To draw a Bohr model of an atom, first find the number of protons, neutrons and electrons in the atom from its atomic weight and atomic number. After that, place the neutrons and the protons in the nucleus, and draw the electrons in their designated shells.
- Find the number of electrons, protons and neutrons
From the periodic table, find the element, and identify its atomic number and atomic weight. The atomic number of an element is shown on top of the symbol of the element, and the atomic weight is shown in the bottom. The atomic number of the element is equal to the number of electrons and protons in the element. The number of neutrons is attained by subtracting the atomic number from the atomic weight. For example, carbon has an atomic number of 6 and an atomic weight of 12. So a carbon atom has six electrons, six protons, and six neutrons.
- Draw the nucleus
Draw the nucleus of the atom. Since the nucleus has a number of subatomic particles, it is often impossible to show all the particles in the drawing. Instead, draw a simple circular figure, and identify it as the nucleus. Then, write down the number of protons and neutrons in the nucleus.
- Draw the electrons
In a Bohr model, electrons are housed in shells, and these shells are drawn as circles with the nucleus in their center. Each shell can house up to a fixed number of electrons. The first shell can hold two electrons, the second one can hold eight electrons, the third one can hold 18 and so on. Each shell is drawn with an increasing radius so that the first shell has the smallest radius. Draw the first shell and draw two electrons on the shell. If there are more than two electrons in the atom, then draw the second shell and place the remaining electrons on it. If the second shell reaches its capacity and there are still electrons left, draw the third shell, and continue this process until all electrons are drawn. For example, a Bohr model of carbon has two electrons on the first shell and four electrons on the second.