Do atoms have a maximum number of electrons? And therefore a maximum number of bindings?

Answer

Dear Cees,

Short answer: Basically you can add as many electrons to an atom as you want or for which you have the energy available to force an atom to take up electrons. However, this is not a relevant discussion because most such states are quite exotic and short-lived. In the following I will limit myself to states that have a certain stability and lead to particles with a certain lifetime. Second, there is no direct relationship between the number of electrons and the number of bonds an atom forms.

The number of electrons an atom has in its neutral state is always equal to the number of protons in the nucleus and is indicated by its atomic number, eg oxygen nr. 8 has 8 electrons and 8 protons in its neutral state. In compounds that number of electrons can increase or decrease depending on which number gives the most stable state for this atom, eg oxygen usually has two extra electrons in its compounds such that it usually shows a twofold negative charge and possibly two bonds with other atoms. You can in principle add more electrons, but that does not lead to a stable state. Another example is Calcium, in its most stable state this atom has a twofold positive charge. Like most metals, Calcium will prefer the loss of electrons to arrive at a steady state. This indicates that the state in which an atom exists, and how many bonds it has, cannot be deduced directly from the absolute number of electrons. Actually, as stated before, there is no connection.

The relationship between bonds and electrons of an atom is a bit more complicated and linked with the organization of electrons around an atom. The structure or electron configuration consists of “shells” and “subshells” that can hold a max number of electrons. This max number eg for the “shells” is 2x nxn where n represents the number of the shell starting from the core. eg. 2nd shell contains max 8 electrons, 1st shell contains max 2 electrons. These shells can be filled in thought with electrons leaving from the first. If we do this for oxygen, we can place 6 of the eight electrons in the second shell, because 2 are already placed in the first shell before we can start the second shell. Now it is indicated at the top that oxygen strives in one way or another to take in two extra electrons. This will lead to a completely filled 2nd shell, viz. 8 electrons. Apparently that results in an energetically very favorable state and that is a fairly common observation. Atoms will form bonds in such a way that they realize a completely filled shell and preferably a completely filled shell with eight electrons. This is called the octet rule.

If you want to know more about this, I recommend that you consult a basic chemistry textbook from secondary education or visit a few sites on the internet:

eg http://nl.wikipedia.org/wiki/Electronenconfiguration