Remember that what is important in chemical bonding is the outer
shell of the electrons of an atom.  An electron dot diagram is a
simplified way to show all of the information that is needed for
covalent bonding.

An electron dot diagram is made of the chemical symbol (see last
chapter if you forgot) and eight spaces for the electron spaces in the
outer shell (2 for hydrogen and helium).  Show at the right is a
sample with X's to represent the placement of the dots.
Here you see an electron dot diagram
of a diatomic hydrogen molecule.  
Notice that it has the chemical symbol
and the dots for the electrons, but the
shells are drawn in to show you that
the electrons are shared.  If you erase
the rings you have a true electron dot
diagram.
Shown here are four typical Electron dot
diagrams.  Again, notice how the elemental
symbols are the center and the number of
electrons in the outer shell (and only the outer
shell) are shown.

Remember: The only exception to exceptions to
the eight dots are hydrogen and helium, which
only have two.
In the electron dot diagram of water shown at the
right, shows a completed molecule.  If you
remember that oxygen has six electrons and
hydrogen has one.  You can see that when they
are combined they fill all of the outer shells of all
of the atoms.
Chapter 8 - Compounds and Molecules - Electron Dot
Diagrams
Let's look at hydrogen.  Remember that the chemical
symbol for hydrogen is H, and that it has one electron in
it's outer orbit.  When you draw an electron dot diagram
for Hydrogen it would be an H (capital of course) with
one single dot next to it.