Chapter 1: Problem 4

Describe the lattice structure and elemental composition of the mineral halite.

Short Answer

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Halite, also known as rock salt, has a chemical formula of NaCl and is composed of sodium (Na) and chloride (Cl) ions. It crystallizes in the cubic crystal system with a face-centered cubic (fcc) unit cell containing 4 Na+ and 4 Cl- ions. The lattice is highly ordered, as each ion is surrounded by six oppositely charged ions arranged at the vertices of a regular octahedron, resulting in strong ionic bonding.

Step by step solution

1. Introduction to Halite

Halite, commonly known as rock salt, is a mineral belonging to the halide group. It has the chemical formula NaCl, indicating that it is composed of sodium (Na) and chlorine (Cl) ions. Halite exhibits an ionic crystal structure, reflecting the strong electrostatic attraction between the positively charged sodium ions and the negatively charged chloride ions.

2. Crystal System of Halite

Halite crystallizes in the cubic crystal system. This system is characterized by three perpendicular axes of equal length, and all angles between these axes are 90 degrees. The crystal system is also known as isometric or regular, meaning that all three crystallographic axes are equal in length and orthogonal to each other.

3. Unit Cell of Halite

The unit cell is the smallest repeating unit in a crystal lattice that represents the entire crystal structure. The unit cell of halite is a face-centered cubic (fcc) structure, which means that there are ions at each corner and in the center of each face of the cube. In total, there are 4 sodium ions (Na+) and 4 chloride ions (Cl-) in one unit cell of halite, which amounts to a total of 8 ions.

4. Arrangement of Sodium and Chloride Ions

In the halite crystal lattice, each sodium ion (Na+) is surrounded by six chloride ions (Cl-) arranged at the vertices of a regular octahedron. Similarly, each chloride ion is surrounded by six sodium ions also arranged at the vertices of a regular octahedron. The closest distance between a Na+ ion and a Cl- ion is given by the edge length of the unit cell, which is equal to the sum of their ionic radii. This arrangement leads to a strong ionic bonding and a highly ordered lattice.

5. Summary

In conclusion, the mineral halite has an elemental composition of sodium (Na) and chloride (Cl) ions, forming an ionic crystal with a chemical formula of NaCl. The crystal structure belongs to the cubic crystal system, with a face-centered cubic unit cell. The arrangement of ions in the lattice is highly ordered, with each ion being surrounded by six oppositely charged ions arranged at the vertices of a regular octahedron.

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Describe the lattice structure and elemental composition of the mineral halite.

Short Answer

Step by step solution

1. Introduction to Halite

2. Crystal System of Halite

3. Unit Cell of Halite

4. Arrangement of Sodium and Chloride Ions

5. Summary

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