# 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.

where we get a research paper on Nano chemistry....?
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
ya I also want to know the raman spectra
Bhagvanji
I only see partial conversation and what's the question here!
what about nanotechnology for water purification
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
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?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
how did you get the value of 2000N.What calculations are needed to arrive at it
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