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Hydrogen Bonding – Definition, Effects, Types, Properties

  • Last Updated : 02 Dec, 2021

Hydrogen bonding is an electrostatic dipole-to-dipole contact between molecules that shares certain covalent bonding characteristics. Hydrogen bonding is strong and directed, resulting in shorter interatomic distances and a small number of interaction partners. Its strength per mole of hydrogen bonds ranges from 4 kJ to 50 kJ. In hydrogen bonding, the interaction between a lone pair of an electron-rich donor atom, particularly second-row elements such as Nitrogen, Oxygen, and Fluorine, and the antibonding molecular orbital of a bond between hydrogen and a more electronegative atom or group is referred to as partial intermolecular bonding. 

While hydrogen bonds contribute both electrostatically and covalently, the extent to which they do so is still debated. The current research suggests that the predominant contribution is covalent.

Hydrogen Bonding

Hydrogen bonding is the development of hydrogen bonds, which are a type of attractive intermolecular force caused by the dipole-dipole interaction between a hydrogen atom bound to a strongly electronegative atom and another very electronegative atom nearby. Hydrogen is covalently bound to the more electronegative oxygen atom in water molecules (H2O). 

As a result of dipole-dipole interactions between the hydrogen atom of one water molecule and the oxygen atom of another H2O molecule, hydrogen bonding occurs in water molecules.

The bond pair of electrons in the O-H bond is quite close to the oxygen nucleus in this case (due to the large difference in the electronegativities of oxygen and hydrogen). As a result, the hydrogen atom generates a partial positive charge (+) whereas the oxygen atom develops a partial negative charge (-). 

The electrostatic interaction between the hydrogen atom of one water molecule (with + charge) and the oxygen atom of another water molecule (with – charge) can now cause hydrogen bonding. As a result, hydrogen bonds are a unique type of intermolecular attractive force that only occurs when hydrogen atoms are bound to a highly electronegative atom. In comparison to typical dipole-dipole and dispersion forces, hydrogen bonds are primarily strong. They are, however, weaker than actual covalent or ionic connections.

Conditions required for Hydrogen Bonding

  • A highly electronegative atom must be coupled to the hydrogen atom in the molecule. The polarisation of a molecule is proportional to its electronegativity.
  • The electronegative atom should be modest in size. The greater the electrostatic attraction, the smaller the size.

Effects of Hydrogen Bonding on Elements

  1. Dissociation: HF dissociates in water and sends off the difluoride ion instead of the fluoride ion. In HF, this is due to hydrogen bonding. HCl, HBr, and HI molecules do not form hydrogen bonds. This explains why chemicals like KHCl2, KHBr2, and KHI2 don’t exist.
  2. Association: Because of hydrogen bonding, carboxylic acid molecules exist as dimers. Such compounds have molecular weights that are twice as large as those calculated from their simple formula.

Examples of Hydrogen Bonding

  • Water – A highly electronegative oxygen atom is connected to a hydrogen atom in the water molecule. The shared pair of electrons are attracted to the oxygen atoms more, and this end of the molecule becomes negative, while the hydrogen atoms become positive.

  • Hydrogen Floride – The strongest hydrogen bond is formed by fluorine, which has the highest electronegativity.

  • Ammonia – It comprises nitrogen atoms that are strongly electronegative and are coupled to hydrogen atoms.

  • Alcohol and Carboxylic Acid 

Strength of Hydrogen Bond: The hydrogen bond is a relatively weak one. Hydrogen bonds have a strength that is halfway between weak van der Waals forces and strong covalent bonds. The attraction of the shared pair of electrons, and hence the atom’s electronegativity, determines the hydrogen bond’s dissociation energy.

Properties of Hydrogen Bonding

  1. Volatility – The boiling point of compounds incorporating hydrogen bonding between distinct molecules is greater, hence they are less volatile.
  2. Solubility – Because of the hydrogen bonding that can occur between water and the alcohol molecule, lower alcohols are soluble in water.
  3. The lower density of ice than water – In the case of solid ice, hydrogen bonding causes water molecules to form a cage-like structure. In fact, each water molecule is tetrahedrally connected to four other water molecules. In the solid state, the molecules are not as tightly packed as they are in the liquid state. This case-like structure collapses as ice melts, bringing the molecules closer together. As a result, the volume of water reduces while the density increases for the same quantity of water. As a result, at 273 K, ice has a lower density than water. Ice floats because of this.
  4. Viscosity and surface tension – Hydrogen bonding is found in compounds that have an associated molecule. As a result, their flow becomes more complicated. They have high surface tension and have a higher viscosity.

Why do hydrogen-bonded compounds have high melting and boiling points?

The melting and boiling temperatures of hydrogen-bonded compounds are unusually high. The elevated melting and boiling points of hydrogen-bonded compounds are attributable to the additional energy required to break these bonds.

  • At room temperature, H2O is a liquid, whereas H2S, H2Se, and H2Te are all gases. Hydrogen bonding produces links in the water molecules, resulting in water having a higher boiling point than the other chemicals.
  • Because there is hydrogen bonding in NH3, but not in PH3, ammonia has a higher boiling point than PH3.
  • The presence of hydrogen bonding accounts for hydrogen fluoride’s particularly high boiling point among the halogen acids.
  • Because ethanol contains hydrogen bonds, it has a higher boiling point than diethyl ether.

Types of Hydrogen Bonding

There are two types of H bonds, which are labelled as follows:

  1. Intermolecular Hydrogen Bonding – Intermolecular hydrogen bonding occurs when hydrogen bonds are formed between molecules of the same or distinct substances. Hydrogen bonding in water, alcohol, and ammonia, for example.
  2. Intramolecular Hydrogen Bonding – Intramolecular hydrogen bonding refers to hydrogen bonding that occurs within a single molecule. It occurs in compounds with two groups, one of which has a hydrogen atom linked to an electronegative atom and the other of which has a highly electronegative atom linked to a less electronegative atom of the other group. The link is created between the more electronegative atoms of one group and the hydrogen atoms of the other group.

Sample Questions

Question 1: State Octet Rule.

Answer:

Atoms are most stable when their valence shells are filled with eight electrons, according to the octet rule. It is based on the observation that the atoms of the major group elements have a proclivity for chemical bonding in such a way that each atom in the resulting molecule has eight electrons in the valence shell. Only the core group elements are subject to the octet rule.

Question 2: What are the factors that affect the formation of Ionic Bond?

Answer: 

Factors affecting the formation of Ionic Bond are:- 

  • Ionization Enthalpy
  • Electron Gain Enthalpy
  • Lattice Energy

Question 3: List any three characteristics of Ionic Compounds.

Answer:

Characteristics of Ionic Compounds are as follows:-

  1. The melting and boiling points of ionic compounds are usually quite high. This is due to the strong electrostatic forces that hold ions together in ionic compounds.
  2. Ionic compounds are frequently found in solid form.
  3. Ionic compound solutions are excellent electrical conductors. In their molten condition, they are also good conductors of electricity.

Question 4: What is Hydrogen Bonding?

Answer:

When a hydrogen atom is coupled to a highly electronegative atom, the shared pair of electrons are attracted more by this atom, and the molecules’ negative end becomes slightly negative while the positive end becomes slightly positive.The negative end of one molecule attracts the positive end of the other, resulting in the formation of a weak bond. This connection is referred to as Hydrogen Bonding.

Question 5: What are the conditions required for Hydrogen Bonding?

Answer:

Conditions required for Hydrogen Bonding are:

  • A highly electronegative atom must be coupled to the hydrogen atom in the molecule. The polarisation of a molecule is proportional to its electronegativity.
  • The electronegative atom should be modest in size. The greater the electrostatic attraction, the smaller the size.

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