Unit 8: Advanced Theories of Covalent Bonding
Orbitals actually merging into hybrids, and a molecular orbital diagram that gets oxygen's magnetism right where Lewis structures fail.
7 topics · 27 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
8.1 Valence Bond Theory and Orbital Overlap
- How it worksHow does valence bond theory picture a covalent bond as two atomic orbitals merging into one shared region?
- Common mistakeWhy isn't a sigma bond just any bond that happens to lie along the axis connecting two nuclei?
- Going furtherWhat happens to bond strength as two overlapping orbitals are pulled farther and farther apart?
Your turn1 of 2
A sigma bond is often described as lying directly along the axis connecting two bonded nuclei. Why isn't a sigma bond simply defined as any bond that happens to lie along that axis?8.2 sp3 Hybridization
- Common mistakeWhy isn't hybridization something that happens to an atom whether or not it's actually about to bond?
- How it worksHow do one s orbital and three p orbitals mix together to create four equivalent sp3 hybrid orbitals?
- Worked exampleFind the hybridization of the central carbon atom in methane, CH4, from its electron domain geometry.
- Going furtherWhat happens to nitrogen's hybridization in ammonia compared to carbon's in methane, given that nitrogen carries a lone pair?
Your turn1 of 2
Hybridization mixes 1 s orbital with 2 p orbitals on the same atom. How many equivalent hybrid orbitals does this produce in total?8.2 sp2 Hybridization and π Bonds
- How it worksHow does mixing one s orbital with two p orbitals leave one unhybridized p orbital free to form a π bond?
- How it worksWalk me through how sideways overlap of two unhybridized p orbitals creates the π bond in ethylene, C2H4.
- Worked exampleFind the hybridization of each carbon atom in ethylene, C2H4.
- Common mistakeWhy isn't a double bond just two identical sigma bonds stacked directly on top of each other?
Your turn1 of 2
A carbon-carbon double bond is drawn as two parallel lines. Why isn't a double bond actually two identical sigma bonds stacked directly on top of each other?8.3 sp Hybridization and Triple Bonds
- How it worksHow does sp hybridization leave two unhybridized p orbitals free to form the two separate π bonds in a triple bond?
- Worked exampleFind the hybridization of each carbon atom in acetylene, C2H2, and count its sigma and π bonds.
- Common mistakeWhy doesn't a triple bond simply have three times the bond strength of a single bond?
Your turn1 of 2
A carbon-carbon triple bond is stronger than a double bond, but not simply three times as strong as a single bond. Why doesn't a triple bond have exactly three times the strength of a single bond?8.2 Hybridization for Expanded Octets: sp3d and sp3d2
- How it worksHow do d orbitals combine with s and p orbitals to build the sp3d and sp3d2 hybrids needed for five or six electron domains?
- Worked exampleFind the hybridization of the central atom in sulfur hexafluoride, SF6.
- Common mistakeWhy isn't expanded-octet hybridization available to elements sitting in the second row of the periodic table?
- Ties togetherHow does the hybridization needed for an expanded octet connect back to why period 3 elements can break the octet rule at all?
Your turn1 of 2
Sulfur (period 3) can form SF6 using sp3d2 hybridization, but nitrogen (period 2) can never form an analogous NF6-type expanded-octet compound. Why isn't expanded-octet hybridization available to period 2 elements?8.4 Molecular Orbital Theory: Bonding and Antibonding Orbitals
- How it worksHow do two atomic orbitals combine mathematically into one bonding molecular orbital and one antibonding molecular orbital?
- How it worksWalk me through filling the molecular orbital diagram of H2 and reading off its bond order.
- Common mistakeWhy isn't an electron sitting in an antibonding orbital simply doing nothing to the bond?
- Going furtherWhat happens to the bond order, and to whether the molecule even exists, when you fill the same diagram for He2?
Your turn1 of 2
A diatomic molecule has 6 electrons filling its bonding molecular orbitals and 4 electrons filling its antibonding molecular orbitals. Find its bond order.8.4 Molecular Orbital Diagrams for Period 2 Diatomics
- How it worksHow does mixing of the 2s and 2p orbitals flip the energy order of the sigma and π molecular orbitals for elements lighter than oxygen?
- Worked exampleFind the bond order and magnetic behavior of O2 by filling in its full molecular orbital diagram.
- Worked exampleFind the bond order of N2 from its molecular orbital diagram and compare it with O2's bond order.
- Common mistakeWhy can't a Lewis structure alone predict that O2 is paramagnetic?
- Ties togetherHow does molecular orbital theory's correct prediction for O2 show where valence bond theory and Lewis structures both fall short?
Your turn1 of 2
A period 2 diatomic molecule has 8 valence electrons filling bonding molecular orbitals and 4 valence electrons filling antibonding molecular orbitals. Find its bond order.