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8.4 Molecular Orbital Theory
Two hybridized, independently of which resonance form is considered.
The formation of sulfuric acid is the result of the reaction of sulfur dioxide with water.
Sulfur dioxide, SO2, is a major component of volcanic gases, as well as a product of the combustion of sulfur-containing coal.
The sulfur atom is surrounded by two bonds and one pair of electrons.
nitric acid, HNO3 is produced by the reaction of nitrogen dioxide, NO2, with atmospheric water vapor.
We can draw the Lewis structure, predict the electron-pair geometry, and come close to predicting bond angles for almost every covalent molecule.
The oxygen molecule O2 has a problem with its Lewis structure.
The electronic structure is in line with the rules of Lewis theory.
Each oxygen atom has eight electrons around it, and there is an O O double bond.
The magnetic behavior of oxygen is at odds with this picture.
O2 is attracted to magnetic fields.
The Lewis structure of O2 indicates that all electrons are pairs.
Magnetic susceptibility is the force experienced by a substance in a magnetic field.
Paramagnetic samples that are attracted to the magnet will appear heavier when compared to the weight measured in a magnetic field.
The increase in weight can be used to calculate the number of unpaired electrons.
A Gouy balance compares the mass of a sample in the presence of a magnetic field with the mass with the electromagnet turned off to determine the number of unpaired electrons.
There are two unpaired electrons in each O2 molecule.
The Lewis-structure model can't predict the presence of unpaired electrons.
In the presence of an inhomogeneous magnetic field, the apparent weight of most Molecules decreases slightly.
Paramagnetic and diamagnetic materials are not permanent magnets.
They can only show attraction or repulsion in the presence of a magnetic field.
Water has all thepaired electrons.
Living things have a large amount of water.
A frog will levitate if it is placed near a large magnet.
There are floating frog, strawberries, and more.
The paramagnetism of the oxygen molecule is explained by chemical bonding in the Mo theory.
It also explains the bonding in a number of other molecules, such as violations of the octet rule and more molecule with more complicated bonding, that are difficult to describe with Lewis structures.
It gives a model for describing the electrons in a molecule and their probable location.
Some substances are electrical conductors, others are semiconductors, and still others are insulators, thanks to MO theory.
The two bonding theories are summarized in Table 8.2.
Both theories give different ways of describing the structure.
Like electrons around isolated atoms, electrons around atoms in Molecules are limited to quantized energies.
When there are two electrons with the same spin, a molecule is full.
There are two identical atoms in a molecule.
There are several types of molecular orbitals in these diatomic molecules.
The wave function shows the wavelike properties of an electron.
There are combinations of atomic wave functions.
The waves are three-dimensional, and they combine with in-phase waves producing regions with a higher probability of electron density.
The orbital is an antibonding one.
The region between the two nuclei is close to the orbitals.
The two nuclei are pulled apart by the attractive force of the electrons.
Just as they fill lower-energy atomic orbitals before they fill higher-energy atomic orbitals, electrons fill the lower-energy bonding orbital before the higher-energy antibonding orbital.
The locations are indicated by the plus signs.
You can watch a visualization of the calculated atomic orbitals.
The phases are indicated by shading the orbital lobes.
Constructive wave interference increases the electron density when the same phase overlaps.
The destructive wave interference causes the regions of opposite phase to overlap.
A higher-energy, antibonding orbital is indicated by the asterisk.
When the p orbital contains electrons, there is a p bond.
The two atoms are held together by the help of electrons in this orbital.
There are two nodal planes created, one along the internuclear axis and the other between the nuclei, for the out-of-phase combination.
Combining the out-of-phase orbitals results in an antibonding orbital.
One is parallel to the axis and the other is not.
A bonding orbital is achieved by combining the in-phase orbitals.
The internuclear axis is located in a blue area near the two lobes of the orbital.
The antibonding orbitals are both degenerate and identical.
Predict what type of orbital would result from adding wave functions so each pair of orbitals shows up.
All of the orbitals have the same energy.
Only the correct alignment of the orbitals can combine.
It is a s orbital because it is located along the internuclear axis.
The internuclear axis is being bisected by an antibonding orbital.
Walter Kohn is a theoretical physicist.
The principles of quantum mechanics are combined with advanced mathematical techniques.
The density functional theory makes it possible to compute the properties of orbitals.
The chemistry prize was won by John Pople and Kohn in 1998 for their contributions to electronic structure.
Significant contributions to the physics of semiconductors were made by Kohn.
Walter Kohn was the first to develop methods to describe the structure of the atom.
He was part of the program that saved 10,000 children from the Nazis during World War II.
He discovered gold deposits in Canada and helped explain how instant film works.
He is still working on projects related to global warming and renewable energy.
There are many practical, real-world applications in the descriptions of bonding described in this chapter.
Drug design uses our understanding of chemical bonding to develop pharmaceuticals.
This area of study uses biology to identify specific targets, such as a binding site that is involved in a disease pathway.
Computational chemists can predict which structures will fit together and how effectively they will bind by modeling the binding site and potential drugs.
Candidate molecules are tested to determine side effects, how effectively they can be transported through the body, and other factors.
Computational chemistry has aided in the discovery of dozens of important new pharmaceuticals.
An important target for pharmaceutical research is the molecule shown.
Scientists have been able to greatly reduce the progress of the disease by designing molecule that bind to thisprotein.
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