Covalent Bonds Covalent Bonds

							          Covalent Bonds
  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?
              Covalent Bond
• 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.
                    Molecule
• 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.
                Molecular Compound
                • A molecular compound is a
                  compound that is composed of
                  molecules.
                • Molecular compounds have very
                  different properties than ionic
                  compounds.
                • Compared to ionic compounds,
                  molecular compounds have
                  lower melting points & boiling
Sodium Iodide     points, and they do not conduct
                  electricity.
Polar Bonds

• Atoms of some elements pull more strongly on
  shared electrons than do atoms of other
  elements.
• 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
  ions.
• A covalent bond in which electrons are shared
  unequally is a polar bond.
           Non Polar Bond
• When the
  valence electrons
  are shared
  equally, the bond
  is non polar.
             Nonpolar Bonds
• 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
• 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
  compounds.
• 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.