Si el sodio posee una electronegatividad de 2,1 y el cloro de 3,5 se espera que formen:

See the explanation below, please.

Explanation:

Electronegativity is defined as the amount of force through the atom that attracts electrons in a bond. That is, an element with a high electronegativity attracts electrons with great force (chlorine), and those with low electronegativity with less force (sodium). In this case, in the sodium chloride ionic compound (NaCl), the electrons will be attracted to the chloride.