Question

Why sodium has strong tendency to form electrovalent bond?

Answer 1

Usually elements with the largest or smallest electronegativity, like fluorine and cesium.

Ionic compounds when two elements with a large electronegativity bond. So the property of a bond determines more on the electronegativity difference than the EN of a single elements. Nevertheless, elements with very low or very high electronegativity are likely to form an ionic bond. Fluorine, oxygen, nitrogen and chlorine have EN. Cesium, barium and potassium have low EN.