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Metals and Non-metals - Formation and properties of ionic compounds

Grade 10CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Ionic compounds, also known as electrovalent compounds, are formed by the transfer of electrons from a metal to a non-metal.

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Metals lose their valence electrons to form positive ions called cations (e.g., Na+Na^+, Mg2+Mg^{2+}), achieving a stable noble gas configuration.

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Non-metals gain electrons to form negative ions called anions (e.g., Cl−Cl^-, O2−O^{2-}), also achieving a stable noble gas configuration.

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The strong electrostatic force of attraction between the oppositely charged ions holds them together in a crystal lattice structure.

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Physical Nature: Ionic compounds are solids and are generally brittle; they break into pieces when pressure is applied.

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Melting and Boiling Points: They have high melting and boiling points because a large amount of energy is required to break the strong inter-ionic attraction.

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Solubility: Electrovalent compounds are generally soluble in water (polar solvent) but insoluble in solvents such as kerosene and petrol (non-polar solvents).

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Conduction of Electricity: They do not conduct electricity in the solid state because ions are not free to move. However, they conduct electricity in the molten state or when dissolved in water (aqueous solution) as ions become free.

📐Formulae

Na→Na++e−Na \rightarrow Na^+ + e^-

Cl+e−→Cl−Cl + e^- \rightarrow Cl^-

Na++Cl−→NaClNa^+ + Cl^- \rightarrow NaCl

Mg→Mg2++2e−Mg \rightarrow Mg^{2+} + 2e^-

2Cl+2e−→2Cl−2Cl + 2e^- \rightarrow 2Cl^-

Mg2++2Cl−→MgCl2Mg^{2+} + 2Cl^- \rightarrow MgCl_2

💡Examples

Problem 1:

Explain the formation of Magnesium Chloride (MgCl2MgCl_2) using electron dot structures.

Solution:

Magnesium (MgMg) has an atomic number of 1212 and electronic configuration 2,8,22, 8, 2. It loses 22 electrons to form Mg2+Mg^{2+}. Chlorine (ClCl) has an atomic number of 1717 and electronic configuration 2,8,72, 8, 7. It needs 11 electron to complete its octet. Therefore, one MgMg atom transfers its 22 electrons to two ClCl atoms, resulting in [Mg]2+[Mg]^{2+} and 2[Cl]−2[Cl]^- ions.

Explanation:

The transfer of electrons ensures that both the metal and non-metal achieve a stable octet configuration. The resulting ions are held by strong electrostatic forces to form the ionic compound MgCl2MgCl_2.

Problem 2:

Why do ionic compounds have high melting points?

Solution:

Ionic compounds consist of a regular arrangement of cations and anions held together by very strong electrostatic forces of attraction.

Explanation:

To overcome these strong inter-ionic forces and move the ions out of their fixed positions in the lattice, a significant amount of thermal energy is required. Hence, NaClNaCl has a melting point of approximately 1074 K1074 \, K.

Problem 3:

Why does a solution of Sodium Chloride (NaClNaCl) conduct electricity, while solid NaClNaCl does not?

Solution:

In the solid state, ions are held in a rigid structure by strong forces and cannot move. In an aqueous solution or molten state, these forces are weakened, allowing ions to move freely toward electrodes.

Explanation:

Electricity is the flow of charge. Since ions are the charge carriers in ionic compounds, their mobility in the liquid phase allows for the conduction of electric current.