What is the goal number of electrons to be achieved in the outermost energy shell for a chemical bond to occur?

The answer is; 8

This is also referred to as the octet rule. Inert elements tend to have an 8 election configuration in their outermost shell while other elements react to achieve this electron configuration. This is determined by their  position in the periodic table. However, there are exceptions; Helium has a 2 stable electron configuration in the outermost shell while transition metals have stable 18-electron configuration.;

the form of energy changes and the total energy increases0l