Intermolecular Forces are the forces that exist between the molecules of a compound. Intermolecular forces are much weaker than intramolecular forces. The forces help to determine the physical properties of a molecule such as melting point, boiling point, density, etc. The intermolecular forces are established due to the force of attraction existing between the charged particles. Hence, intermolecular forces are electrostatic in nature.
Types of Intermolecular Forces
1. Dipole-Dipole Interaction
Dipole-dipole interaction exists between the differently charged particles of a molecule. In other words, the interconnection that lies within a part of a molecule that is partially negatively charged and another part of a molecule that is partially positively charged is called a dipole-dipole interaction. The only requirement of such interaction force to exist is that the elements must be charged with different polarity charges. These are the strongest intermolecular forces of attraction existing in nature. For example, a dipole-dipole force of attraction helps to bind a hydrogen atom with a chlorine atom to form a hydrochloride molecule. A similar type of interaction is present between an ion and a dipole, known as an ion-dipole interaction.
2. Hydrogen Bonding
Hydrogen bonding is a special case of dipole-dipole interaction. It specifically occurs when a hydrogen atom is bonded to a nitrogen, oxygen, or fluorine atom. Hydrogen consists of a partially positive charge, whereas oxygen, fluorine, or nitrogen are partially negatively charged. This difference in the polarity of charges on the atoms establishes a force of attraction, which is responsible for a hydrogen bond to exist between them. It is highly difficult to break hydrogen bonds and therefore requires a lot of energy. Some examples of a hydrogen bond are water (H2O) and hydrogen fluoride (HF). This is the reason why the melting and boiling point of water is considerably high. The hydrogen bond is the strongest of dipole-dipole interactions.
3. London Dispersion Forces
London dispersion forces occur between temporary or induced dipoles. It is a temporary force of attraction that exists between the electrons of two adjacent atoms. These are the weakest of all the intermolecular forces. London dispersion force is proportional to the number of electrons contained by a molecule. They are a part of van der Waals forces. The more be the London dispersion force, the more will be the boiling point of the compound. These forces do not require a huge amount of energy to break down.
Deoxyribonucleic Acid or DNA is a chemical compound that stores all the genetic information of a living being. Hydrogen bonding is responsible for the existence of a DNA molecule. A strong force of interaction existing between the four parts, namely adenine, guanine, cytosine, and thymine that leads to the formation of DNA.
Proteins are long chain polymers made up of amino acids. These long chains are known as polypeptides. They play a key role in the life of all living beings. The primary structure of proteins is formed by the covalent bond existing between the amino acid molecules. The secondary structure is made up of the hydrogen bonding present between the different sections of the protein chain. The process with which a protein compound folds and forms its tertiary structure involves intermolecular forces to establish a strong bond.
The movement of water through the xylem and other parts of a plant makes use of hydrogen bonding. Plants containing tiny and rigid tubes that are made up of cellulose. A strong adhesive force exists between water and the cellulose walls. This force supports the capillary action that is used to supply nutrients and fluids to the stem, trunk, and other parts of a plant. Hydrogen bonding is responsible for the upward movement of water molecules through the xylem as continuous columns.
4. Soap and Detergents
The soap bubbles are made up of soap molecules and water molecules. Water is a polar molecule, whereas a soap bubble has a polar and non-polar end. The polar ends of both the molecules get attracted to each other, which helps in the establishment of an intermolecular force. This intermolecular interaction is accountable to hold the bubbles together.
Water is composed of hydrogen and oxygen atoms. The atoms are bonded to each other using the hydrogen bond. A hydrogen bond is a special form of the dipole-dipole bond that exists between partially positive hydrogen and partially negative oxygen of another molecule. The intermolecular force existing within the compounds helps the water molecules to stick to each other. The hydrogen bond is the strongest intermolecular bond, which is why it is difficult to separate the molecules of water from each other. The same reason explains why water has a high boiling point.