Types of Hydrogen Bonding

Types of Hydrogen Bonding

• Two main types of hydrogen bonding are observed: intermolecular and intramolecular.
• Intermolecular hydrogen bonding occurs between different polar molecules (same or different substances). Examples include water, hydrogen fluoride, and ammonia.
• Intramolecular hydrogen bonding occurs between atoms of the same molecule, typically forming a ring structure. Examples include ortho-fluorophenol, ortho-nitroaniline, and ortho-hydroxybenzaldehyde.
• Hydrogen bonding is a special dipole-dipole type of interaction.
• Strength depends on the electronegativity of the atom to which the hydrogen is bonded, with highly electronegative atoms (F, O, N) showing stronger hydrogen bonds.

Intermolecular Hydrogen Bonding

• Water (H₂O) is a key example.
• Hydrogen bonds form between the highly electronegative oxygen atom of one water molecule and the hydrogen atom of another.
• These bonds influence the physical properties of water, including its high boiling point.

Intramolecular Hydrogen Bonding

• Hydrogen bonding within the same molecule (intramolecular).
• The bonding causes a ring structure to form.
• Illustrated for example with para-nitrophenol.
• Intramolecular hydrogen bonds are often found in compounds with specific molecular structures leading to unique properties.

Key Points about Hydrogen Bonding

• Hydrogen bonding is crucial for the properties of many substances.
• It plays a significant role in biological systems, influencing protein folding, DNA structure, and water's unique characteristics.
• The strength of a hydrogen bond varies, depending on factors like the electronegativity difference between the atoms and the molecular geometry.

Lewis Symbols (Electron Dot Structures)

• G.N. Lewis used simple notations (Lewis symbols/electron dot symbols) to represent valence electrons.
• The element's symbol represents the atom, excluding valence electrons.
• Dots and crosses around the symbol represent valence electrons.

Covalent Bond and Hydrogen Bond

• Covalent Bonds: Formed by sharing electrons between atoms which usually are non-metals. (Formed between atoms of similar or different electronegativities).
  • Polar Covalent Bonds: Electron sharing is unequal, leading to a partial positive charge on one atom and a partial negative charge on another.
  • Non-polar Covalent Bonds: Electron sharing is equal.
  • Co-ordinate Covalent Bonds: One atom provides both the shared electrons.
• Hydrogen Bond: A weak electrostatic bond formed between a slightly positive hydrogen atom and a highly electronegative atom (F, O, N).

Properties of Covalent Compounds

• General Characteristics: Often gases or liquids at room temperature, low melting/boiling points, poor conductors of electricity, and limited solubility in water.
• Exceptions: Diamond (a hard solid). Some substances are good conductors when dissolved in water. (Graphite)
• Reactions: Generally slow due to electron rearrangement needed for bond breaking and formation.

Factors Favouring Ionic Bond Formation

• Transfer of electrons to achieve stable octet/duplet configurations.
• Low ionization energy (cation, loses electrons).
• High electron affinity (anion, gains electrons).
• Large differences in electronegativity.

Properties of Ionic Compounds

• General Characteristics: Solid crystalline structures at room temperature, high melting/boiling points, high density, poor conductors in solid state but excellent conductors in molten or aqueous solutions.
• Solubility: Often soluble in polar solvents like water, insoluble in non-polar solvents.