What holds covalently bonded atoms together?
What are the properties of molecular compounds?
How does unequal sharing of electrons occur, & how
does it affect molecules?
• The chemical bond formed when two atoms
share electrons is called a covalent.
• Except for the noble gases, nonmetals can
bond to other non metals by sharing electrons
in covalent bonds.
• The force that holds atoms together in a
covalent bond is the attraction of each atom’s
nucleus for the shared pair of electrons.
• A neutral group of atoms joined by
covalent bonds is called a molecule.
• The number of covalent bonds a
nonmetal atom can form equals the
number of valence electrons needed
to make a total of eight.
• Some atoms share two pairs of
electrons, forming a double bond.
• Some atoms even form triple bonds
in which their atoms share three
pairs of electrons.
• A molecular compound is a
compound that is composed of
• Molecular compounds have very
different properties than ionic
• Compared to ionic compounds,
molecular compounds have
lower melting points & boiling
Sodium Iodide points, and they do not conduct
• Atoms of some elements pull more strongly on
shared electrons than do atoms of other
• As a result, the electrons are pulled more
toward one atom, causing the bonded atoms to
have slight electrical charges.
• These charges are not as strong as the charges on
• A covalent bond in which electrons are shared
unequally is a polar bond.
Non Polar Bond
• When the
equally, the bond
is non polar.
• A molecule is nonpolar if it contains only
nonpolar bonds, or if it has polar bonds that
cancel each other out.
• For ex. Carbon dioxide (CO2), the oxygen
atoms attract electrons more strongly than
the carbon atom does.
• However, the two oxygen atoms pull with
equal strength in opposite directions, so the
polar bonds cancel each other out.
• Polar molecules are more strongly attracted to each
other than are nonpolar molecules.
• This difference in the attraction between molecules
leads to different properties in polar & nonpolar
• Polar & nonpolar molecules also do not mix.
• For ex. Water, which is polar, does not mix with oil,
which is nonpolar.
• The nonpolar oil molecules have little attraction for the
polar water molecules, while the water molecules are
more strongly attrected to one another.