Chem – Bohr Model and Electron Shells Part 1

What sections should I know before attempting to learn this section?

—> Protons and Electrons


What is the Bohr model of the atom?

The amount and arrangement of electrons around two or more different atoms are the best way to predict how they will interact. This is why electrons are talked about so extensively in chemistry. The most simplistic, yet still correct way to understand how electrons move in atoms is called the Bohr model. The Bohr model is simply a picture of the atom with the protons and neutrons in the middle and the electrons traveling in ever-larger rings around that middle. Some people call this the solar system model because it looks much like our solar system with the sun (nucleus) in the middle and the planets (electrons) running in ever-wider rings around the center. Here is a picture of the Bohr model.


The rings that electrons travel in the Bohr model are referred to as electron shells. The first electron shell is closest to the nucleus and the second shell a little further away. As we get higher and higher in electron shells we get further from the nucleus. From the periodic table, you can model how the electron shells are created. This is a link of the electron shells shown on the periodic table. The picture above of the Bohr model is a representation of an atom with the first three energy shells full of electrons.  It would therefore be representing the neutral atom of Argon (Keep in mind the nucleus is not completely drawn there).


In chemistry classes, two common questions are asked about the electrons shells:

1) How many electron shells does a certain element have?

2) How many electrons are in the last electron shell of a particular element?


We answer the first question in this section and the second question in the next section.


Examples: How many electron shells does each pure element have?  Use the electron shells periodic table.  VIDEO Electron Shells Examples 1.


Li 2
P 3
I 5


PRACTICE PROBLEMS: How many electron shells does each pure element have?  Try using the regular periodic table.  Use the electron shells periodic table if you need to.


Sn 5
Ba 6
Cu 4
N 2



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