How do electronegativity differences influence bond character?

Electronegativity differences determine whether a bond is ionic, covalent, or polar covalent.

Electronegativity is a measure of the ability of an atom to attract a bonding pair of electrons. When two atoms form a chemical bond, the atom with the higher electronegativity will have a greater share of the electron density. This difference in electronegativity between the two atoms determines the character of the bond.

If the electronegativity difference is large (greater than 1.7), the bond is ionic. This is because the atom with the higher electronegativity will attract the electrons so strongly that it essentially takes an electron from the other atom, resulting in the formation of ions. For example, in sodium chloride (NaCl), sodium (Na) has an electronegativity of 0.93 and chlorine (Cl) has an electronegativity of 3.16. The difference is 2.23, which is greater than 1.7, so the bond is ionic.

If the electronegativity difference is small (less than 0.5), the bond is covalent. This means that the electrons are shared more or less equally between the two atoms. For instance, in a molecule of chlorine gas (Cl2), both chlorine atoms have the same electronegativity, so the difference is zero. This means the bond is perfectly covalent.

If the electronegativity difference is intermediate (between 0.5 and 1.7), the bond is polar covalent. In a polar covalent bond, the electrons are shared, but not equally. The atom with the higher electronegativity will have a slightly greater share of the electron density, resulting in a partial negative charge (δ-), while the other atom will have a partial positive charge (δ+). An example of this is water (H2O), where the oxygen atom is more electronegative than the hydrogen atoms, resulting in a polar covalent bond.

In summary, the difference in electronegativity between two atoms influences the character of the bond they form. It determines whether the bond is ionic, covalent, or polar covalent, which in turn affects the physical and chemical properties of the substance.