ELE_IC Molecular Orbital Theory, MO of Diatomic and Polyatomic Molecules

linear combinations of atomic orbitals (LCAO)

Approximate solutions to these molecular Schrodinger equations can be constructed from _______, the sums and differences of the atomic wave functions.

amplitudes

Waves that describe atomic orbitals have both positive and negative phases or ________.

True.

As molecular orbitals are formed, the phases can interact constructively or destructively.

T or F?

Head-on overlap

This type of molecular orbital overlap produces a sigma orbital.

Side-on overlap

This type of molecular orbital overlap produces a pi orbital.

σ1s = bonding molecular orbital
σ1s* = antibonding molecular orbital

Two 1s orbitals that overlap produce two molecular orbitals designated as:

____ or bonding molecular orbital
____ or antibonding molecular orbital

σ1s = lies lower in energy
σ1s* = higher in energy

Energetically, the molecular orbitals split wherein:

____ lies lower in energy while the ____ is higher in energy.

molecular orbital energy level diagram

This diagram depicts the relative energies of molecular orbitals.

g for gerade

This label is used to describe orbitals symmetric to inversion.

u for ungerade

This label is used to describe orbitals antisymmetric to inversion.

bond order

The overall number of bonding and antibonding electrons determines the number of bonds or the ____________.

bond order = 1/2 (# of e- in bonding MOs - # of e- in antibonding MOs)

What is the formula for bond order?

True.

The larger the bond order, the more stable the molecule or ion is.

T or F?

same stability as separate atoms

If bond order = 0, what does this imply?

molecule is more stable than separate atoms

If bond order > 0, what does this imply?

True.

When 2 molecular orbitals of the same symmetry have similar energies, they interact to lower the energy of the lower orbital and raise the energy of the higher orbital.

T or F?

different energies

In heteronuclear diatomic molecules, the atomic orbitals have (similar, different) energies, and a given MO receives unequal contributions from these atomic orbitals.

more EN atom

The greater contribution to a bonding molecular orbital normally comes from the (more, less) electronegative atom.

The bonding electrons are then likely to be found close to that atom and hence be in an energetically favorable location.

Direct relationship

In polyatomic molecules, what is the relationship between the number of nodes in a MO, the antibonding character, and the orbital energy?

False. Lower in energy.

Orbitals constructed from lower energy atomic orbitals lie higher in energy.

T or F?

weakly bonding (lower the energy slightly)

Interactions between nonnearest-neighbour atoms are weakly (bonding, antibonding) if the orbital lobes on these atoms have the same sign; interferes constructively.

weakly antibonding

Interactions between nonnearest-neighbour atoms are weakly (bonding, antibonding) if the orbital lobes on these atoms have different signs; interfere destructively.