Molecular Orbitals and Bonding Concepts

Study Notes

Molecular Orbitals and Bonding

When two atomic orbitals combine, they can form either a bonding or an antibonding molecular orbital
A bonding orbital has lower energy than the atomic orbitals and is occupied by electrons that are shared between the two atoms, resulting in a bond
An antibonding orbital has higher energy than the atomic orbitals and is not occupied by electrons in a stable molecule, resulting in a reduction in bond strength

Molecular Stability

A molecule is stable if the number of bonding molecular orbitals (Nb) is greater than the number of antibonding molecular orbitals (Na)
This is because the bonding orbitals are lower in energy, and the electrons in them are more stable

Bond Order

Bond order is a measure of the strength and stability of a bond between two atoms
It is calculated as the difference between the number of electrons in bonding orbitals and the number of electrons in antibonding orbitals, divided by 2
Higher bond order indicates a stronger, shorter bond
A molecule with a bond order of zero does not exist (Na = Nb)

Homonuclear and Heteronuclear Diatomic Molecules

A homonuclear diatomic molecule contains atoms of the same element (ex: H2, O2, N2, Li2)
A heteronuclear diatomic molecule contains atoms of different elements (ex: CO, NO, HCl)

Intermolecular and Intramolecular Hydrogen Bonds

A hydrogen bond is a type of intermolecular force that occurs between a hydrogen atom bonded to a highly electronegative atom (like O, N, or F) and a lone pair of electrons on an adjacent atom
Intermolecular hydrogen bonds occur between molecules (ex: water molecules)
Intramolecular hydrogen bonds occur within the same molecule (ex: o-nitrophenol)

Properties of Hydrogen Bonding

Hydrogen bonding is a stronger type of intermolecular force compared to van der Waals forces
It affects the boiling point of liquids and the melting point of solids
The magnitude of hydrogen bonding is dependent on the strength of interaction between the hydrogen atom and the electronegative atom

Existence of Molecules

Not all combinations of atoms result in stable molecules
For example, He2 has a bond order of zero and therefore does not exist
H2, O2, and N2 all exist due to their stable bond orders

Nitrogen Molecule (N2)

The nitrogen molecule (N2) is diamagnetic
The bond order of N2 is 3.
N2 has a total of 14 electrons

Oxygen Molecules

The bond order of O2 is 2 and is a paramagnetic molecule.
O2- has a bond order of 1.5
O22+ has a bond order of 2.5
O22- has a bond order of 1
Shorter Bond Length corresponds to a higher bond order. Thus, O22+ (bond order 2.5) has the shortest bond length.

Molecular Shape

IF7 has a pentagonal bipyramidal structure, meaning it has 5 fluorine atoms arranged in a pentagonal plane, and 2 fluorine atoms at the apical positions above and below the plane
Square planar is not a possible structure for IF7 .

Description

This quiz explores the principles of molecular orbitals, including bonding and antibonding orbitals, stability of molecules, and bond order calculations. Test your understanding of how atomic orbitals combine to influence molecule formation and stability.