i. In the formation of compound between two atoms A and B, A loses two electrons and B grains one electron.

A. What is the nature of bond between A and B?


B. Suggest the formula of the compound formed between A and B.


ii. On similar lines explain the formation of MgCl2 molecule.


iii. Common salt conducts electricity only in the molten state. Why?


iv. Why is melting point of NaCl high?

i. A) The nature of bond between A and B will be ionic, as transfer of electrons is taking place forming an ionic compound.


(Ionic bond is a bond formed between two dissimilar atoms that have a large electronegativity value difference in between them. One atom loses electrons while another atom gains electrons to acquire a stable electronic configuration. )


B) The formula of the compound formed between A and B is AB2. (A loses electrons while B gains one electron)


ii) Magnesium chloride or MgCl2 is an ionic compound. Ionic compounds are formed due to the electrostatic force of attraction between oppositely charged ions. Magnesium chloride is made of Mg2+ and Cl- ions. One atom of magnesium has 12 electrons so when it loses two electrons, the number of electron sin the outermost shell is 8 electrons. Similarly, an atom of chlorine has 17 electrons so when it gains one electron, the number of electrons in the outermost shell now is 8. (Magnesium forms cation with charge +2 while Chlorine forms anion with charge -1) So therefore two chlorine anions form an ionic bond with one magnesium cation to form MgCl2.


iii) Common salt conducts electricity only in the molten state because for conduction of electricity, charged ions must be present in free state so that they can move about freely conducting the electricity. In ionic compounds like common salt or sodium chloride, the ions are not free but are ionic bonded in a crystal lattice hence cannot conduct electricity. However when they are in a molten state, ionic compounds (here NaCl) dissociates into Na+ and Cl-, these ions have mobility and are charge carriers and therefore common salt in the molten state can conduct electricity.


iv) Sodium combines with chlorine forming sodium chloride by ionic bond. This leads to a crystal lattice with a regular arrangement of ions held by strong forces. There is a strong electrostatic attractions between the positive and negative ions hence a lot of energy is required to overcome them hence the melting point is high.


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