Answer 1:
The Periodic Table of elements can tell you a lot
about the elements. Oxygen with the symbol
O has
the atomic number 8 which means it is the 8th
element in the table. The number eight also means
that oxygen has eight protons in the nucleus.
The number of protons and the number of
electrons are always the same in an element that
is neutral and has no charge. Therefore oxygen has
8 electrons.
The number of neutrons
normally varies and can be calculated from the
atomic weight. If you click on the symbol in the
periodic table at this web
site
here
You
will find that the atomic weight of oxygen is
about 16. Since the weight of the protons and
neutrons is about 1 (the electrons weigh almost
nothing compared to protons and neutrons) and we
know we have 8 protons in the nucleus, we can
calculate the number of neutrons by subtracting 8
from 16 (16 - 8) which equals 8.
The oxygen atom
has therefore 8 neutrons, 8 protons and 8
electrons.
The number of valence electrons
is equal with the group number. Since oxygen is in
group 6 it means that it has 6 valence
electrons.
Check out the periodic table
from the web site above. You will see that the
number of protons and electrons are easy to
determine. (The number in the upper right corner)
The number of neutrons are a bit trickier since
most of the elements have isotopes. | 
