Properties of Ionic Compounds
- Solid ionic compounds do not conduct an electric current.
- Molten samples of ionic compounds can conduct an electric
current due to the mobility of the ions which are free to move
to the electrodes and react.
- Ionic compounds have high melting and boiling points.
- Many ionic compounds can dissolve in water.
- Dissolved ionic compounds separate into cations and anions
- The mobile ions move to the electrodes and react to accept
and release electrons creating a flow of electricity in the
- Ionic compounds that are water soluble are strong electrolytes.
Molecular compounds form when two or more nonmetal atoms form units
that are called molecules. Molecular compounds generally have low
melting and boiling points. Molecular compounds do not conduct electricity
in the solid form or in the liquid form. Some molecular compounds
dissolve in water and some do not.
The proposed model for molecular compounds is that atoms of nonmetallic
elements can bond by sharing electrons to form units called molecules.
A very common example is the water molecule that forms when an oxygen
atom shares electrons with two hydrogen atoms to form one unit that
is called a water molecule. A sample of water is thought to be a
set of these molecular units.
Molecules are attracted to other molecules by attractions that
are called Intermolecular Attractions (attractions between
molecules). In a physical change such as melting or evaporation
these intermolecular attractions must be broken. Each molecule is
still a molecular unit but it is separated from the other molecular
units. Intermolecular attractions are generally weaker attractions
and do not require as much energy to break as do metallic, ionic
or covalent bonds. Therefore, molecular compounds generally have
low melting points and low boiling points.
Molecules may be polar molecules which have a charge separation
due to the shape of the molecule and the polarity of the bonds between
the atoms forming the molecule. These molecules are pictured as
having a positive end and a negative end and are said to be dipoles
or polar molecules. Other molecules are non-polar molecules.
These are molecules that have no charge separation again due to
the shape of the molecule and the polarity of the bonds between
the atoms forming the molecule. These non-polar molecules
are pictured as having no dipole character.
LIKE DISSOLVES LIKE. Polar molecules tend to dissolve materials
with charged nature such as ionic compounds and other polar molecules.
Likewise, non-polar molecules tend to dissolve other non-polar molecules.
Properties of Molecular Compounds
- Solid molecular compounds do not conduct an electric current.
- Molten samples of molecular compounds do NOT conduct electricity.
- Molecular compounds have low melting and boiling points.
- Polar molecular compounds can dissolve in water. Some very
polar molecular compounds can be "ripped" into ions
by the water molecules. These are said to be "dissociated"
into ions by the dipole nature of the water molecules.
- Polar molecular compounds are usually not soluble in non-polar
- Non-polar molecular compounds are usually not soluble in water.
They are soluble in other non-polar solvents such as toluene
and other organic solvents.
- Polar molecular compounds that are dissociate into ions by