Danielle has taught middle school science and has a doctorate degree in Environmental Health
Did you know crystal solids have a certain arrangement? Learn about this arrangement, called a crystal lattice, and explore their structures. Test yourself at the end of this lesson by taking a short quiz.
What Is A Crystal Lattice?
Do you know what common table salt (NaCl) and a beautiful, shiny diamond have in common? I know what you're thinking - how on earth could the salt on your french fries have anything in common with the expensive diamonds found in jewelry? Well, based on their structure, they are both solid objects that contain tiny crystals interlocking together.
In chemistry, crystals are a type of solid material composed of atoms or groups of atoms that are arranged in a three-dimensional pattern that is very ordered. In a crystal, the groups of atoms are repetitive at evenly spaced intervals, all maintaining their orientation to one another. In other words, the geometric shape of a crystal is highly symmetrical. When you see the word 'symmetrical,' think about the perfect proportion and balance of these atoms in a crystal. Now that we know what a crystal is, and that is can be found inside our table salt and a sparkly diamond, let's look at crystal lattices.
A crystal lattice is the arrangement of these atoms, or groups of atoms, in a crystal. These atoms or groups of atoms are commonly referred to as points within a crystal lattice site. Thus, think of a crystal lattice site as containing a series of points arranged in a specific pattern with high symmetry. Note that these points don't tell you the position of an atom in a crystal. They are simply points 'in space' oriented in such a way to build a lattice structure.
Crystal Lattice Structure
As we look at the structure of a crystal lattice, keep in mind the patterns of arrangement of each point as well as their symmetry. Crystal lattice sites are only viewed microscopically and are invisible to the naked eye. In order to view these structures, we must take a crystal (solid object), place it under a microscope, and view the crystal lattice sites.
The structure of a crystal lattice is shown here. Recall that a crystal lattice is the arrangement of atoms in a crystal (the black and white points in the image here are your atoms). This arrangement can be defined as the intersection of three parallel planes. So, if we slice this diagram into three parts you will see three different planes. When these planes intersect with one another, the result is a three-dimensional network that has faces. Think of each face as a box that is arranged in a parallel manner.
Diagram 1: Example of a Crystal Lattice Structure
You don't think I would forget about our friend symmetry, did you? Certainly not; in fact, these boxes (or faces) contribute to the symmetry of a crystal lattice structure. Each box contains the symmetry information required to ensure the crystal structure is translational.
Translational symmetry occurs when an object moves (or translates) at a certain distance in a certain location. For example, let's say you would like to build a patterned wood floor. You lay one style of wood down, diagonally, every 20 inches. This style of wood, in a particular pattern, has a certain distance (20 inches) and direction (diagonal).
Crystal lattices can be classified as either monatomic or polyatomic. This classification is based on the kind of atoms present in the face within a lattice structure. If there is only one type of atom used to make a face (or box), this is monoatomic. A polyatomic crystal lattice contains more than one type of atom used to make a face.
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If we look at the crystal lattice structure of table salt (NaCl) - lattice (a), and a diamond - lattice (b), we will see they both have different lattice structures. One face in table salt is composed of points that are red and green. This means there is more than one type of atom present. Hence, this structure is polyatomic. With the diamond lattice structure, there is only one colored point (blue). This structure is monatomic.
Diagram 2: Crystal Lattice Structures of (a) NaCl and (b) Diamond
Types of Crystal Lattice Structures
There are 14 different types of crystal lattices. Each type uniquely describes the geometrical symmetry of a crystal. Specifically, these crystal lattice types are called Bravais lattices. A Bravais lattice simply describes the different types of three different lattices that can be produced for a given crystal.
Each of the 14 lattice types are classified into 7 crystal systems. Think of each system as a group of crystal lattice structures (Bravais lattices) that uniquely describe the geometrical symmetry of a crystal. Tables listing the seven systems and their structures are provided. If we go back to our example of table salt, what type of crystal system do you think it belongs to? That's right! Table salt (NaCl) belongs to the cubic lattice system.
Table 1: List of Crystal Systems
Table 2: List of Crystal Systems, Continued
Table 3: List of Crystal Systems, Continued
Crystal lattices are fundamental to the structure of a solid object. The next time you pour salt over your food or clean that sparkly diamond, remember the highly ordered crystal lattice structure used to make that object.
Most solid objects contain tiny, interlocking crystals. A crystal is a solid material that contains atoms or groups of atoms arranged in a highly ordered structure. This structural arrangement is three-dimensional. A crystal lattice describes the arrangement of these atoms in a crystal and characterized as having translational symmetry. If there is one type of atom present in the face of a crystal lattice, it is called monatomic. The presence of more than one type of atom means the lattice structure is polyatomic. There are 14 different types of crystal lattices called Bravais lattices. Each of these lattice structures are classified into seven crystal systems.
Crystal Lattice Key Terms
Crystal: solid matter containing atoms or atom groups arranged in an ordered structure
Crystal Lattice: atom arrangements in crystal forms with translational symmetry
Monatomic: only one type of atom in the lattice
Polyatomic: more than one type of atom in the lattice
Bravais Lattices: 7 crystal systems made up of 14 different crystal lattice types
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