In nature one comes across several types of solids. Many solids are aggregates of atoms. The arrangement of atoms in any solid material is determined by the character, strength and directionality of the chemical binding forces, cohesive forces or chemical bonds.
The atoms, molecules or ions in a solid state are more closely packed than in the gaseous and liquid states and are held together by strong mutual forces of attraction and repulsion. Solids are the most obvious state of matter, they are ubiquitous and come in all shapes and sizes Solids are classified as either crystalline solids or amorphous solids.
Crystalline SolidBack to Top
Crystalline solids are characterized by their rigid and incompressible nature with sharp and high melting points. Many of the crystalline solids exhibit an anisotropic behavior in their physical, optical, mechanical and electrical properties. Crystalline solids have a highly ordered arrangement of constituent atoms, ions or molecules in a three-dimensional layer or lattice giving rise to distinct geometrical shapes.
Thee are two important types of crystalline solids.
- Ionic solids (represented by sodium chloride)
- Molecular solids (represented by sucrose)
The third type of crystalline solid is represented by elements such as graphite and diamond, boron, silicon and al metals. These substances which contain atoms of only one element covalently bonded to each other are called atomic solids.
An ionic solid contains ions, a molecular solid contain molecules and an atomic solid contains atom. Examples of three types of crystalline solids are diagrammatically represented below.
Amorphous SolidBack to Top
Amorphous material are condensed phases which do not possess the long range translational order or periodicity characteristics of a crystal.
- In amorphous solids the constituents are not arranged in a regular or oderly manner over a long range.
- Such solids do not have sharp melting points.
- These are considered pseudo solids.
- These show isotropy, that is same physical properties in all directions due to irregular arrangement.
- They do not show clean cleavage. They have an irregular cut.
Some of the examples of amorphous solids are rubber, pitch, plastic, glass etc.
ComparisonBack to Top
|Properties||Crystalline solids||Amorphous solids|
|Structure||The constituent particles, atoms, ions or molecules are arranged in regular and definite three dimensional pattern. Eg, sodium chloride, diamond, sugar etc.||The constituent particles are arranged in irregular three dimensional pattern.|
|Cutting with a knife||Gives clean, sharp cleavage.||Unclean cleavage.|
|Compressiblity||Rigid and incompressible.||Usually rigid and cannot be compressed to any appreciable extent.|
|Melting point||They have sharp and definite melting point.||Melting point is not definite. Melt over a range of temperature.|
|Heat of fusion||Definite||Not definite.|
|Physical properties||These are anisotropic that is their physical properties are not identical in all directions.||These are isotropic that is their physical properties are identical in all directions.|