Why are ionic compounds usually hard?

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Detailed Solution

Ionic compounds are crystalline solids formed by tightly packed ions of opposite charges. They typically form when metals react with non-metals.

Formation of Ionic Compounds

In an ionic compound, a metal loses electrons while a non-metal gains electrons to complete its valence shell and achieve stability, usually mimicking the electron configuration of the nearest noble gas.
The resulting cations (positive ions) and anions (negative ions) are held together by ionic bonds, which are electrostatic forces of attraction between oppositely charged ions.
This electrostatic attraction is the main reason why ionic compounds are hard and rigid.

Crystal Structure

The ions are arranged in a crystalline lattice, where oppositely charged ions are packed tightly, giving the compound its characteristic hardness.

Example – Formation of NaCl

Sodium (Na) loses an electron to form a cation:

Na → Na⁺ + e⁻

Chlorine (Cl) gains an electron to form an anion:

Cl + e⁻ → Cl⁻

Na⁺ and Cl⁻ ions form an ionic bond to produce sodium chloride:

Na⁺ + Cl⁻ → NaCl

Additional Information

There are three main types of bonds formed between elements: