S-Cool Revision Summary

S-Cool Revision Summary

Atoms are most stable if they have a full outer shell.

Atoms bond with one another to achieve full outer shells - this is why most
elements form compounds.

Noble gases do not form compounds, since they already have full outer
shells.

Metal atoms (and hydrogen), such as sodium, lose electrons to
become ions. Ions are charged particles. Since metals lose electrons
to achieve full outer shell configurations, the metal ions have positive
charges
. A positive ion is called a cation.

Non-metal atoms, such as chlorine, gain electrons and become
ions. By gaining electrons they can achieve a full outer shell. Since they gain
electrons non-metal ions have negative charges. A negative ion is called
an anion.

Metal atoms bond with non-metal ions by transferring their electrons.
This is called ionic bonding.

For some elements, the energy involved in losing or gaining electrons is too
much. In these cases their atoms share electrons. This bonding associated
with the sharing of electrons is called covalent bonding.

There are four types of solid, giant ionic, giant covalent, metallic and
simple molecular
.

Sodium chloride is an example of a giant ionic solid. It consists of
oppositely charged ions held together by electrostatic forces. They are soluble
in water and conduct electricity when molten or in solution.

Diamond and graphite are examples of giant (covalent) molecular solids.
They consist of millions of covalent bonds that cause them to have very high
boiling points.

Iodine is an example of a simple molecular solid. It has a low boiling
point because molecules of I2 are held together by weak forces.
They are insoluble in water and do not conduct electricity.

Metals consist of tightly packed atoms whose outer electrons become
part of a ' sea ' of electrons. This delocalisation of electrons explains
why metals are good conductors of heat and electricity.