Which of the following values best classifies a bond between 2 atoms as being ionic?
a. an electronegativity difference of greater than 1.7 between the atoms
b. an electronegativity difference of greater than 2.7 between the atoms
c. an electronegativity difference of less than 1.7 between the atoms
d. an electronegativity difference of less than 2.7 between the atoms

Answer is: A.An electronegativity difference of greater than 1.7 between the atoms.

Electronegativity (χ) is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

Atoms with higher electronegativity attracts more electrons towards it, electrons are closer to that atom.

For example, in ionic salt sodium fluoride (NaF), fluorine has electronegativity approximately χ = 4 and sodium χ = 1 (Δχ = 4 - 1; Δχ = 3), fluorine attracts electron and it has negative charge and sodium has positive charge.