AS chemistry- Electronegativity and polarity

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  • Created on: 17-11-12 21:35
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Electronegativity and polarity
key definitions
electronegativity a measure of the attraction of a bonded atom for the pair of
electrons in a covalent bond.
permanent dipole a small charge difference across a bond, that is formed from
a difference in electronegativities of the bonded atoms.
polar molecule a nonsymmetrical molecule, with an overall dipole.
nonpolar molecule a symmetrical molecule, without an overall
polar and nonpolar bonds (if you are finding this tricky picture it as a tug of
war, it really helps!)
as you know a covalent bond is formed from a shared pair of electrons. for
example, in a H2 molecule the bonding atoms are identical, so they equally
share the electrons, resulting in an even covalent bond.
this HH bond is said to be NONPOLAR as the electrons in the covalent bond
are evenly distributed between the atoms which make the bond.
however, in a molecule of HCl, the two bonding atoms are different.
as the Cl has more electrons than the H atom, it is said to be MORE
electronegative than the H atom.
as the Cl atom is more electronegative than the H atom, the Cl atom has a
greater attraction for the bonding pair of electrons than the H atom.
this makes the bonding pairs closer to the Cl atom than the H atom.
As the electron pair is closer to the Cl than the H atom (like a tug of war) there is
this small charge difference is called a permanent dipole
the HCl bond is said to be a polar covalent bond, as it is a covalent bond
between polar molecules, as it has a permanent dipole.

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H atom)
a small negative charge (delta negative) on the more elctronegative atom (in this
case the Cl atom)
(as the dipoles do not cancel out)
(as the dipoles do cancel out!)
did you know: it's possible to have a nonpolar
molecule, even if it contains permanent dipoles!
lets take for example a CCl4 molecule.…read more

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Electronegativity is a measure of the attraction between the bonded atom
and pair of electrons in a covalent bond.
Electronegativity is measured using the Pauling scale (which was invented
by the chemist Linus Pauling in 1932)
Electronegativity increases towards the top right of the periodic
table, with fluorine being the most electronegative atom.
N, O & F are the most electronegative elements in the periodic table.
You must know their approximate electronegative values for the exam
, these are.…read more

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Pauling scale
the approximate electronegativity values for F,O,N…read more


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