Difference Between Atomic Structure and Crystal Structure

Main Difference – Atomic Structure vs Crystal Structure

Although atoms are the smallest units that can be found in all matter, these atoms have a complex structure when experimentally analyzed. In order to understand almost all concepts in chemistry, it is essential to clearly understand the basic structure of an atom. Crystals are solid compounds made out of a number of atoms or molecules. There are particular arrangements in crystals. These arrangements are called crystal structures. Examining the crystal structure is very important in determining the properties of that compound. The main difference between atomic structure and crystal structure is that atomic structure describes the arrangement of subatomic particles in an atom whereas crystal structure describes the arrangement of atoms or molecules in a crystalline compound.

Key Areas Covered

1. What is Atomic Structure
      – Definition, Explanation of the Structure
2. What is Crystal Structure
      – Definition, Explanation of the Structure
3. What is the Difference Between Atomic Structure and Crystal Structure
      – Comparison of Key Differences

Key Terms: Atom, Atomic Structure, Covalent Network Crystals, Crystal Structure, Crystalline Structure, Crystallography, Ionic Crystals, Metallic Crystals, Orbital, Shell, Subshell

What is an Atomic Structure

Atomic structure is the arrangement of subatomic particles in an atom. Earlier, scientists believed that an atom is the smallest unit that can be found on earth and all matter is composed of atoms, but later experiments proved that atoms can be further divided into subatomic particles. Therefore, the concept of atomic structure came into discussion. Different scientists suggested different structures for an atom. But with the development of science and technology, the modern atomic theory, which clearly explains the structure of an atom, was developed.

According to modern atomic theory, an atom is composed of three types of subatomic particles named as electrons, protons, and neutrons. The protons and neutrons are in the middle of the atoms, forming a central core called nucleus. The electrons are in continuous movement around the nucleus in particular pathways. However, these electrons look like an electron cloud that surrounds the nucleus of the atom.

Figure 1: Atomic Structure of Helium

Since electrons are in continuous movement around the nucleus, we cannot determine the exact location of an electron at a time. We can only say the probability of finding an electron at a particular location. According to these probabilities, there are certain shells that electrons move in. These shells have their own quantized energy level. Thus, these shells are arranged according to the energy level of electrons present in those shells. The shell with the lowest energy is the nearest to the nucleus. These electron shells are named as K, L, M, N, etc. from the nucleus to the outside.

Electron shells can be further divided into subshells. These subshells are named as s subshell, p subshell, d subshell and f subshell. Except for s subshell, other subshells can be further divided into orbitals. Each orbital can hold a maximum of two electrons that have opposite spins.

Electrons are the major subatomic particles that participate in chemical reactions. However, protons and neutrons participate in nuclear reactions.

What is Crystal Structure

Crystal structure is the arrangement of atoms or molecules in a crystal. Solid compounds can be divided into three groups as crystalline compounds, semi-crystalline compounds, and non-crystalline compounds. Crystalline compounds have a well-organized structure. They have a three-dimensional organization. The crystal structure of a crystalline compound is called a lattice. The smallest unit of this organized structure is called a unit cell. This unit cell should represent the overall arrangement of the crystal.

There are three major structures proposed for the unit cell. They are simple cubic structure, body-centered cubic structure, and face-centered cubic structure. When considering the crystal structure, there are seven structures that a crystal can have that are named according to the symmetry. They are monoclinic, triclinic, trigonal, hexagonal, orthorhombic, tetragonal and cubic.

Figure 2: NaCl Crystal Structure

In addition, there are crystal structures that are named according to the type of chemical bond present in that crystal. They are ionic crystals, covalent network crystals, and metallic crystals. Ionic crystals are made out of cations and anions that are arranged in a regular, repeating structure. Covalent network crystals are composed of atoms or molecules attached to each other through covalent bonds forming a network of atoms or molecules. Metallic crystals are composed of metal cations surrounded by freely moving electrons.

Difference Between Atomic Structure and Crystal Structure

Definition

Atomic Structure: Atomic structure is the arrangement of subatomic particles in an atom.

Crystal Structure: Crystal structure is the arrangement of atoms or molecules in a crystal.

Structure

Atomic Structure: Atomic structure is a complex structure.

Crystal Structure: Crystal structure is a well-organized lattice structure.

Components

Atomic Structure: Atoms are composed of subatomic particles: electrons, protons and neutrons.

Crystal Structure: Crystals are composed of cations and anions or metal ions and free electrons.

Variations

Atomic Structure: The overall atomic structure is the same in all atoms.  

Crystal Structure: The crystal structures are different from each other depending on the components present in the crystal.

Conclusion

Atomic structure is important in understanding everything about chemistry. Crystal structure is important in identifying crystals, understanding the properties of crystals and to predict their reactions. The main difference between atomic structure and crystal structure is that atomic structure describes the arrangement of subatomic particles in an atom whereas crystal structure describes the arrangement of atoms or molecules in a crystalline compound.

Image Courtesy:

1. “Helium atom QM” By User:Yzmo – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “NaCl crystal structure” By Eyal Bairey (user: Eyal Bairey) – Own work (Public Domain) via Commons Wikimedia

References:

1. “Crystal Structures and the Unit Cell.” Study.com, Available here . Accessed 21 Sept. 2017.
2. “Crystal Structure (Theory).” Virtual Lab : Physical Sciences : Amrita Vishwa Vidyapeetham Virtual Lab, Available here. Accessed 21 Sept. 2017.