Chemical Bonding- ICSE-Class 10|Biswajit Das

1. Introduction to Chemical Bonding 🤝

A chemical bond is the force of attraction that holds atoms together to form molecules or ions. Atoms bond to achieve a stable electronic configuration, typically a complete outermost shell, like that of the noble gases (an octet of electrons, or a duet in the case of hydrogen and helium). This is known as the Octet Rule.

Chemical bonds are primarily of two types:

• Ionic (Electrovalent) Bonds
• Covalent Bonds

2. Ionic (Electrovalent) Bonding 🔗

An ionic bond is formed by the complete transfer of one or more electrons from a metal atom to a non-metal atom. This results in the formation of oppositely charged ions which are held together by a strong electrostatic force of attraction.

• Conditions for Ionic Bonding:
  • A low ionization potential for the metal atom (easy to lose electrons).
  • A high electron affinity for the non-metal atom (easy to gain electrons).
  • A large electronegativity difference between the two atoms.
• Formation of Ionic Compounds:
  • The metal atom loses electrons to form a positively charged ion, called a cation.
  • The non-metal atom gains electrons to form a negatively charged ion, called an anion.
  • The electrostatic attraction between the cation and anion forms the ionic bond.
• Example: Formation of Sodium Chloride (NaCl)
  • Sodium (Na) has 1 valence electron and a low ionization potential. It transfers this electron to chlorine.Na→Na++e−
  • Chlorine (Cl) has 7 valence electrons and a high electron affinity. It accepts the electron to complete its octet.Cl+e−→Cl−
  • The electrostatic attraction holds the ions together.Na++Cl−→NaCl
• Properties of Ionic Compounds:
  • They are generally crystalline solids with a high melting and boiling point.
  • They are soluble in polar solvents like water and insoluble in non-polar solvents.
  • They conduct electricity in the molten state or in aqueous solution, but not in the solid state.
  • They are brittle.

3. Covalent Bonding 🤝

A covalent bond is formed by the mutual sharing of electrons between two atoms, typically non-metals. This allows both atoms to achieve a stable electronic configuration.

• Types of Covalent Bonds:
  • Single Covalent Bond: Formed by the sharing of one pair of electrons. Example: H2​.
  • Double Covalent Bond: Formed by the sharing of two pairs of electrons. Example: O2​.
  • Triple Covalent Bond: Formed by the sharing of three pairs of electrons. Example: N2​.
  • Coordinate (Dative) Bond: A special type of covalent bond where both shared electrons are contributed by only one of the two atoms. Example: The ammonium ion (NH4+​) and the hydronium ion (H3​O+).
• Formation of Covalent Compounds (Example: Water, H2​O)
  • Oxygen has 6 valence electrons and needs 2 more to complete its octet.
  • Each hydrogen atom has 1 valence electron and needs 1 more for a duet.
  • The oxygen atom shares one electron with each hydrogen atom, and each hydrogen atom shares its electron with oxygen. This forms two single covalent bonds.
• Properties of Covalent Compounds:
  • They are generally gases, liquids, or soft solids with low melting and boiling points.
  • They are insoluble in water but soluble in non-polar solvents.
  • They are poor conductors of electricity in all states.
  • They are non-brittle.

4. Comparison of Ionic and Covalent Bonding