11/27 Chem 1A Lecture 21: (Molecular Orbital Theory, Bond Energy & Mixing Orbitals)

Orbitals

*Mixing* means the sigma and the pi o__________ switch places in molecular orbital theory.

Sigma star

A σ* bond is also referred to as a s________ s_______ bond.

Lone pairs

According to valence bond theory, l_____ p______ are always a result of filled *sp hybrid orbitals.* :N≡N:

Atomic orbital

An a________ o_________ is a three-dimensional region around the nucleus of an atom that describes an electron's probable location. Can be ranked in terms of higher or lower energy. Electrons like to populate the lower energy ones first.

Bond order

B_______ o________ refers to the number of shared electron pairs between two atoms 1/2 times (number bonded electrons - number of unbonded electrons)

Bond energy

B________ e__________ is a measure of how many kilocalories are needed to break a *covalent* bond.

Bonding, antibonding

Bond energy is measured as a ΔH/kilocalorie value. It is the difference in energy between b__________ and a_______________ orbitals.

Lower

Constructive interference does not occur in the antibonding molecular orbitals, but rather the bonding ones. The *bonding molecular orbitals* are always [lower or higher] in energy levels?

Destructive

D________________ interference is the interference that occurs when two waves combine to make a wave with a smaller amplitude. When electrons move in this fashion, no bond can form. Waves amplitudes differ!

Antibonding

Destructive interference (incompatible electron wavelengths) occurs in the [bonding or antibonding] molecular orbitals?

Atomic

How many *molecular orbitals* you make depends on how many a_________ orbitals you are combining.

Same

In a molecular orbital structure, constructive interference always occurs between atomic orbitals bonding due to [same or opposite] charges?

Lone pairs

L______ p_______ are sets of 2 valence electrons that are not involved in covalent bond formation. They are localized on a single atom.

Pi

Mixing cannot change the [sigma or pi] overlap in MO theory?

Close

Mixing occurs when sigma and pi orbitals are [close or far] away in energy-levels from one another?

Top

Mixing only affects the [top or bottom?] of the molecular orbitals?

Stable

Molecular orbitals that are lower in energy are considered more s_______.

Overlap

O_________ of orbitals is not the sole arbiter of determining energy levels. So, MO theory describes bonding using energy values in sigma and pi terms, and then we can determine which is stronger.

250

One of the three rules of creating a molecule, according to molecular orbital theory: Energy levels of orbitals bonding with each other MUST be in a range of no more than _ _ _ kilocalories within each other.

Overlap

One of the three rules to creating a molecule is that the type of o_________ between atomic orbitals is important. Is it a sigma-type or pi-type?

Lower

The [lower or higher] energy orbitals are more ready to react?

Antibond

The a___________ molecular orbital always breaks bonds that are made (such as existing sigma bonds or existing pi bonds). These result in 2 lone pairs, one from the σ orbital and one from the σ* orbital.

Lattice energy

The equivalent of "bond energy" (a covalent compound thing) in ionic compounds is referred to as l________ e________.

Lower

The orbitals whose bonds will be broken first in MO theory are [lower or higher?] energy orbitals.

3

There are _ (how many rules?) to the *molecular orbital theory*/MOT?

Same

There is a [same or unequal] difference in *energy* that antibonding molecular orbitals rise above their original atomic orbital energy levels compared to the decrease in energy levels of bonding orbitals.

50

There is a _ _% chance of a molecular orbital actually forming a bond.

Spatial

There is a s________ rule to creating a molecule by overlapping orbitals together. A physical overlap must be possible. Can only happen when orbitals are the same shape! S with S only, no S with P.

Unfilled

Triple bonds can occur when "star" (antibonding) orbitals are [filled or unfilled?] This is because this causes the breaking of bonds.

False

True or false: Hybridization occurs in the molecular orbital theory as it does in valence bond theory.

True

True or false: If molecular orbitals are close enough to each other in energy, they can actually overlap and change energy levels. This is called "mixing." If mixing occurs, this usually causes the pi bond to be as strong or stronger.

True

True or false: Mixing can cause bond energies to change between the newly-rearranged orbitals. (Molecular orbital theory)

True

True or false: Most likely, the 2S subshell split up into a σ and a σ* will result in lone pairs for some elements because they both tend to be occupied by electrons. This helps us avoid hybridization, since it means it's OK for an atom with a full 2S to still bond with another atom.

True

True or false: Orbital change energy levels in molecular orbital theory.

True

True or false: Sigma orbitals always have a higher bond energy than pi orbitals.

False

True or false: To cancel out two pi bonds, the antibonding pi orbitals both can be just half-filled with electrons (1 electron each).

True

True or false: Valence bond theory has no "bonds" or "antibonds."

False

True or false: You can have a sigma star orbital without having a sigma orbital in "molecular orbital theory."

Lower

What types of molecular orbitals will electrons fill up first? Molecular orbitals with [lower or higher] energy levels?

Sigma, sigma star

When combining with any 2p or other p orbitals, you will have the option of creating a molecular orbital that is a s______ and one that is a s______ s______.

No mixing

When is the sigma bond guaranteed to be strongest in MO theory? [Mixing or no mixing?]

Mixing, under

When the 2S and 2P orbitals overlap, they switch off energy levels. This is called m__________. Does not always happen. Only when energy difference between orbitals is [under or over?] 250 kilocalorie difference between the *2S* and the *2P*.

Sigma

Which type of bond overlaps MORE area? [Sigma or pi?] Usually indicates a greater or stronger bond, but NOT the only qualification for determining bond strength.

Constructive interference

[Constructive interference or destructive interference?] is the interference that occurs when two waves combine to make a wave with a larger amplitude. Bonds form from this type of interference, when atomic orbitals overlap and reinforce each other. "Overlapping waves." Happens when both waves are the same. Ex: Both waves are positive.