# 0.5 Molecular geometry and electron domain theory

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## Foundation

We begin by assuming a Lewis structure model for chemical bonding based on valence shell electron pair sharing and the octet rule. We thusassume the nuclear structure of the atom, and we further assume the existence of a valence shell of electrons in each atom whichdominates the chemical behavior of that atom. A covalent chemical bond is formed when the two bonded atoms share a pair of valenceshell electrons between them. In general, atoms of Groups IV through VII bond so as to complete an octet of valence shellelectrons. A number of atoms, including C, N, O, P, and S, can form double or triple bonds as needed to complete an octet. We know thatdouble bonds are generally stronger and have shorter lengths than single bonds, and triple bonds are stronger and shorter than doublebonds.

## Goals

We should expect that the properties of molecules, and correspondingly the substances which they comprise,should depend on the details of the structure and bonding in these molecules. The relationship between bonding, structure, andproperties is comparatively simple in diatomic molecules, which contain two atoms only, e.g. $H\mathrm{Cl}$ or ${O}_{2}$ . A polyatomic molecule contains more than two atoms. An example of the complexities which arise with polyatomic moleculesis molecular geometry: how are the atoms in the molecule arranged with respect to one another? In a diatomic molecule, only a singlemolecular geometry is possible since the two atoms must lie on a line. However, with a triatomic molecule (three atoms), there aretwo possible geometries: the atoms may lie on a line, producing a linear molecule, or not, producing a bent molecule. In moleculeswith more than three atoms, there are many more possible geometries. What geometries are actually observed? What determineswhich geometry will be observed in a particular molecule? We seek a model which allows us to understand the observed geometries ofmolecules and thus to predict these geometries.

Once we have developed an understanding of the relationship between molecular structure and chemical bonding, wecan attempt an understanding of the relationship of he structure and bonding in a polyatomic molecule to the physical and chemicalproperties we observe for those molecules.

## Observation 1: geometries of molecules

The geometry of a molecule includes a description of the arrangements of the atoms in the molecule. At asimple level, the molecular structure tells us which atoms are bonded to which. At a more detailed level, the geometry includesthe lengths of all of these bonds, that is, the distances between the atoms which are bonded together, and the angles between pairsof bonds. For example, we find that in water, ${H}_{2}O$ , the two hydrogens are bonded to the oxygen and each O-H bond lengthis 95.72pm (where $1\mathrm{pm}=10^{-12}m$ ). Furthermore, ${H}_{2}O$ is a bent molecule, with the H-O-H angle equal to 104.5°. (The measurement of these geometric properties is difficult,involving the measurement of the frequencies at which the molecule rotates in the gas phase. In molecules in crystalline form, thegeometry of the molecule is revealed by irradiating the crystal with x-rays and analyzing the patterns formed as the x-raysdiffract off of the crystal.)

#### Questions & Answers

what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
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
what is the stm
Brian Reply
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?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
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
what is Nano technology ?
Bob Reply
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?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, General chemistry i. OpenStax CNX. Jul 18, 2007 Download for free at http://cnx.org/content/col10263/1.3
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