Atomic Solar System

Just like the solar system has the Sun at the center and Planets orbiting around it, so the atom has a nucleus of protons and neutrons circled by orbiting electrons. In the case of the atom, however, the electron orbits are not nice clear paths but shells or clouds where the electrons can exist. Some clouds are spherical and some are more complex. Some hold only two electrons and some as many as 14. They also can overlap.

The first three periods of the periodic table represent the first three orbits or electron shells. The first period is quite simple. It contains one level and is a spherical shape filled with a maximum of just two electrons. This is labeled as the 1s level. The second period has two levels, the 2s and the 2p. The 2s also has two electrons but the 2p can hold up to six electrons. The third period also has two levels similar to the second period, the 3s and the 3p. They also hold two and six electrons respectively. Thus the largest element in the first three periods has 18 electrons and 18 protons for an atomic number of 18. This is the noble gas Argon.

In the fourth period it begins to get more complicated. The fourth period also has two levels, a 4s and a 4p, with two and six electrons but after the 4s level is filled, then a 3d electron level starts to fill with up to 10 electrons. Since most of the elements we will look at as we move forward fall into the first four periods, this should be enough to give a picture of the layout of the atomic solar system. Here is a simple drawing of the levels and the electrons in each, without going into the complexities of their size, shape and order. The filling of the electron shells influences the type and number of chemical bonds an element may make with other elements.