Atom Models

After reading this section you will be able to do the following:

  • Describe the basic structure of an atom.
  • Explain what holds an atom together.

Atom Composition

As previously mentioned, an atom is the smallest particle of any element that still retains the characteristics of that element. However, atoms consist of even smaller particles - subatomic particles. Atoms have a central, dense nucleus of protons and neutrons that is surrounded by one or more electroncs (lightweight negatively charged subatomic particles). An atom is held together by forces of attraction between the electrons and the protons. The neutrons help to hold the protons together. Protons and neutrons are believed to be made up of even smaller particles called quarks. We will limit our discussions to protons, neutrons and electrons.

In the Bohr model the electron orbits the atomic nucleus (proton and neutron). The Bohr model is oversimplified and electrons do not really orbit like planets around the sun.

Niels Bohr was a Danish scientist who introduced the model of an atom in 1913. Bohr's model consists of a central nucleus surrounded by  electrons that are orbiting the nucleus in a cloud, like is shown in the figures above and below. These electrons are spinning so fast around the nucleus of the atom that they would be just a blur if we could see particles that small. In our pictures and exercises the electron appears to orbit in the same path around the nucleus much like the planets orbit the Sun. But, please be aware that electrons do not really orbit in the same path. The electrons are closer to being rotating diffuse clouds.


This image shows multiple electrons orbiting a nucleus of protons and neutrons: Bohr's model of an atom.

Review

  1. Atoms are composed of protons, neutrons, and electrons.
  2. The forces of attraction between the electrons and the protons hold an atom together.