ELECTRONEGATIVITY
Definition
Electronegativity is a measure of the tendency of an atom to attract
a bonding pair of electrons.
The Pauling scale is the most commonly used. Fluorine (the most
electronegative element) is assigned a value of 4.0, and values
range down to caesium and francium which are the least
electronegative at 0.7.
What happens if two atoms of equal electronegativity bond
together?
Consider a bond between two atoms, A and B.
If the atoms are equally electronegative, both have the same
tendency to attract the bonding pair of electrons, and so it will be
found on average half way between the two atoms. To get a bond
like this, A and B would usually have to be the same atom. You will
find this sort of bond in, for example, H2 or Cl2 molecules.
This sort of bond could be thought of as being a "pure" covalent
bond - where the electrons are shared evenly between the two
atoms-NON POLAR COVALENT.
What happens if B is slightly more electronegative than A?
B will attract the electron pair rather more than A does.
That means that the B end of the bond has more than its fair share
of electron density and so becomes slightly negative. At the same
time, the A end (rather short of electrons) becomes slightly positive.
Defining polar bonds
This is described as a polar bond. A polar bond is a covalent bond
