Intramolecular interactions, such as covalent bonding and ionic bonding, and intermolecular interactions, such as London dispersion forces and hydrogen bonding, affect the chemical bonding and molecular geometry of substances. These interactions result from attractive and repulsive electrostatic interactions between electric charges. The physical and chemical properties of materials depend on these forces. In intramolecular and ionic interactions, the electronegativity of the involved atoms plays an important role. Two atoms with identical electronegativities can share electrons equally and form nonpolar covalent bonds, two atoms with different electronegativities can share electrons unequally and form polar covalent bonds, and two atoms with greatly differing electronegativities can transfer electrons, forming ionic bonds. Lewis structures allow for modeling covalent bonds and can predict how molecules form. Intermolecular forces are attractions between atoms, ions, or molecules that form matter. Intermolecular forces can occur between molecules with permanent dipole moments, two polar molecules, or an ion and a polar molecule (ion-dipole). Intermolecular forces can also occur between nonpolar molecules.
At A Glance
Chemical bonds form because of electrostatic interactions between protons and electrons. A chemical bond is stable if the total energy of the bonded atoms is less than the total energy of free atoms.
Ionic bonds form between atoms with large differences in electrostatic forces of oppositely charged ions.
Covalent bonds form between atoms with similar electronegativity values. Electrons are shared between atoms in a covalent bond.
- When covalent bonds form between atoms with different electronegativities, the bonding electrons are shared unequally, forming a polar bond.
Lewis structures model covalent bonds by using element symbols and dots around the symbol to represent valence electrons. Lines represent covalent bonds between atoms.
- Molecules can have more than one valid Lewis structure. Formal charge can be used to determine which representation is likely to be lower in energy. Resonance occurs when two or more Lewis structures have equivalent formal charges.
Dipoles carry an unequal charge distribution and can interact with other dipoles or ions. Hydrogen bonding is a special case of dipole-dipole interaction.
- Nonpolar molecules have intermolecular interactions called London dispersion forces. London dispersion forces increase with molecule size.