Answer:
Attraction betwenen the atoms.
Step-by-step explanation:
The force of attraction between two atoms creates a lasting chemical bond between them. This force can be as a result of the loss and gain of electrons between two atoms as in the case of ionic bonds. In ionic bonds, an electrostatic force of attraction between oppositely charged ions leads to the bond formation.
In some other atoms, electrons can be shared between two atoms. The atoms can both donate the shared electrons or one specie donates the electron. This is the case of covalent bonds.