Section E: Answer the case-based question given below.
37.a The melting points and boiling points of some ionic compounds are given below:
| Compound | Melting Point (K) | Boiling Point (K) |
| \(NaCl\) | 1074 | 1686 |
| \(LiCl\) | 887 | 1600 |
| \(CaCl_2\) | 1045 | 1900 |
| \(CaO\) | 2850 | 3120 |
| \(MgCl_2\) | 981 | 1685 |
These compounds are termed ionic because they are formed by the transfer of electrons from a metal to a non-metal. The electron transfer in such compounds is controlled by the electronic configuration of the elements involved. Every element tends to attain a completely filled valence shell of its nearest noble gas or a stable octet.
i. Show the electron transfer in the formation of magnesium chloride.
ii. List two properties of ionic compounds other than their high melting and boiling points.
i. Electron transfer in the formation of magnesium chloride (MgCl₂):
Magnesium chloride (MgCl₂) is formed by the transfer of electrons from magnesium (Mg) to chlorine (Cl). Magnesium has electrons in its outer shell, while chlorine has electrons in its outer shell. Magnesium loses its two valence electrons to achieve the stable electron configuration of neon, and each chlorine atom gains one electron to achieve the stable electron configuration of argon.
Magnesium (Mg) has the electronic configuration: \(1s^2\), \(2s^2\), \(2p^6\), \(3s^2\), \(1s^2\), \(2s^2\), \(2p^6\), \(3s^2\).
Chlorine (Cl) has the electronic configuration: \(1s^2\), \(2s^2\), \(2p^6\), \(3s^2\), \(3p^5\).
The electron transfer can be shown as follows:
\(Mg\) → \(Mg^2{^+}\) + \(2e^−\)
\(Cl\) + \(e^−\) → \(Cl^−\)
Combining these reactions:
\(Mg\) + \(2Cl\) → \(Mg^2{^+}\) + \(2Cl^−\)
The overall reaction:
\(Mg\) + \(Cl_2\) → \(MgCl_2\)
ii. Properties of ionic compounds (other than high melting and boiling points):
Electrical conductivity in molten or aqueous state: Ionic compounds conduct electricity when they are melted or dissolved in water. In these states, the are free to move and carry electrical current.
In molten or aqueous state: Ionic compounds conduct electricity when molten or dissolved in water because the are free to move and carry an electric current.
Solubility in water: Many ionic compounds are soluble in water. Water molecules surround and separate the ions due to their , allowing the ionic compound to dissolve.
Solubility in water: Many ionic compounds are soluble in water. Water molecules surround and separate the ions due to their , allowing the ionic compound to dissolve.