# 3.11 Molecular orbital theory  (Page 9/26)

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## Molecular orbital diagrams, bond order, and number of unpaired electrons

Draw the molecular orbital diagram for the oxygen molecule, O 2 . From this diagram, calculate the bond order for O 2 . How does this diagram account for the paramagnetism of O 2 ?

## Solution

We draw a molecular orbital energy diagram similar to that shown in [link] . Each oxygen atom contributes six electrons, so the diagram appears as shown in [link] .

We calculate the bond order as

${\text{O}}_{2}=\phantom{\rule{0.2em}{0ex}}\frac{\left(8-4\right)}{2}\phantom{\rule{0.2em}{0ex}}=2$

Oxygen's paramagnetism is explained by the presence of two unpaired electrons in the (π 2 py , π 2 pz )* molecular orbitals.

The main component of air is N 2 . From the molecular orbital diagram of N 2 , predict its bond order and whether it is diamagnetic or paramagnetic.

N 2 has a bond order of 3 and is diamagnetic.

## Ion predictions with mo diagrams

Give the molecular orbital configuration for the valence electrons in ${\text{C}}_{2}{}^{\text{2−}}.$ Will this ion be stable?

## Solution

Looking at the appropriate MO diagram, we see that the π orbitals are lower in energy than the σ p orbital. The valence electron configuration for C 2 is ${\left({\text{σ}}_{2s}\right)}^{2}{\left({\text{σ}}_{\text{2}s}^{*}\right)}^{2}{\left({\text{π}}_{2py},\phantom{\rule{0.2em}{0ex}}{\text{π}}_{2pz}\right)}^{4}.$ Adding two more electrons to generate the ${\text{C}}_{2}{}^{\text{2−}}$ anion will give a valence electron configuration of ${\left({\text{σ}}_{2s}\right)}^{2}{\left({\text{σ}}_{\text{2}s}^{*}\right)}^{2}{\left({\text{π}}_{2py},\phantom{\rule{0.2em}{0ex}}{\text{π}}_{2pz}\right)}^{4}{\left({\text{σ}}_{2px}\right)}^{2}.$ Since this has six more bonding electrons than antibonding, the bond order will be 3, and the ion should be stable.

How many unpaired electrons would be present on a ${\text{Be}}_{2}{}^{\text{2−}}$ ion? Would it be paramagnetic or diamagnetic?

two, paramagnetic

## Key concepts and summary

Molecular orbital (MO) theory describes the behavior of electrons in a molecule in terms of combinations of the atomic wave functions. The resulting molecular orbitals may extend over all the atoms in the molecule. Bonding molecular orbitals are formed by in-phase combinations of atomic wave functions, and electrons in these orbitals stabilize a molecule. Antibonding molecular orbitals result from out-of-phase combinations of atomic wave functions and electrons in these orbitals make a molecule less stable. Molecular orbitals located along an internuclear axis are called σ MOs. They can be formed from s orbitals or from p orbitals oriented in an end-to-end fashion. Molecular orbitals formed from p orbitals oriented in a side-by-side fashion have electron density on opposite sides of the internuclear axis and are called π orbitals.

We can describe the electronic structure of diatomic molecules by applying molecular orbital theory to the valence electrons of the atoms. Electrons fill molecular orbitals following the same rules that apply to filling atomic orbitals; Hund’s rule and the Aufbau principle tell us that lower-energy orbitals will fill first, electrons will spread out before they pair up, and each orbital can hold a maximum of two electrons with opposite spins. Materials with unpaired electrons are paramagnetic and attracted to a magnetic field, while those with all-paired electrons are diamagnetic and repelled by a magnetic field. Correctly predicting the magnetic properties of molecules is in advantage of molecular orbital theory over Lewis structures and valence bond theory.

Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
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biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
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absolutely yes
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how to know photocatalytic properties of tio2 nanoparticles...what to do now
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for teaching engĺish at school how nano technology help us
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what is fullerene does it is used to make bukky balls
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s.
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what is the actual application of fullerenes nowadays?
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what is the Synthesis, properties,and applications of carbon nano chemistry
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is Bucky paper clear?
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carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
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so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
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what is biological synthesis of nanoparticles
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