3.3 Electronegativity (ESBMD)

So much we have looked in ~ covalent molecules. But how perform we recognize that they space covalent? The answer comes from electronegativity. Each facet (except because that the noble gases) has an electronegativity value.

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Electronegativity is a measure of exactly how strongly an atom pulls a mutual electron pair towards it. The table below shows the electronegativities of the several of the elements.

For a full list that electronegativities watch the routine table in ~ the former of the book. ~ above this regular table the electronegativity worths are offered in the height right corner. Execute not confuse these values through the various other numbers displayed for the elements. Electronegativities will always be in between ( ext0) and also ( ext4) for any kind of element. If you usage a number better than ( ext4) then you room not utilizing the electronegativity.





Hydrogen (( extH))

( ext2,1)

Lithium (( extLi))

( ext1,0)

Beryllium (( extBe))

( ext1,5)

Boron (( extB))

( ext2,0)

Carbon (( extC))

( ext2,5)

Nitrogen (( extN))

( ext3,0)

Oxygen (( extO))

( ext3,5)

Fluorine (( extF))

( ext4,0)

Sodium (( extNa))

( ext0,9)

Magnesium (( extMg))

( ext1,2)

Aluminium (( extAl))

( ext1,5)

Silicon (( extSi))

( ext1,8)

Phosphorous (( extP))

( ext2,1)

Sulfur (( extS))

( ext2,5)

Chlorine (( extCl))

( ext3,0)

Potassium (( extK))

( ext0,8)

Calcium (( extCa))

( ext1,0)

Bromine (( extBr))

( ext2,8)


Electronegativity is a chemical building which describes the strength of one atom to attract electrons towards itself.

The ide of electronegativity was presented by Linus Pauling in 1932, and also this became really useful in explaining the nature that bonds in between atoms in molecules. Because that this work, Pauling to be awarded the Nobel prize in Chemistry in 1954. He likewise received the Nobel peace Prize in 1962 for his campaign against above-ground nuclear testing.

The greater the electronegativity of one atom of an element, the stronger its attractive pull on electrons. Because that example, in a molecule of hydrogen bromide (( extHBr)), the electronegativity the bromine (( ext2,8)) is greater than the of hydrogen (( ext2,1)), and also so the shared electrons will certainly spend more of their time closer to the bromine atom. Bromine will have actually a slightly negative charge, and hydrogen will have actually a slightly hopeful charge. In a molecule prefer hydrogen (( extH_2)) whereby the electronegativities that the atom in the molecule room the same, both atoms have actually a neutral charge.

Worked instance 9: Calculating electronegativity differences

Read the electronegativity that each aspect off the routine table.

From the regular table we discover that hydrogen has actually an electronegativity the ( ext2,1) and oxygen has an electronegativity that ( ext3,5).

Calculate the electronegativity difference between: ( extBe) and ( extC), ( extH) and also ( extC), ( extLi) and ( extF), ( extAl) and ( extNa), ( extC) and also ( extO).

( extBe) and ( extC): ( ext2,5 - ext1,5 = ext1,0.)

( extH) and also ( extC): ( ext2,5 - ext2,1 = ext0,4.)

( extLi) and ( extF): ( ext4,0 - ext1,0 = ext3,0.)

( extAl) and also ( extNa): ( ext1,5 - ext0,9 = ext0,6.)

( extC) and also ( extO): ( ext3,5 - ext2,5 = ext1,0.)

Electronegativity and bonding (ESBMF)

The electronegativity difference between two atoms deserve to be supplied to identify what type of bonding exists between the atoms. The table listed below lists the approximate values. Although we have offered ranges right here bonding is much more like a spectrum 보다 a set of boxes.

Electronegativity difference Type that bond
( ext0) Non-polar covalent
( ext0) - ( ext1) Weak polar covalent
( ext1,1) - ( ext2) Strong polar covalent
(>) ( ext2,1) Ionic

Note that metallic bonding is not provided here. Metals have low electronegativities and also so the valence electrons room not attracted strongly to any type of one atom. Instead, the valence electrons space loosely shared by every the atom in the metallic network.

Non-polar and polar covalent bonds (ESBMG)

It is important to be able to determine if a molecule is polar or non-polar since the polarity of molecule affects nature such together solubility, melting points and also boiling points.

Electronegativity can be supplied to describe the difference in between two species of covalent bonds. Non-polar covalent bonds occur between two identical non-metal atoms, e.g. ( extH_2), ( extCl_2) and ( extO_2). Since the 2 atoms have the exact same electronegativity, the electron pair in the covalent link is mutual equally between them. However, if two various non-metal atom bond then the common electron pair will certainly be pulled more strongly through the atom v the greater electronegativity. Together a result, a polar covalent bond is developed where one atom will have a slightly an unfavorable charge and the various other a slightly hopeful charge.

This slightly hopeful or slightly an unfavorable charge is recognized as a partial charge. These partial dues are represented using the signs (delta ^+) (slightly positive) and (delta ^-) (slightly negative). So, in a molecule such as hydrogen chloride (( extHCl)), hydrogen is ( extH^delta^+) and chlorine is ( extCl^delta^-).

Polar molecules (ESBMH)

Some molecules through polar covalent bonds space polar molecules, e.g. ( extH_2 extO). Yet not all molecules through polar covalent bonds are polar. An example is ( extCO_2). Back ( extCO_2) has actually two polar covalent binding (between ( extC^delta^+) atom and also the 2 ( extO^delta^-) atoms), the molecule chin is no polar. The reason is that ( extCO_2) is a direct molecule, through both terminal atom the same, and is thus symmetrical. So over there is no distinction in charge in between the two ends the the molecule.

Polar molecules

A polar molecule is one that has one finish with a slightly positive charge, and one finish with a slightly an adverse charge. Examples incorporate water, ammonia and also hydrogen chloride.

Non-polar molecules

A non-polar molecule is one wherein the fee is equally spread throughout the molecule or a symmetry molecule with polar bonds. Examples include carbon dioxide and also oxygen.

To identify if a molecule is symmetry look very first at the atoms around the main atom. If they are different then the molecule is not symmetrical. If they space the same then the molecule may be symmetrical and we must look at the form of the molecule.

We can quickly predict which molecules are likely to it is in polar and also which are likely to be non-polar by looking in ~ the molecule shape. The following activity will aid you determine this and will assist you understand more about symmetry.

Polar and also non-polar molecules

The complying with table list the molecular shapes. Build the molecule provided for each case using jellytots and toothpicks. Recognize if the shape is symmetrical. (Does it look the exact same whichever method you look in ~ it?) now decide if the molecule is polar or non-polar.



Bent or angular

Trigonal planar

Trigonal planar

Trigonal pyramidal



Trigonal bipyramidal

Trigonal bipyramidal






Polar or non-polar


( extHCl)

( extCO_2)
( extHCN)

( extH_2 extO)

( extBF_3)

( extBF_2 extCl)

( extNH_3)

( extCH_4)

( extCH_3 extCl)

( extPCl_5)

( extPCl_4 extF)

( extSF_6)

( extSF_5 extCl)

Simulation: 23PR

Worked instance 10: Polar and non-polar molecules

State whether hydrogen (( extH_2)) is polar or non-polar.

Determine the shape of the molecule

The molecule is linear. There is one bonding pair of electrons and no lone pairs.

Determine the electronegativity difference for every bond

There is just one bond and the difference is ( ext0).

Determine the form of each molecule

The molecule is tetrahedral. There are 4 bonding pairs of electrons and no lone pairs.

Determine the electronegativity difference for each bond

There are 4 bonds. Due to the fact that each link is between carbon and also hydrogen, we only need to calculate one electronegativity difference. This is: ( ext2,5 - ext2,1 = ext0,4)

Determine the shape of the molecule

The molecule is linear. Over there are four bonding pairs, three of which type a triple bond and so space counted as ( ext1). There is one lone pair top top the nitrogen atom.

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Determine the electronegativity difference and also polarity because that each bond

There space two bonds. One in between hydrogen and also carbon and also the other between carbon and also nitrogen. The electronegativity difference between carbon and hydrogen is ( ext0,4) and the electronegativity difference in between carbon and nitrogen is ( ext0,5). Both the the bonds space polar.