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A table with four rows and six columns is shown. The header column contains the phrases, “Number of regions,” “Spatial arrangement,” “Wedge/dash Notation,” and “Electron pair Geometry.” The first row reads: “Two regions of high electron density ( bonds and/or unshared pairs )”, “Three regions of high electron density ( bonds and/or unshared pairs ),” “Four regions of high electron density ( bonds and/or unshared pairs ),” “Five regions of high electron density ( bonds and/or unshared pairs ),” and “Six regions of high electron density ( bonds and/or unshared pairs ).” The second row shows diagrams of orbitals. The first image shows two oval-shaped orbs with an arrow indicating an angle of 180 degrees. The second image shows three oval-shaped orbs with an arrow indicating an angle of 120 degrees. The third image shows four oval-shaped orbs with an arrow indicating an angle of 109.5 degrees. The fourth image shows five oval-shaped orbs with an arrow indicating an angle of 90 and 120 degrees. The fifth image shows six oval-shaped orbs with an arrow indicating an angle of 90 degrees. The third row contains Lewis structures. The first structure shows a beryllium atom single bonded to two hydrogen atoms. The second structure shows a boron atom single bonded to three hydrogen atoms. The third structure shows a carbon atom single bonded to four hydrogen atoms. The fourth structure shows a phosphorus atom single bonded to five fluorine atoms. The fifth structure shows a sulfur atom single bonded to six fluorine atoms. The fourth row contains the phrases “Linear; 180 degree angle,” Trigonal Planar; all angles 120 degrees,” “Tetrahedral; all angles 109.5 degrees,” “Trigonal bipyramidal; angles of 90 degrees and 120 degrees. An attached atom may be equatorial, ( in the plane of the triangle ), or axial, ( above the plane of the triangle ),” and “Octahedral; 90 degrees or 180 degrees.”
The basic electron-pair geometries predicted by VSEPR theory maximize the space around any region of electron density (bonds or lone pairs).

Electron-pair geometry versus molecular structure

It is important to note that electron-pair geometry around a central atom is not the same thing as its molecular structure. The electron-pair geometries shown in [link] describe all regions where electrons are located, bonds as well as lone pairs. Molecular structure describes the location of the atoms , not the electrons.

We differentiate between these two situations by naming the geometry that includes all electron pairs the electron-pair geometry    . The structure that includes only the placement of the atoms in the molecule is called the molecular structure    . The electron-pair geometries will be the same as the molecular structures when there are no lone electron pairs around the central atom, but they will be different when there are lone pairs present on the central atom.

For example, the methane molecule, CH 4 , which is the major component of natural gas, has four bonding pairs of electrons around the central carbon atom; the electron-pair geometry is tetrahedral, as is the molecular structure ( [link] ). On the other hand, the ammonia molecule, NH 3 , also has four electron pairs associated with the nitrogen atom, and thus has a tetrahedral electron-pair geometry. One of these regions, however, is a lone pair, which is not included in the molecular structure, and this lone pair influences the shape of the molecule ( [link] ).

A Lewis structure shows a carbon atom single bonded to four hydrogen atoms. This structure uses wedges and dashes to give it a three dimensional appearance.
The molecular structure of the methane molecule, CH 4 , is shown with a tetrahedral arrangement of the hydrogen atoms. VSEPR structures like this one are often drawn using the wedge and dash notation, in which solid lines represent bonds in the plane of the page, solid wedges represent bonds coming up out of the plane, and dashed lines represent bonds going down into the plane.
Three images are shown and labeled, “a,” “b,” and “c.” Image a shows a nitrogen atom single bonded to three hydrogen atoms. There are four oval-shaped orbs that surround each hydrogen and one facing away from the rest of the molecule. These orbs are located in a tetrahedral arrangement. Image b shows a ball-and-stick model of the nitrogen single bonded to the three hydrogen atoms. Image c is the same as image a, but there are four curved, double headed arrows that circle the molecule and are labeled, “106.8 degrees.”
(a) The electron-pair geometry for the ammonia molecule is tetrahedral with one lone pair and three single bonds. (b) The trigonal pyramidal molecular structure is determined from the electron-pair geometry. (c) The actual bond angles deviate slightly from the idealized angles because the lone pair takes up a larger region of space than do the single bonds, causing the HNH angle to be slightly smaller than 109.5°.

As seen in [link] , small distortions from the ideal angles in [link] can result from differences in repulsion between various regions of electron density. VSEPR theory predicts these distortions by establishing an order of repulsions and an order of the amount of space occupied by different kinds of electron pairs. The order of electron-pair repulsions from greatest to least repulsion is:

lone pair-lone pair > lone pair-bonding pair > bonding pair-bonding pair

This order of repulsions determines the amount of space occupied by different regions of electrons. A lone pair of electrons occupies a larger region of space than the electrons in a triple bond; in turn, electrons in a triple bond occupy more space than those in a double bond, and so on. The order of sizes from largest to smallest is:

Questions & Answers

please guys,I need questions on Dalton's law of partial pressure and Graham's law of diffusion
Godwin Reply
what is E cell?
Michelle Reply
what is hydrocarbon
Sensible Reply
this is an organic compound that consist of hydrogen and ox
Okafor
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Elaborate more pls
Adeyinka
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Elaine
what is hydrocarbon? pls
Sensible
Hydrocarbon are organic compound consisting of hydrogen and carbon atoms
Adeyinka
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Sensible
why is electrolytes really active in water
Sensible
relationship between an orbit and a shell
Hawa Reply
relationship between orbit and a shell
Hawa
What a homogenous mixture
Allison Reply
these are mixture of same substance or particles
INETIABOR
they are mixture of same particles or substance
INETIABOR
Define homologous series
Chizoba Reply
it is an organic compound having the same chemical properties which differs in a successive member of CH4
Okafor
when iron is exposed to moisture and it rusts,the value of deltaG for the reaction is
Mary Reply
negative
Max
table
Witszy
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it is a branch of science that deals with the mixture of chemicals and properties and uses of matter
Okafor
define aci according to Lewis
Ryhanna Reply
an acid is an electron pair acceptor according to lewis
Mary
What is a homogenous mixture
Allison
it is d mixture of d same substances or particle or compound
Okafor
homogenous is the combination or mixture of the same particle or compound
johnson
the third ionization energy of aluminium
sanmi Reply
name the allotrope of carbon used in gas masks
Moses Reply
Discuss the synthesis of sucrose
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What is a glycoside and discuss the formation
Ojiya
explain the transitioning of glucose molecules from Fischer projection of glucose to the Haworth projection
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hezekiah Reply
what are metalliod
hezekiah
Metalloids are substances having the characteristics of both metals and non-metals
Ngwesse
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Acid is an electron acceptor
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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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