Polar bonds and electronegativity

Polar bonds and electronegativity


Covalent bonds can be defined as
purely covalent or polar covalent. Purely covalent is when — for example,
in the case of diatomic hydrogen, the electrons are shared equally
between the two atoms. A polar covalent bond is when the
electrons reside closer to one atom or another, as in the
case for hydrogen chloride. We would envision that because
chlorine is a more — has a higher electron affinity, the electrons
will reside more towards the chlorine. So in this case, they’re
not equally shared so we say that they are polar covalent.
It’s a polar covalent bond. The symbol with a partial symbol
and a plus, and a partial negative indicates that the electrons reside
more towards the chlorine atoms than the hydrogen atoms. This is
the symbol that’s used to show that the electrons are not equally
shared. There’s also — A vector is used pointing in the direction of the
atom in which the electrons tend to reside. So in this way, we know have a
pure covalent bond where the electrons are equally shared and
there’s no partial charge on either atom, or a polar covalent bond,
polar being two poles a positive pole and a negative pole. Now, it’s important to note that
there are different degrees of polarity, and so the electronegativity
scale was developed by Linus Pauling and others to help
quantify how polar a covalent bond is. As it turns out, the electronegativity
is based on both the ionization energy and the electron affinity
for the atom. And what we see is that in the upper right-hand
part of the periodic table, the atoms are more electronegative,
and in the lower left-hand corner they are less electronegative.
So that means that the atoms in this region of the periodic table
have a stronger attraction when bound covalently to another atom. So electronegativity is the attraction for
a pair of electrons in a covalent bond. So we use electronegativity to
understand the attraction of the electrons in a covalent bond. A greater value for electronegativity
means that it has a greater attraction. Now, to quantify how polar a bond
is, the electronegativity values have been assigned so this periodic table
shows the electronegativity values. Note, there are no values for the noble
gases because noble gases don’t tend to form covalent bonds and they
don’t have electron affinities or ionization energies that make any
sense in this context, so we just look at the elements that tend
to form bonds, whether they be ionic or covalent, and
the degree of polarity has to do with the difference in the
electronegativity values between the two atoms found in
the particular compound. For example, hydrogen chloride. The electronegativity value for
chlorine is 3.0, electronegativity value for hydrogen is 2.1, so for
hydrogen chloride, the difference in the electronegativity values
would be 3.0 minus 2.1 equals .9. Thus, for the hydrogen the
difference in electronegativity value is zero because the values
are the same. So, hydrogen chloride would be considered a
polar covalent bond. Hydrogen, diatomic molecular hydrogen,
would be considered a non-polar bond. Now, typically, if the
difference in electronegativity values is greater than 1.5,
then one considers that bond an ionic bond.
For example, if you look at calcium. Calcium
has electronegativity value of one, and oxygen has electronegativity
value of 3.5, so the difference in electronegativity for calcium oxide
is 2.5. So anytime the difference in electronegativity is greater than
1.5, it’s safe to consider that particular bond an ionic bond. Further, even — Let’s take for example,
the bond between carbon and hydrogen. The electronegativity difference between
carbon hydrogen is only .4 so we’d say that bond is non-polar or very, very
slightly polar compared to the HCl bond, which was a difference of .9. So, we have a way to compare the
differences in polarities of bonds. Some bonds being
more polar than others, based on the difference
in electronegativity values of those bonds.

One thought on “Polar bonds and electronegativity

Leave a Reply

Your email address will not be published. Required fields are marked *