The number of protons in an atom is its atomic
number
The Structure
The Neutrons and Protons are
found in the nucleus which is at the
centre of the diagram.
Electrons are around the nucleus in shells.
Depending on the shell, it depends how many electrons fit onto it.
The first shell around the
nucleus can hold up yo 2
electrons, the second and third
can hold up to 8
The number of protons is
always the same as the
number of electrons
The number of electrons
on the outer most shell
shows what group the
element is in
For example, in this diagram,
there are 6 electrons on the
outer ring, this means it must
be in group 6 on the periodic
table.
If you count up
the number of
electrons on the
diagram, it
equals the
atomic number
of the element
Example
This atom diagram has the electron number - 2,8,1
It has 3 shells and the last shell
has 1 electron on it, this means it
is in group 1 on the periodic table
The total number of electrons is 11. This
means the element must be Sodium.
Theories
Dalton
He came up with some theories in the
1800's. He did many tests and came to
these main conclusions
All matter is made of
atoms
Atoms can't be made any
smaller
Compounds are made when 2
or more atoms are joined
together
JJ
Thompson
He discovered the electron in
1897. He found out that atoms
could be broken into smaller
peices.
Rutherford
In 1911 Ernest Rutherford used
experiments to show that an atom
contains a central nucleus. This
supported the fact that an atom can
be broken into smaller pieces.
Bohr
Neil further developed
Rutherford idea of the
atomic model. He found
out that electrons orbit
the nucleus in shells.