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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 courses. Planetary Model of the Atom This model of the atom describes the atomic structure as follows: • Protons and neutrons make up the nucleus of the atom. • 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 electrons. • 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 Ernest Rutherford Niels Bohr How to Draw a Bohr-Rutherford diagram 1. 2. 3. Calculate the numbers of protons, neutrons and electrons from the atomic and mass numbers of an element. 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 diagram 4. 5. 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 orbit. 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 diagram 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