Chapter 7: Theories of Chemical Bonding Flashcards
Localized bonding
Electrons are localized in the bonds between two atoms, usually in pairs
Delocalized bonding
Bonds delocalized over several atoms, which explains some chemical properties
Orbital overlap
A combination of wave orbitals, generating a new orbital with high electron density between the nuclei
What type of overlap do diatomic molecules have? HF
1s-2p overlap
What type of overlap do diatomic molecules have? F2
2p-2p overlap
What is the overlap in H2S?
1s-3p overlap
Atomic orbitals can be hybridized to generate______. These mixed orbitals match the __________. All electrons around _________ must be in orbitals.
A new set of directional orbitals
Orbital geometry of the compounds
The central atom
Hybridization
Combining atomic orbitals on a particular atom to form a special set of directional orbitals
sp3 hybrid orbitals = ________ molecular geometry
Tetrahedral
The ______ of an inner atom determines the number and type of hybrid orbitals
Steric number
Do hybrid orbitals form localized or delocalized bonds with atomic orbitals/other hybrid orbitals?
Localized
Are outer atoms hybridized?
No
sp2 hybrid orbitals = _______ geometry
Trigonal planar (steric number 3)
sp hybrid orbitals = ________ geometry
Linear (steric number 2)
sp3d hybrid orbitals = _______ geometry
Trigonal bipyramidal (steric number 5)
sp3d2 hybrid orbitals = __________ geometry
Octahedral (steric number 6)
Double bond
Has two sets of bonding electrons and requires two sets of overlapping orbitals
Triple bond
Has three sets of bonding electrons and requires three sets of overlapping orbitals
A single overlap of two orbitals is called______? Where is the electron density distribution?
A sigma bond (electron density is distributed along the axis)
A double overlap of two orbitals is called________? Where is the electron density distributed?
A pi bond (electrons density is distributed above and below the bond axis)
Why does silicon form weak pi bonds?
The 3p orbitals are too far apart for strong side-by-side overlap
What type of bonds are triple bonds?
One sigma bond and 2 pi bonds
How can bonding in diatomic molecules second row elements be explained?
- Localized bonding
- Pure s and p atomic orbitals that combine to produce orbitals that are delocalized over several atoms leading to molecular orbitals
What are the advantages of molecular orbitals over localized bonding theory?
- You can predict bond lengths and energies
- Predict magnetic properties
- Correctly explain structures of molecules that do not follow lewis dot structure
What is the first principle of MO theory?
The total number of molecular orbitals produced by a set of interacting atomic orbitals is always equal to the number of interacting atomic orbitals
What does adding orbitals =?
Bonding molecular orbitals
What does subtracting orbitals =?
Anti-bonding molecular orbitals
What is the second principle of MO theory?
The bonding molecular orbital is lower in energy than the parent orbitals and the anti-bonding orbital is higher in energy
The system is _______when electrons are assigned to the bonding orbitals
Stabilized
The system is ________when electrons are assigned to the anti-bonding orbitals because the energy of the system is higher
Destabilized
How do you calculate bond order?
1/2 (#electrons in bonding MOs-#electrons in anti-bonding MOs)
What is the third principle of MO theory?
Electrons of the molecule are assigned to orbitals based on the aufbau principle and Hund’s rule
A bond order of 1 represents____?
A single bond
What does a bond order of 1.5 indicate?
A bond that is intermediate between a single and double bond
What is the 4th principle of MO theory?
Atomic orbitals combine to form molecular orbitals most effectively when the atomic orbitals are of similar energy (ex. 1s and 1s)
Removing an electron (neutral to cation) has what effect?
Increases bond energy and decreases bond length
What is orbital mixing?
The overlap of 2s and 2pz orbitals stabilizes sigma s and destabilizes sigma p.
What is a conjugated pi system?
Molecules that have alternating single and double bonds
What are three-centre pi orbitals?
A chemical bond where three atoms share electrons, while a pi bond is a covalent bond where two lobes of orbitals on different atoms overlap laterally
Where does stability come from in bonding molecules?
The delocalized pi system
Delocalized pi systems result in?
Increased stability and often in coloured compounds
Are benzene rings unstable?
No. They are very stable due to its 6 pi electrons
The energy spacing between orbitals _________ as the number of _________ increases.
Decreases
Delocalized orbitals
Band gap (Eg)
The energy difference between the filled bonding orbitals and the empty anti-bonding orbitals
Semiconductors can become detectors in the presence of?
An appropriate energy source
