Covalent bond is formed when electrons are shared by the atoms to fulfill their outermost shell.
In colvalent bond atoms shares electron to gain stability because if their outermost shell is not fulfilled then they are unstable.
So to gain stability electrons are shared by atoms in covalent bond , when they share electron their outermost shells are fulfilled and they become stable
Atoms in covalent bonds do combine so as to be stable. As covalent bond consist non metals e.g O2 in this example each atom has vacance of 2 orbitals/ electrons so shairing electrons result their stability
