Atoms don't "desire" electrons in the way that humans do. It's more accurate to say that atoms are driven by a tendency to achieve stability in their electron configuration. This stability is achieved by having a full outer shell of electrons, which is the most energetically favorable state.

Here's a breakdown:

* The Octet Rule: Most atoms strive to have eight electrons in their outermost shell (the valence shell). This is known as the octet rule.

* Exceptions: Some elements, especially those in the first and second periods, are stable with just two electrons in their outer shell (like helium).

* Gaining, Losing, or Sharing: To achieve stability, atoms might:

* Gain electrons: Nonmetals tend to gain electrons to fill their outer shell.

* Lose electrons: Metals tend to lose electrons to expose a full inner shell.

* Share electrons: This is what happens in covalent bonding, where atoms share electrons to achieve a full outer shell.

Example:

* Chlorine has 7 electrons in its outer shell. It needs one more electron to have a full outer shell of 8.

* Sodium has 1 electron in its outer shell. It can easily lose this electron to have a full outer shell of 8 in the next inner shell.

In summary, the number of electrons an atom "desires" is based on the number needed to fill its outer shell and achieve stability. This is what drives chemical reactions and the formation of molecules.