Chemical Bonding | General Awareness for SSC CGL PDF Download

Introduction

Constituents of different elements, except for noble gases, do not have a complete octet of electrons, prompting them to combine with other atoms through chemical bonds to achieve stability. This process is called chemical bonding and is determined by the valency of the atoms.

Valency

• Valency is the capacity of an atom or element to form chemical bonds.
• For metals, valency equals the number of valence electrons in the atom.
• For non-metals, valency is determined by subtracting the number of valence electrons from eight.

Ions

An ion is an electrically charged species. Positively charged ions are called cations, while negatively charged ions are called anions. Cations have fewer electrons than their corresponding atoms (e.g., Na⁺, H⁺, Mg²⁺), while anions have more electrons (e.g., F⁻, Cl⁻, O²⁻).

Types of Chemical Bonds

Chemical bonds are classified based on the mode of electron transfer or sharing and the forces of attraction involved:

Electrovalent or Ionic Bond

• Formed by the transfer of electrons from one atom to another, resulting in electrovalent or ionic compounds, typically formed between metals and non-metals.
• Electrovalent compounds are made of charged atoms or groups of atoms and are usually crystalline solids.
• They have high melting and boiling points, conduct electricity when dissolved in water, are soluble in water, and insoluble in organic solvents like alcohol.
• A bond with an electronegativity difference of 1.7 between two atoms is 50% ionic.

Covalent Bond

• Formed by the sharing of electrons between two atoms, resulting in covalent compounds.
• These bonds can be single, double, or triple, depending on the number of shared electron pairs.
• Covalent compounds are usually liquids or gases with low melting and boiling points, do not conduct electricity, and are insoluble in water but soluble in organic solvents.

Coordinate or Dative Covalent Bond

• Formed by the one-sided sharing of one pair of electrons between two atoms.
• One atom, the donor, has a complete octet and a lone pair of electrons, while the other, the acceptor, is electron-deficient.

Bonding between atoms A and B is:

• Ionic if there is a large difference in electronegativity.
• Covalent if A and B have similar electronegativity values.
• Coordinate if a lone pair on A (or B) is donated to electron-deficient B (or A).

Hydrogen Bond

• The electrostatic attraction between a hydrogen atom covalently bonded to a highly electronegative atom and another electronegative atom in the same or a different molecule.
• Hydrogen bonds are strongest in the solid state and weakest in the gaseous state, occurring in two main forms:
  • Intermolecular H-bonding (e.g., HF, water) increases solubility in water and boiling point.
  • Intramolecular H-bonding (e.g., o-nitrophenol) decreases solubility in water and boiling point.
• Compounds with O—H, N—H, or H—F bonds exhibit unusual properties due to hydrogen bonding, such as the high viscosity and boiling point of glycerol and the stability of proteins and nucleic acids.

Van der Waals’ Forces

• The sum of attractive or repulsive interactions between molecules, excluding covalent bonds and electrostatic interactions of ions with each other or neutral molecules.
• These forces are weaker than normal chemical bonds and include dipole-dipole interactions, London dispersion forces, and Debye forces.
• An example is the ability of geckos to climb sheer surfaces, attributed to van der Waals’ forces between their foot-pads and the surfaces.