Grade 10 Academic Science – Chemistry
Covalent Bond
Covalent Bond
 Covalent bonds are forces that hold atoms together. The forces are formed when the atoms of a
molecule share electrons.
 The bonds are strong. The exception is hydrogen bonds (see below).
There are two types of covalent bonds: (1) Polar Covalent and (2) Non-polar Covalent.
In a non-polar covalent bond, the electrons are shared equally by the adjacent
atoms. As a consequence, there is NO CHARGE SEPARATION between
atoms. Since there is no charge separation in the covalent bonds, this
molecule cannot enter into a charge interaction with water. Thus, a non-polar
covalently—bonded molecule is hydrophobic (i.e., cannot form hydrogen bonds with
water). These molecules are primarily hydrocarbons composed of hydrogen
and carbon atoms. Other examples are fatty acids, phospholipids and
cholesterol.
In a polar covalent bond, the electrons are NOT shared equally by the atoms. Rather, the shared
electrons spend a greater amount of time closer to one nucleus than the other nucleus. In the example of
water, the shared electrons are closer to the oxygen nucleus than the hydrogen
nucleus.
Why? There is a significant difference in the electron affinity between the
oxygen
and hydrogen. As a result, the oxygen has a partial negative
charge
and the two hydrogen have a partial positive charge.
NOTE: This is not an ionic bond because the
electrons are shared, Instead, there is a simple
charge separation. Peptides and amines are also
polar covalent. Biologically, polar covalent molecules form
weak hydrogen bonds – a bond formed when a charged part of
a molecule forms an electrostatic interaction with a
substance of opposite charge (positive attracted
to negative). As a result, they degrade or break
apart easily and they are hydrophilic (i.e., form a
charged interaction with the water molecules).