron(0)?
a) Square planar
b) Tetrahedral
c) Trigonal bipyramidal
d) Octahedral
Answer: c
Clarification: The coordination number of pentacarbonyliron(0) is 5 as CO is a unidentate ligand and hence its geometry id trigonal bipyramidal.
2. The following structure of a carbonyl compound is formed by which transition metal.
a) Ni
b) Cr
c) Mn
d) Co
Answer: d
Clarification: There are 8 carbonyl ligands present. This compound is formed by cobalt metal ion an is named octacarbonyldicobalt(0). It also has Co-Co bond bridged by two carbonyl groups.
3. The metal-carbon bond in metal carbonyls possesses only sigma character.
a) True
b) False
Answer: b
Clarification: The M-C bond in metal carbonyls has both sigma and pi bonds and this helps in creating a synergic effect and, hence strengthening the bond.
4. How is the M-C pi bond formed?
a) Donation of electron pair of half-filled metal d orbital to empty bonding pi orbital of CO
b) Donation of electron pair of filled metal d orbital to empty bonding pi orbital of CO
c) Donation of electron pair of filled metal d orbital to empty antibonding pi orbital of CO
d) Donation of electron pair of half-filled metal d orbital to empty antibonding pi orbital of CO
Answer: c
Clarification: The pi bond involves donation of electrons from filled metal d orbitals into empty antibonding pi orbitals of CO. This is also called a back bond.
5. The donation of lone pair of electrons of CO carbon into the vacant orbital of metal atom results in _________ bond.
a) sigma
b) pi
c) back
d) synergic
Answer: a
Clarification: Synergic bonding is the overall effect of the sigma and pi interactions in metal carbonyl bonds. M-C pi bonds are also known as back bonding.