How does electronegativity influence the formation of ionic and covalent bonds in molecules?

Electronegativity measures how strongly an atom pulls on shared electrons; it is a key factor in deciding whether two atoms will share or transfer electrons. When the difference in electronegativity between two atoms is large (typically above about 1. 7), the more electronegative atom pulls the shared electrons so strongly that it essentially takes an electron from the less electronegative atom, creating ions and an ionic bond. If the difference is small, the atoms share electrons more equally, forming a covalent bond. For example, sodium (low electronegativity) and chlorine (high electronegativity) give Na⁺ and Cl⁻ ions and form NaCl, whereas hydrogen atoms, with similar electronegativities, share electrons to form H₂.