(adapted from http://en.wikipedia.org/wiki/Chemical_bond)

covalent bonding
involves the
sharing
of electrons

the positively charged
nuclei of two or more atoms
simultaneously attract the
negatively charged electrons
that are being shared
between
them.

in a so-called ‘covalent’ bond,
one or more electrons are drawn
into the space between two atomic nuclei.

the negatively charged electrons are attracted
to the positive charges of both nuclei,
instead of just their own.

this overcomes
the repulsion
between the two
positively charged
nuclei,
as this
overwhelming
attraction holds
the two nuclei
in a fixed
configuration

even though
they will
still vibrate
at
equilibrium
position.

a less often
mentioned
type of bond
is the metallic bond.

In this type of bonding,
each atom
donates one
or more electrons to
a “sea” of electrons

that
reside
between
many metal
atoms.

In this sea, each electron is free
(by virtue of its wave nature) to be
associated with a great many atoms
at once. The bond results because
the metal atoms become positively
charged
due to loss
of their electrons,
while the electrons remain
attracted to many atoms,
without being part

of
any
given
atom.

in an ionic bond, the bonding
electron is not shared at all,
but transferred.

In this type
of bond, the
outer atomic orbital
of one atom has
a vacancy

which allows
addition of
one or more
electrons.

these newly added electrons
potentially occupy a lower
energy-state (effectively
closer to more nuclear charge)

than they experience in a
different atom. Thus, one
nucleus offers a more tightly
bound position
to an electron
than does another
nucleus, with the result
that one atom may transfer
an electron to the other.

This transfer
causes one atom
to assume a
net positive charge,
and the other
to assume a
net negative charge.

For further reading, refer to: “Jane Eyre” by Charlotte Bronte