McMurry (kap.1,11) - Describing chemical bonds: MO Flashcards
Two models are used to describe covalent bonds, which ones?
Valence bond theory
Molecular orbital theory
What is the valence bond approach?
Imagine two people shaking hands.
In VBT, a bond forms when two atoms “shake hands,” meaning their orbitals (regions where electrons are likely to be) overlap.
The bond is like a handshake between specific parts of the atoms (atomic orbitals) and is localized, meaning it stays between the two people (atoms).
Uses hybrid atomic orbitals to account for geometry and assumes the overlap of atomic orbitals to account for electron sharing.
What is the molecular orbital approach to bonding?
Imagine a group of people pooling their resources.
In MOT, all the atomic orbitals of the atoms in a molecule combine to form “shared” molecular orbitals.
These molecular orbitals belong to the whole molecule, not just a single pair of atoms. Electrons are like pooled money that anyone in the group can use. Some molecular orbitals are bonding (help hold the atoms together), and some are antibonding (can weaken the bond if they are filled).
Describes the covalent bond formation as arising from a mathematical combination of atomic orbitals (wave functions) on different atoms to form molecular orbitals - belong to the entire molecule rather than one atom.
what is an atomic orbital? whether unhybridized or not?
and what does a molecular orbital describe?
The region of space around an atom where an electron is likely to be found.
A molecular orbital describes a region of space in a molecule where an electron is likely to be found.
an atomic orbital has a specific shape, size and energy, is the same applied for a molecular orbital?
Yes
2 orbital combinations can occur in 2 ways, one can be additive and one can be substractive.
The additive combination leads to the formation of a molecular orbital that is lower in energy and egg shaped.
The subtractive combination leads to the formation of a molecular orbital that is higher in energy and has a node between nuclei (If there is a node between nuclei, it means there is a region of zero electron density (probability of finding an electron) between the two atomic nuclei.).
Has the shape of an elongated dumbbell.
How is the energy level of the additive combination?
It is lower in energy than two hydrogens 1s atomic orbital and is called bonding MO.
How is the energy level of the subtractive combination?
Higher in energy than the two hydrogen 1s atomic orbitals and is called antibonding MO.
Too read about the MO of pi orbital (see page 21)
see page 21
