Download 3.4 – The Planetary Model of the Atom

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The Model of the Atom
Model of the atom
The information on which we base our models of
atoms has been obtained from research
performed by many scientists. They have
developed many models, some which have
been disproved, and some which are still being
developed. The model we teach is not the only
one, and will be expanded upon in future
Planetary Model of the Atom
This model of the atom describes the atomic structure as
• Protons and neutrons make up the nucleus of the
• The nucleus is at the centre of the atom.
• Electrons move in orbits (circular pathways) around
the nucleus (like planets orbit the sun).
• The electrons fill these orbits in a specific pattern.
Models of Hydrogen and Helium atoms
Electron Configuration
Electrons fill the orbits around the nucleus of an atom in
specific patterns.
• The first orbit (closest to the nucleus) holds only 2
• The electrons fill the second orbit only when the first
orbit is filled.
• The second orbit is drawn as a concentric circle
outside the first orbit. It holds up to 8 electrons.
• The third orbit (again filled only when the inner 2
orbits are full) holds up to 8 electrons as well.
Bohr-Rutherford Model of the Atom
The planetary model of the atom is also known
as the Bohr-Rutherford model of the atom. It
is named after the 2 scientists who worked to
discover information that helped us to
understand the structure of the atom.
Contributors to the BohrRutherford Model of the Atom
How to Draw a Bohr-Rutherford
Calculate the numbers of protons, neutrons and
electrons from the atomic and mass numbers of an
Draw a nucleus for your atom (draw as a circle). Put
your proton and neutron numbers in the nucleus.
Draw the first orbit as a concentric circle around the
nucleus. Put up to 2 electrons in this orbit. If there
are more than 2 electrons in your atom, place 2 here
and draw a second orbit.
How to Draw a Bohr-Rutherford
Place up to 8 electrons in the second orbit. If
there are more than 10 electrons in your atom
(2 in orbit #1, and 8 in orbit #2), draw a third
Place up to 8 electrons in the third orbit. If
there are more than 18 electrons in your atom
(2 in orbit #1, 8 in orbit #2, and 8 in orbit #3),
draw a fourth orbit.
How to Draw a Bohr-Rutherford
6. If you are adding electrons in the fourth orbit,
only 2 may be added. This orbit can hold
many more, but the electron configuration does
not follow the rules of the Bohr-Rutherford
model if more than 2 electrons are added.
Bohr-Rutherford Diagram of Boron
Boron – atomic # 5
atomic mass 11
# p+= 5
# e- = 5
# no = 11-5 =6