Solid State

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The solid-state topic in chemistry deals with the study of the structure, properties, and synthesis of solid materials. However, non-molecular solids are not necessarily,  exclusively solids. Therefore, there is a strong overlap with the solid-state of Physics, crystallography, mineralogy, ceramics, metallurgy, thermodynamics, materials science, and electronics with a focus on the synthesis of novel materials and their characterization. These can be classified as amorphous or crystalline depending on the nature of order present in them and the arrangement of their constituent particles.

One of these states is Solid-state. We have learned that matter exists in three states – solid, liquid, and gas. However, as we progress from lower to higher classes the concepts of states of matter, get more advanced and there are more things to learn. In this topic, we will be dealing with the concept of solid-state in a broader aspect to understand all the terms including the properties as well as the types of solids.

Solids generally have certain characteristics that set them apart from liquids and gases. If we look at the example then, they have the ability to resist any force that is applied to its surface. The solid-state, of compounds, largely depends on the properties of atoms such as forces acting between them, and their arrangement.

History

Since the direct relevance of the solid chemistry to products of commerce, solid-state inorganic chemistry has been driven strongly by technology. Often progress in this field has been fueled by the demands of industry, at times in collaboration with academia. In the 20th century, the applications discovered include Zeolite and Platinum-based catalysts for petroleum processing in the 1950s, as a core component of microelectronic high-purity silicon devices in the 1960s, and “high temperature” superconductivity in the 1980s. 

The invention of crystallography X-ray in the early 1900s by William Lawrence Bragg was an enabling innovation. Our understanding of at the atomic level in the solid-state was advanced considerably by Carl Wagner's work on oxidation rate theory, counter diffusion of ions, and defect chemistry. Owing to his contributions he is sometimes referred to as the father of solid-state chemistry.

Characterization

Characterization of Synthetic Methodology often goes hand in hand in the sense that not only one but a series of reaction mixtures are subjected to heat and prepared treatment. The stoichiometry is defined as a typically varied systematic way to find which stoichiometries will lead to solid solutions, new solid compounds, or between the known ones. 

A method that is very prime to characterize the reaction products is powder diffraction. It is because many solid-state reactions will produce polycrystalline powders ingots. Powder diffraction facilitates the identification of phases which are known in the mixture. If we found a pattern that is not known in the diffraction data libraries an attempt can be made to index the pattern for example to identify the size and symmetry of the unit cell. If the product which we have obtained is not crystalline then the characterization is typically much more difficult.

Once a new phase unit cell is known, the next step is to establish the stoichiometry of the phase. This can be done in various ways. The composition sometimes of the original mixture will give a clue, if one finds only one product - that is a single powder pattern- or if one was trying to make a phase of a certain composition by using analogy to known materials but this is very rare. 

The considerable effort often in refining the synthetic methodology is required to obtain a pure sample of the new material. If it is possible to separate the product from the rest of the reaction mixture elemental analysis can be used. Another way involves the generation of characteristic X-rays SEM and in the electron beam. The diffraction of X-rays is also used due to its imaging speed and capabilities of data generation.

Molecular Solids

The solids are divided into three categories.

1. Non-Polar Molecular

These solids are formed from atoms or molecules that share a nonpolar covalent bond. These molecules or atoms are held by London forces or weak dispersion forces.

• Physically the nature of non-polar solids is soft.

• They are insulators and they do not conduct electricity.

• They have a low melting point.

• For example, Cl2, H2, I2, etc.

2. Polar Molecular

• By polar covalent bonds, these solids are held together and the atoms or molecules are bonded by relatively stronger dipole-dipole interactions.

• The physical nature is soft and most of these are liquids or gases at room temperature.

• They have a higher melting point and do not conduct electricity than the non -polar molecular solids.

• For example, SO2, HCl, NH3 etc.

3. Hydrogen-Bonded Molecular

With Hydrogen, the solids contain polar covalent bonds, Oxygen, Fluorine, and Nitrogen atoms. In these solids, molecules are held together by strong hydrogen bonding. 

• These solids are hard.

• They don't conduct electricity.

• These solid physical states are volatile liquids or soft solids under room temperature.

• They also have a low melting point.

For example, H2O (in Ice form).