In terms of the periodic table, is there an abrupt or gradual change between ionic and covalent bonds?

(a) An abrupt change occurs across the metalloids.

(b) Actually, any element of the periodic table can form a covalent bond.

(c) There is a gradual change; the farther apart the elements, the more ionic.

(d) Whether an element forms an ionic or a covalent bond depends on nuclear charge, not on the relative positions in the periodic table.