Question

In which of the following structures, the anion has maximum coordination number? (a) \(\mathrm{NaCl}\) (b) \(\mathrm{ZnS}\) (c) \(\mathrm{CaF}_{2}\) (d) \(\mathrm{Na}_{2} \mathrm{O}\)

Short answer

The anion in NaCl has the maximum coordination number, which is 6.

Step-by-step solution

Understand Coordination Number

Coordination number of an ion refers to the number of opposite charged ions that surround it in a crystal lattice. Different structures have different arrangements which dictate different coordination numbers for the cations and anions.

Determine the Coordination Number for Each Option

Analyze each given structure to determine the coordination number of the anions. For NaCl, each chloride ion is surrounded by 6 sodium ions, so its coordination number is 6. In ZnS, each sulfide ion is surrounded by 4 zinc ions, so its coordination number is 4. For CaF2, each fluoride ion is surrounded by 4 calcium ions, so its coordination number is 4. In Na2O, each oxide ion is surrounded by 4 sodium ions, so its coordination number is 4.

Compare Coordination Numbers

Compare the coordination numbers obtained for the anions in each structure to determine the one with the maximum coordination number.

Key concepts

Crystal Lattice

The crystal lattice represents the highly ordered structure of atoms or molecules in a crystalline solid. Think of it as an intricate 3D grid, where each point, known as a lattice point, is occupied by an atomic or ionic constituent that repeats throughout the entire crystal. This repetitive pattern is often referred to as the unit cell, and it's the basic building block of the crystal.

The arrangement within a crystal lattice is not haphazard; it is determined by the size and shape of the constituent particles and the forces of attraction between them. Hence, the lattice structure affects physical properties such as melting point, hardness, and density.

The concept of a crystal lattice is fundamental when exploring the coordination number in ionic compounds, as it speaks to how ions are surrounded and held together within the solid, affecting overall stability and other chemical properties.

Ionic Compounds

Ionic compounds are substances composed of positive and negative ions that are held together by strong electrostatic forces known as ionic bonds. These compounds typically consist of a metal cation (positive ion) and a non-metal anion (negative ion). Their formation is the result of atoms either losing or gaining electrons to achieve a stable electron configuration, often visualized as a noble gas structure.

When dissolving in water or melting, ionic compounds typically conduct electricity, due to the free movement of ions. In the solid state, they form a rigid lattice structure where each ion is surrounded by ions of opposite charge. This surrounding defines the coordination number, which varies based on the specific packing and size of the ions within the crystal lattice. For example, in a sodium chloride (NaCl) crystal structure, each sodium ion is coordinated by six chloride ions and vice versa, indicating a coordination number of 6.

Chemical Bonding

Chemical bonding is the physical phenomenon responsible for the attractions between atoms and molecules, and it's what holds compounds together. There are three primary types of chemical bonds: ionic, covalent, and metallic.

Ionic bonding occurs when there is a complete transfer of electrons between atoms, forming ions that are held together by electrostatic forces. Covalent bonding, on the other hand, involves the sharing of electrons between atoms, usually seen in compounds composed of non-metals. Metallic bonding is characteristic of metals, where electrons are shared and able to move freely among a lattice of metal cations.

In the context of crystal structures and ionic compounds, understanding chemical bonding helps explain why certain arrangements are more stable and how ions bind together in a solid. The strength and type of bond in the structure dictate its properties, such as hardness, melting point, and electrical conductivity. As such, the analysis of chemical bonds is essential to determine the coordination number in ionic compounds within the crystal lattice.