The correct answer is:
electronegativity
Step-by-step explanation:
Electronegativity is a model of an atom's strength to attract the shared electrons of a covalent bond to itself. If atoms bonded together have the same electronegativity, the allotted electrons will be moderately shared. If the electrons of a bond are higher attracted to one of the atoms (because it is more electronegative), the electrons will be unevenly shared. If the difference in electronegativity is large enough, the electrons will not be allowed at all; the more electronegative atom will "take" them happening in two ions and an ionic bond.