To keep an atom electrically stable, it has the same number of negatively charged electrons in orbit around the nucleus as there are positively charged protons in the nucleus. In situations where there are either more or less electrons in orbit than there are protons in the nucleus, the atom is called an ion. This happens in static electricity and in some chemical solutions.
Electrons are arranged in shells or orbits around the nucleus.
There is a definite arrangement of the electrons in these shells and a maximum number of electrons possible in each shell.
Shell or Orbit Number 1 2 3 4 5
Maximum Number of Electrons 2 8 18 32 50
The most electrons possible in the first shell are 2. After the first shell is filled, the second shell starts filling up, according to the number of positive charges in the nucleus. The most allowed in the second shell is 8 electrons. Then the third shell starts to fill.
Electron shells for a Sodium atom
(atomic number 11, with 11 electrons)
Filling order complicated
After the second orbit or shell is filled, things start to get complicated. The third shell fills until it gets to 8, and then the fourth shell starts adding electrons until it too has 8 electrons. Then the third shell fills until it gets to 18.
Outer shell basis of Chemistry
The number of electrons in each shell can be seen by using the Periodic Table, which is a lesson in Chemistry. In fact, the basis of chemical combinations depends on the number of electrons in the outer orbit or shell.
Electrons have potential energy, depending on their shell or orbit. Energy levels are assigned to each orbit. There are some situations when an electron will jump from one orbit—or energy level—to another. When that happens, the electron gives off electromagnetic energy of one wavelength or color of light.
Since each element has its own electron shell or energy level configuration, it also has its own set of colors for the different possible electron orbit jumps. This fact is used in identifying elements that are giving off light.
The solar system model of the atom is a good way to describe an atom. The nucleus is at the center of the atom and consists of protons and neutrons. There are normally just as many electrons as protons in an atom. The electrons are distributed in shells around the nucleus, according to certain rules. The outer shell is the basis for Chemistry.