Crystalline and Amorphous Solid Materials
Crystalline solid like molecular, ionic, covalent crystal, and metallic crystalline solids has define the orderly arrangement of constituents elements like atoms, ions, or molecules but amorphous solid materials have indefinite types of structure. From the definition of crystalline and amorphous solids, carbon forms diamond crystals and amorphous solid materials like carbon black. Crystals and amorphous solid materials are hard and rigid due to the absence of the translatory kinetic motion of the structural units. The learning of the definite geometrical dimensions of crystalline solids is termed as crystallography. Bragg diffraction experiment in physical or chemical science is very useful for crystal structure analysis. They developed the very simple relation between wavelengths of the x-ray electromagnetic radiation spectrum line and spacing between the lattice planes.
Molecular Solid Material
A solid molecule is characterized by its definite shape, mechanical strength, density and rigidity rather than liquid and gases. The rigidity presence due to the absence of the translatory moment of the structural unit of the solid. These units fixed to their mean position with strong forces of attraction between these units. According to geometrical structure and properties, solid are classified mainly into two types, crystalline or crystals solid and amorphous solid materials.
Definition of Crystalline solid
Solid which posses a definite structure, sharp melting point, and symmetrical arrangement of constituents are called crystalline solid. Therefore, these properties result to form a high degree of internal order that extends in a definite pattern. They show long-range order in the crystal. For example, sodium chloride, potassium chloride, sugar, and ice, quartzes are the crystalline solid material that has to melt by the specific heat and definite geometrical structural arrangement.
Types of Crystalline Solids
On the basis of the nature of force operating between constituent particles meanings atoms, ions, molecules, solid crystals are classified into four categories.
Molecular Crystals Material
Van der Waals’s types of forces hold the constituents in the molecular crystalline solid material. The forces are interatomic or intermolecular in this crystal lattice originating from the dipole-dipole attraction. The forces which combine the molecules are weak Van der Waals or London dispersion forces. Molecular crystals found in carbon dioxide, nitrogen, mica, borax, boric acid, etc, and most of the organic hydrocarbon like olefin. According to the binding molecule, the molecular crystals are three types, non-polar, polar and hydrogen bonding crystalline soils.
Non-Polar Crystal Solids
Some of the molecular crystals are non-directional nature due to the absence of the dipole moment. For example, hydrogen, helium, oxygen, chlorine, carbon dioxide, methane molecule, etc. Therefore, the forces operating between constituent molecules also a weak London dispersion force.
Polar Binding Crystal solids
The polar binding crystal has polarity in the constituent’s molecules. Sulfur dioxide and ammonia are common examples of this type of crystalline solid. Due to polarization the constituent’s elements also binding by low forces of attraction.
Hydrogen-Bonded Crystalline Solids
Hydrogen atom carries OH-group and some positive charge attracted to electronegative atoms like oxygen and nitrogen by linking is called hydrogen bonding. The common example is seen in the dimer of formic or acidic acid. The hydrogen bond is electrostatic in nature but very weak with bond energy 5 to 6 kcal. The most discussed example of hydrogen-bonded crystalline solid is ice where oxygen atom surrounded by four hydrogen atoms at the corned of the tetrahedron. Organic materials like alcohol, carboxylic acids, proteins also form hydrogen-bonded crystalline solids.
Ionic Crystalline Solids
In many crystals like sodium chloride, potassium chloride, calcium carbonate, etc the structural units are ion and electrostatic forces operating between these ions. Two forces that operate in ionic crystalline solids, electrostatic attraction forces between the opposite ions and repulsion effect between the nucleus and inner shell electrons. When attractive and repulsive forces balancing by lowering potential energy the ionic crystal is most stable. This minimum potential or ionization energy in chemical science is the lattice energy but opposite in sign. Therefore ionic crystalline solids have a high melting point, strong and likely to brittle.
Covalent Crystalline Solid
In many crystals, the atoms in the structural units held together by covalent forces or bonding by pairing electrons of hybridized orbitals to form the giant type molecules. Diamond, germanium, zink sulfide, silver iodide, silicon carbide are well-known examples of covalent bonding crystalline solids. In diamond, every carbon atom is covalently linking with the other four carbon atom along the tetrahedron.
Metallic Crystals Solid Materials
Electron held loosely in these types of crystals structure of metal elements in the periodic table. Therefore, they are good conductors of electric energy. Metallic crystalline solid can be bent and strong. The metallic crystal usually the body-centered or face-centered cubic and closed packed hexagonal crystalline solid. In closed paced and hexagonal form, every atom surrounded by 12 other metal atoms by the metallic bond with coordination number twelve.
Properties of Common Crystalline Solids
- In the crystalline solid, the constituents may be atoms, ions, molecules.
- Crystalline solids have the properties of sharp melting points, flat faces, and sharp edges. It has a well-developed form and usually arranged symmetrically.
- Definite and the ordered arrangement of the constituents extends over a large distance.
- Crystalline solids belonging to the cubic class shows enantiotropic properties. But the magnitude of the enantiotropic properties depends on the direction of measurement.
Definition of Amorphous Solid
Amorphous materials define as a solid which does not possess definite structure, sharp melting point, and the constituents do not form an order arrangements. Therefore, the constituents extend over a short-range, called short-range order. Glass, pitch, rubber, plastics, etc has the properties of amorphous solids.
Amorphous solid materials define many characteristics of crystalline such as shape rigidity and hardness but do not order arrangement and melt gradually over a range of the temperature. Hence amorphous solids are considered as supercooled liquids rather than solid.
Differences of Crystalline and Amorphous Materials
- Crystals meanings a definite structure and a sharp melting point. But amorphous that do not define a definite structure and sharp melting point.
- The constituents of crystalline material are ordered arrangement which extends over a long-range. But in an amorphous material define the constituents that do not have order arrangement.
Crystals Properties of Diamond
Each sp3 hybridized carbon meanings tetrahedrally surrounded by four other carbon atoms with the carbon-carbon chemical bond distance of 154 pm in the diamond crystals. These tetrahedral structures form a cubic crystal unit of the diamond.
Crystalline and Amorphous form of Carbon
Carbon has several covalent crystallines and amorphous solid allotropic forms in nature. Diamond crystals and graphite excellent examples of crystalline solid for learning chemistry. Material like carbon black, soot, etc. are amorphous solid but all of these forms micro-crystalline structure. Therefore, graphite consists of the layer structure in each layer of the carbon atoms with sp2 hybridized energy levels arranged in hexagonal planner arrangement with free pi-electrons. Hence the pi-electrons responsible for the electrical conductivity of amorphous graphite material. Successive layers of carbon-atoms attached by weak van der Waals forces with separation of layers 335 pm.
Four other rare and poorly understood properties of carbon crystal are β-graphite, Lonsdaleite or hexagonal diamond, Chaoite (very rare mineral), and carbon VI. But the last two forms of carbon appear to contain -C≡C-C≡C- and closer to the diamond in their properties. Therefore, carbon has properties to forms both crystalline solid and amorphous materials for our environment.