Crystalline Solids

When the elements of a solid substance (atoms, molecules, or ions) are organised in a highly ordered microscopic structure, the result is a crystal lattice that extends in all directions, the material is referred to as a crystal or crystalline solid. Macroscopic single crystals may also be distinguished by their geometrical form, which is composed of flat faces with certain, typical orientations, which makes them easy to recognise. Crystallography is a branch of science that studies crystals and their creation. Solidification is the term used to describe the crystal formation process that occurs through mechanisms of crystal development.

Snowflakes, diamonds, and table salt are just a few examples of enormous crystals that exist. The majority of inorganic solids are polycrystals, which are composed of several small crystals that have fused together to form a single solid. Polycrystals may be found in a wide variety of materials, including most metals, minerals, ceramics, and ice. Amorphous solids are a third type of solid in which the atoms lack any periodic structure. Amorphous solids include materials such as glass, wax, and a wide variety of polymers.

Characteristics of Crystalline solids

• It is composed of a vast number of little crystals, each of which has a distinct geometrical shape that is distinct from the others.

• Crystalline solids are anisotropic in nature, which means that certain of their physical characteristics, such as electrical resistance or refractive index, alter depending on which direction they are measured in the crystals. This occurs as a result of a variation in the arrangement of particles in various directions.

• Cleavage of crystalline materials can only take place in one direction, hence we get clean cleavage in the case of crystalline solids.

• These are regarded as genuine solids by the scientific community.

• It is important to note that cooling curves of crystalline solids are not smooth, and there are breakpoints in the curve. 

• The heat of fusion is defined, and it is determined by the arrangement of the particles in the crystalline solids.

Classification of Crystalline Solids

There are four types of crystalline solids: ionic solids, molecular solids, network covalent solids, and metallic solids. 

Ionic solids

Ionic solids are the most common form of crystalline solid. Ionic solids are solids that include ions. Ionic compounds crystallise when two oppositely charged ions combine to create a crystal structure: a positively charged cation and a negatively charged anion. Because of the strong attraction that exists between opposing charges, it takes a great deal of energy to break down ionic compounds. Therefore, ionic compounds have extremely high melting points, which are frequently between 300 and 1,000 degrees Celsius (572 to 1,832 degrees Fahrenheit).

Molecular solids 

In molecular solids, electrostatic forces attract covalently bonded molecules that are attracted to one another by electrostatic forces. Because covalent bonding involves sharing electrons rather than the transfer of those particles, the shared electrons may spend more time in the electron cloud of the larger element, resulting in weak or shifting polarity. Electrostatic interaction between two poles (dipoles) is substantially less than ionic or covalent bonding, hence molecular solids have a lower melting temperature and tend to be more malleable than ionic crystals (many will melt at less than 100o C, or 212 F). The vast majority of molecular solids are nonpolar. They will not dissolve in water but will dissolve in nonpolar solvents such as benzene and isooctane, which are both hydrocarbons. Sugar, for example, is a polar molecular solid that dissolves readily in water. Molecular solids do not carry electricity.

Network covalent solids

Individual molecules do not exist in a network solid, which is a type of solid. It is covalently bound together in a continuous network, which results in the formation of enormous crystals. In a network solid, each atom is covalently connected to every other atom in its immediate vicinity. Network solids exhibit features that are comparable to those of ionic solids. They are solids that are exceedingly hard and brittle, with melting points that are extraordinarily high (higher than 1,000 C or 1,800 F). The difference between them and ionic compounds is that they do not dissolve in water and do not conduct electricity. Diamonds, amethysts, and rubies are all examples of network solids in nature.

Metallic solids

Metals are solids that are both malleable and ductile, and they are opaque and lustrous in appearance. While malleable indicates that they are flexible and can be formed into thin sheets, ductile means that they can be twisted into wires or twisted into wires. Unlike ionic and covalent bonding, the valence electrons in a metallic connection are neither contributed nor shared with the other electrons. Rather, the electron clouds of nearby atoms overlap, causing electrons to become delocalized as a result of the overlap. The electrons are able to flow freely from one atom to another within the crystal with remarkable ease.

Importance of crystalline solids

Crystals are used in a range of important applications, including the following:

• One of the few methods of chemical structure elucidation that may produce exceedingly exact structures without any ambiguity is X-ray crystallography (which, for the time being, can only be performed on crystals). It is standard practice to convert complicated chemical species (such as proteins or medications) into crystal form in order to identify their absolute structure, which would otherwise be exceedingly difficult to determine by other methods.

• Converting chemical species into their crystal form will frequently allow them to be distinguished from any other nearby species. Because of this, when extreme purity is desired (as is the case in commercial pharmaceutical manufacture), it is common practise to transform the product into crystals in order to separate it from the remainder of the fluid.

Conclusion

Crystalline solids, often known as crystals, are considered to be “real solids.” Minerals are crystalline solids that have a crystalline structure. Table salt, for example, is an example of this type of substance. Crystalline solids are made up of atoms, ions, and molecules that are organised in an ordered and symmetrical pattern that is repeated throughout the whole crystal. A unit cell is the smallest repeating structure in a solid, and it is similar to a brick in a wall in terms of size. A crystal lattice is a network of unit cells that join together to form a network. Crystalline solids contain a number of other distinguishing characteristics that distinguish them from other materials. They are typically incompressible, which means that they cannot be compressed into smaller forms as a result of compression. In the crystal, all of the bonds between the particles have the same strength as one another due to the repeated geometric structure of the crystal. Therefore, crystalline solids have discrete melting points, as heat will break all of the bonds at the same time when the solid is heated to a certain temperature.