Intermolecular Forces of Attraction

• Intermolecular forces are attractive forces present in between molecules.
• 4 Main Types of IMFA

  1. London dispersion forces
  2. Dipole-dipole forces
  3. Ion-dipole forces
  4. Hydrogen bonding forces
• London dispersion forces and Dipole-dipole forces are collectively known as van der Waals forces of attraction, named after the Dutch scientist Johannes van der Waals.
• Ion-ion interaction is the interaction between two oppositely charged particles.
• In chemistry, charged particles are called ions.
• Cations are positively charged particles, while anions are negatively charged particles.
• Ion-ion interaction is also known as ionic bonds. This type of bond holds together the particles in an ionic compound.
• Ion-dipole interaction results from the electrostatic attraction of a molecule containing a dipole and an ion.
• Ion-dipole interaction is responsible for the dissolution of most ionic solids in polar solvents.
• The strength of ion-dipole interaction depends on the charge density of the ion.
• Charge density is defined as the actual charge distributed over the total volume of the ion.
• Dipole-dipole interactions are attractive forces that are a moderately strong type of IMFA and are present in between polar molecules.
• Dipole-dipole forces are the result of the electrical interactions among dipoles on neighboring molecules.
• Hydrogen bonding is a special kind of dipole-dipole force and one of the strongest types of IMFA.
• Hydrogen bonding is an attractive force that exists when hydrogen is bonded to the most electronegative atoms, namely F, O, or N.
• A hydrogen bond donor is a molecule that provides the hydrogen atom participating in a hydrogen bond
• hydrogen bond acceptor is a molecule that contains the lone pair-bearing electronegative atom.
• London dispersion forces (LDFs) are the weakest type of IMFA and are present in between all electrically neutral molecules ― polar and nonpolar molecules.
• London dispersion forces (LDFs) was named after the German-American physicist Fritz London who initially proposed this intermolecular force of attractions.
• Because the electrons of these molecules are constantly moving, there are times when electrons move to one end, making such end partially negative while the other end becomes partially positive. Hence, the molecule can have an instantaneous dipole.
• There are two types of induced dipole forces — ion-induced and dipole-induced.
• compounds can be classified as ionic or covalent based on the types of bonds present.
• ionic compound is composed of atoms bonded by ionic bonds.
• Ionic bonds involve the transfer of an electron from a metal to a nonmetal.
• The cations and anions in an ionic compound interact via ion-ion interactions.
• The strength of the ion-ion interaction is governed by Coulomb's law.
• Covalent bonds involve the sharing of electrons between two nonmetal atoms.
• Polar covalent compounds are molecules with a net dipole moment. This means that the electrons are not equally shared between the atoms.
• Nonpolar covalent compounds are molecules with zero dipole moment. This means that the electrons in the bonds are shared equally between the atoms.
• Polarizability is the measure of how easy it is to distort the electron distribution of a molecule.