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.;

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.

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