The Effects of Electronegativity

(1) What principles dictate the relationships between molecules? There are many factors at work, but these interactions also depend indirectly on a principle known as electronegativity. Although this is an atomic property, it generates molecular (2) forces, that cause many of the phenomena we observe every day. (3) Electronegativity, the measure of an atom’s affinity for electrons, generally determines the type of bond present between two atoms. A single bond between atoms consists of two electrons. If the two atoms have similar electronegativities, they share the two electrons equally and form a nonpolar covalent bond. If two atoms have significantly differing values of electronegativity, there are two possible bond types: polar covalent and ionic. While other factors also (4) corrupt the determination of bond type, a difference in electronegativity between the values of 0.5 and 1.6 usually (5) result in a polar covalent bond, while a difference of more than 2.0 usually results in an ionic bond. In a polar covalent bond, the two bonding electrons are shared (6) unequally, in an ionic bond: both electrons are completely transferred to the more electronegative atom. For example, the bond between oxygen (O) and hydrogen (H) is classified as a polar covalent bond, because (7) The presence of surface tension in water is just one result of hydrogen bonding. From digestion to DNA structure, this molecular force is integral (8) with many life-sustaining processes. If atoms did not have different values of electronegativity, hydrogen bonding would be impossible—and life as we know it could not exist. they share the two bonding electrons unequally. This polar bond type is partially caused by the difference in electronegativities: (9) hydrogen has an electronegativity of 2.20, while oxygen has an electronegativity of 3.44.

When the electronegativity of the hydrogen is subtracted from the electronegativity of the oxygen, the difference is 1.24. When a hydrogen atom is bonded to nitrogen, oxygen, or fluorine, this particular polar covalent bond makes that a new type of interaction possible: hydrogen bonding. For instance, a water molecule consists of an oxygen atom bonded to two hydrogen atoms. The unequal sharing of electrons causes a distribution of partial charges on the molecule. The oxygen of one water molecule monopolizes the bonding electrons and acquires a partial negative (10) charge; as a result, this oxygen atom is attracted to the partially positive hydrogen atoms of another water molecule. This electrostatic attraction, (11) which is an attraction referred to as intermolecular hydrogen bonding, contributes to the surface tension that sustains the weight of water striders and some other insects.