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Lesley Agyemang
Electronegativity and Intermolecular forces
Electronegativity is a measure of the attraction of a bonded atom for the pair
of electrons in covalent bonds. Molecules that have unequal sharing of
electrons are called polar molecules and dipole molecules are ones which
have the charge separated, therefore all polar molecules must have a dipole
attraction. Non-polar molecules are ones in which there shapes are
symmetrical so the electrons are evenly distributed. Polar molecules have a
permanent dipole in other words they have a permanent separation of
charge. As a result of this, polar molecules are attracted to one another by
forces called permanent dipole-permanent dipole interactions, in which the
negative end of one molecule is attracted towards the positive end of another.
These interactions decrease quite rapidly as the distance between molecules
Example: Hydrochloric Acid ­ HCl
In HCl, Chlorine is more electronegative than Hydrogen,
so it has a greater attraction for the electrons. This
means that the HCl molecule is polar with a permanent
Therefore, Hydrogen is + and Chlorine is - as shown in
figure 1
Another example is: Hydrogen - H2
As the 2 atoms are identical, they will have
the same number of protons, this means
that the electrons are being 'pulled'
equally by both of the hydrogen atoms, we
tend to say that the H - H bond is non-polar. The same is true for any diatomic
`molecule where the atoms are identical as shown in
figure 2
In symmetrical molecules, dipoles cancel and there
is no overall permanent dipole
For example; CCl4 (Tectrachloromethane) It has
polar covalent bonds. We say there is no overall
dipole as the dipoles act in different directions and
cancel each other out (because it is symmetrical).
Basically, there is not a positive end and a negative end. As shown in figure 3

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Lesley Agyemang
Electronegativity is measured using the Pauling scale which was invented by
a US chemist called Linus Pauling in 1932. The Pauling scale was used to
measure the Electronegativity of an atom. Going across a period, the nuclear
charge increases and the size of the atom decreases these results in an
increase in electronegativity. Going down a group, the value of
electronegativity decreases since the atoms increase in size. Most
electronegative element is Fluorine (non-metal), whereas the least
electronegative element is Francium (metal).…read more

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Lesley Agyemang
Intermolecular force is an attractive force between neighbouring molecules.
There are three types of intermolecular forces: Van der Waal's forces, Permanent
dipole-dipole forces, Hydrogen bonding
Vans der Waal's force is forces that attract forces between induced dipoles in
neighbouring molecules. In Van der Waal's forces atoms has temporary induced
dipole which is caused by the movement of electrons within atoms- unbalances
distribution of charge within electron shells.…read more

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Lesley Agyemang
Water has three special properties due to hydrogen bonding which are: ice is
less dense than water; water has relatively high melting + boiling points and
surface tension.
Ice is less dense than water:
Ice has open lattice with hydrogen bonds holding water molecules apart, when
ice melts, rigid hydrogen bonds break allowing the HO molecules to move closer
together.…read more


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