chem 2- molecular orbital theory (*exam 1)

advanced theories of covalent bonding

what is paramagnetism

phenomenon in which a material is not magnetic itself but is attracted to a magnetic field

occurs when unpaired electrons are present

what is diamagnetism

phenomenon where a material is not magnetic but is repelled by a magnetic field

what does molecular orbital theory provide to us

an explanation of chemical bonding that accounts for the paramagnetism of the oxygen molecule

a model for describing the energies of electrons in a molecule and the probable location of these electrons

why is molecular orbital theory different from valence bond theory

valence bond theory used hybrid orbitals that are assigned to one specific atom

molecular orbital theory uses the combination of atomic orbitals to yield molecular orbitals that are delocalized over the entire molecule

how is the behavior of an electron described

a wave function, analogous to the behavior in an atom

what is a molecular orbital (wave function²)?

the region of space in which a valence electron in a molecule is likely to be found.

when is a molecular orbital full

when it contains two electrons with opposite spin (same as an atomic orbital)

what are homonuclear diatomic molecules

diatomic molecules where several types of molecular orbitals ocuur

what is the linear combination of atomic orbital (LCAO)

the mathematical process of combing

what are molecular obitals

combinations of atomic orbital wave functions

what can combining waves lead to

constructive interference or destructive interference

what is constructive interference

peaks line up with peaks

increases electron density

what is destructive interference

peaks line up with troughs

creates nodes

decreases electron density

what are sigma s molecular orbitals

the in phase combination which is of lower energy and most of the electron density is directly between the nuclei

bonding orbital

more stable

what are sigma s* molecular orbitals

the out of phase addition ( can also be though of as subtracting the wave functions) which is of higher energy with a node between the nuclei

antibonding orbital

what is a bonding orbital

A molecular orbital formed by the constructive interference of atomic orbitals, resulting in lower energy and increased stability. It has electron density concentrated between the nuclei of the bonded atoms.

what is an antibonding orbital

A molecular orbital formed by the destructive interference of atomic orbitals, resulting in higher energy and decreased stability. It has a node between the nuclei, with electron density located outside the region between the bonded atoms.

what do p orbitals create when they overlap

sigma and sigma* orbitals

if the atoms are along the x-axis the two px orbitals overlap end to end to form sigma px and sigma*px orbitals

what does the side by side overlap of two p orbitals create

pi bonding molecular orbital and a pi antibonding molecular orbital.

what are pi bonds

contains a nodal plane with the internuclear axis and is perpendicular to the lobes of p-pi orbitals, with electron density on either side of the node.

a pi bond exists when this orbital contains electrons

the electrons interact with both nuclei and help hold the atoms together

what do molecular orbitals or diatomic molecules contain

each atom with two sets of p orbitals oriented side by side (py and pz)

what do the 2 sets of py and pz combine to create

two pi orbitals and two pi* orbitals

the pi py and pi*pz orbitals are oriented at right angles to the sigmapz and pi*pz orbtials

what are degenerate orbitals

orbitals that have the same energy

ex) sigma py and sigma pz

what are the six molecular orbitals that result from the combination of the 6 atomic p orbitals in two atoms

sigma px and sigma*px

pi py and pi* py

sigma pz and pi* pz

what is a molecular orbital energy diagram

A graphical representation that shows the relative energy levels of molecular orbitals formed from atomic orbitals. It illustrates how atomic orbitals combine to form bonding, antibonding, and nonbonding molecular orbitals.

what do horizontal lines on the molecular orbital energy diagrams represent

one orbital that can hold two electrons

what do dashed lines show on the molecular orbital energy diagrams?

which of the atomic orbitals combine to form the molecular orbitals

what do a pair of atomic orbitals combining produce

the lower energy (bonding) and higher energy (anti bonding)

ex) combining six 2p orbitals results in three bonding orbitals one sigma and two pi and three antibonding orbitals one sigma* and two pi*

why do we use the aufbau principle?

to predict the distribution of electrons in molecular orbitals

lower energy orbitals fill first, electrons spread out among degenerate orbitals before pairing

each orbital can hold a maximum of two electrons with opposite signs

how can tou write the molecular electronic configuration

listing the orbitals with superscripts indicating the number of electrons present

*place parenthesis around molecular orbitals with same energy

what is bond order?

Bond order is a measure of the stability of a bond, calculated as the difference between the number of bonding and antibonding electrons, divided by two. It indicates the strength and number of bonds between two atoms; for example, a bond order of 1 represents a single bond.

what is the bond order for a single bond, double bond, and triple bond?

1, 2, and 3

what is the equation for bond order?

for atoms with three or fewer electrons in the p orbitals (Li through N) what is the pattern observed?

the sigma p orbital is higher in energy than the pi p set

what is s-p mixing

change that cause sigma p orbitals to be less stable than pi p orbitals die to the mixing of s and p orbitals, affecting molecular stability.

also happens with sigma* p and pi* p orbitals

the turlets broken