Science: Chemical Bonding: Properties of Ionic Compounds and Covalent Substances (For CBSE, ICSE, IAS, NET, NRA 2022)

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Why Atoms Combine

  • Noble gases namely helium, neon, argon, krypton, xenon and radon did not react with other elements to form compounds i.e.. they were non – reactive, atoms having 8 electrons in their outermost shell are very stable and they did not form compounds. It was also observed that other atoms such as hydrogen, sodium, chlorine etc. which do not have 8 electrons in their outermost shell undergo chemical reactions. They can stabilize by combining with each other and attain the above configurations of noble gases i.e.. 8 electrons (or 2 electrons in case of helium) in their outermost shells.
  • This is the basic cause of chemical bonding. This attainment of eight electrons for stable structure is called the octet rule. The octet rule explains the chemical bonding in many compounds.

Ionic Bond

The chemical bond formed by transfer of electron from a metal to a non- metal is known as ionic or electrovalent bond. For example, when sodium metal and chlorine gas are brought into contact, they react violently, and we obtain sodium chloride.

This reaction is shown below:

Ionic Bond

2Na (s) + Cl2 (g) ⇾ 2NaCl (s)

Properties of Ionic Compounds

  • Physical State: Solid , Crystal , Brittle.
  • Melting and boiling points: have high melting and boiling points.
  • Electrical Conductivity: Conduct electricity in their molten state and in aqueous solutions.
  • Solubility: Ionic compounds are generally soluble in water but are insoluble in organic solvents such as ether, alcohol, carbon tetrachloride.

Covalent Bond

The bond, which is formed by sharing of electrons between the atoms is called a covalent bond . This bond forms when the forces of attraction and repulsion balance each other and the potential energy is minimum. Formation of covalent bond in H2 can be shown as,

H. + . H ⇾ H: H ⇾ H2

The bond consisting of two covalent bonds is also known as a double bond.

The bond which consists of three covalent bonds is known as a triple bond.

Properties of Covalent Substances

  • Physical State: Weak forces hence exists as solid , liquid and gas.
  • Melting and boiling points: have Lower melting and boiling points then ionic bonds.
  • Electrical Conductivity: Do not Conduct electricity.
  • Solubility: not soluble in water, but soluble in organic solvent like alcohol.

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