Atomic Structure vs Crystal Structure
In this article, main focus is on the internal arrangement of an atom and a crystal. What we see from outside is a result of the internal arrangement of atoms or molecules. Sometimes, the external view may be different from the internal structure; but they are not completely independent of each other.
Atoms are the small building blocks of all existing substances. They are so tiny that we can’t even observe with our naked eye. Normally, atoms are in the Angstrom range. With the discovery of subatomic particles, the next question for scientists was to find how they are arranged in an atom. In 1904, Thompson presented the plum pudding model to explain the atomic structure. This said that electrons are scattered in a sphere where there are also positive charges scattered to neutralize the negative charges. The dispersion of electrons is like scattering of plums in a pudding, hence got the name “plum pudding model”. Later Ernest Rutherford did an experiment that led to the finding of more accurate details about the atomic structure. They fired alpha particles to a thin gold foil and found out following data.
• Most of the alpha particles passed through the gold foil.
• Few of the particles were deflected.
• Some of the alpha particles bounced back straightly.
These observations helped them to come to the following conclusions.
• Alpha particles are positively charged. Most of them were passing through the gold foil means there are a lot of free spaces inside.
• Some were deflected because they were passing near another positive charge. But the number of deflections is very low, meaning that the positive charged are concentrated into few spots. And this place was named as the nucleus.
• When the alpha particle directly encounters a nucleus it bounces back directly.
With the above experiment findings and based on many other later experiments, the atomic structure was described. Atom is made up of a nucleus, which has protons and neutrons. Other than neutrons and positrons there are other small sub atomic particles in the nucleus. And there are electrons circling around the nucleus in orbitals. Most of the space in an atom is empty. The attractive forces between the positively charged nucleus (positive charge due to protons) and the negatively charged electrons maintain the atom’s shape.
Crystal structure is how the atoms or molecules are arranged in a crystal. This has a three dimensional arrangement in space. Normally, in a crystal, there is a repeating arrangement of certain atoms or molecules. One of the repeating units of a crystal is named as a “unit cell.” Because of this repeating arrangement, there is a pattern and a long range order in a crystal. The crystal structure determined many of its physical and chemical properties such as electronic band structure, cleavage, transparency, etc. There are seven crystal lattice systems, which are categorized based on their shape. They are cubic, tetragonal, orthorhombic, hexagonal, trigonal, triclinic and monoclinic. According to the properties also crystals can be categorized as covalent, metallic, ionic, and molecular crystals.
What is the difference between Atomic Structure and Crystal Structure?
• Atomic structure gives an idea of the shape of an atom and how the sub atomic particles are arranged in an atom. Crystal structure tells about how the atoms or the molecules are arranged in a crystal solid or a liquid.
• Overall atomic structure is common to all the atoms except the number of sub atomic particles. But there are a large number of crystal structure variations.