why metel+nonmetal makes ionic bond and nonmetal+non metal mkes covaent bond

Question

like H2O WHY IT DOES A COVALENT BOND not ionic?

why doesn't H+ makes an ionic bond with O2- AND GIVE H2O?

IN BOTH CASES WE WILL HAVE THE SAME RESULT SO WHY WE CAN NOT SAY THAT BOTH WAYS ARE CORRECT

Answer 1

Each element has a defined electronegativity with Fluorine having the greatest at 4.00. Electronegativity is the a measure of the atom's pull on the electrons when bonded to another atom. Therefore, elements that are the same and form a molecule, like O2 or N2 or H2, have an electronegativity difference (subtract the electronegativity of one atom from the other atom's electronegativity) of zero. This is a covalent bond. The shared pair of electrons are equally pulled upon from either side so they are right in the middle of the bond (sort of). When there is a large electronegativity difference, as in a group 1 metal like sodium (very low electronegativity) and a non-metal like Cl (very high electronegativity), then the bond is ionic because the electrons are strongly attracted by the chlorine and so are not equally distributed between the atoms in the bond, but are nearer to the chlorine. There is some variation in text books, but usually, if the electronegativity difference is 1.7 or greater, then that defines an ionic bond. Polar covalent bonds have an electronegativity difference between, roughly, .3 and 1.6. An example is water, H2O. The bond is polar because the electrons are more strongly pulled by the oxygen and therefore "reside" on the oxygen side of the bond giving a partial negative charge to the oxygen and a partial positive charge to the hydrogen. This is represented as δ- and δ+, respectively.