Definition
As we know, all material substances can exist in three basic states: liquid, solid, and gaseous. True, there is also a state of plasma, which scientists consider no less than the fourth state of matter, but our article is not about plasma. The solid state of a substance is therefore solid because it has a special crystalline structure, the particles of which are in a certain and clearly defined order, thus creating a crystal lattice. The structure of the crystal lattice consists of repeating identical elementary cells: atoms, molecules, ions, and other elementary particles connected by various nodes.
Structure and state of aggregation of substances
There are three states of aggregation: solid, liquid and gas. Each of them assumes a certain arrangement of particles. Below we will describe in more detail how the crystal lattice and the aggregative state of a substance are related in chemistry, but for now we will highlight the general principles.
- If the particles move chaotically, and the distance between them is many times greater than their own sizes, it is a gas . Due to the great distance from each other, the molecules and atoms in such a substance weakly interact with each other.
- If the particles are still arranged randomly, but at a small distance from each other, it is a liquid . In the liquid state of a substance, its molecules and atoms have stronger bonds that are more difficult to break.
- If the particles are collected close to each other and in a certain order, it is a solid . In this state, the connections between them are strongest. Particles can only move within their location and hardly move in space.
Most substances can be in a solid, liquid, or gaseous state, and depending on pressure and temperature, they can easily change from one to another. A typical example is water, which turns into steam when heated and becomes solid ice when cooled.
Types of gratings
Depending on the particles of the crystal lattice, there are fourteen types of it, here are the most popular of them:
Metal crystal lattice.
Next, we will describe in more detail all types of crystal lattice.
Crystal lattices
The crystal lattice is the spatial arrangement of atoms or ions in a crystal. The points of the crystal lattice at which atoms or ions are located are called lattice nodes.
Crystal lattices are divided into molecular, atomic, ionic and metallic.
It is very important not to confuse the type of chemical bond and crystal lattice. Remember that crystal lattices reflect the spatial arrangement of atoms.
Molecular crystal lattice
Molecules are located at the nodes of a molecular lattice. Under normal conditions, most gases and liquids have a molecular lattice. Bonds are most often covalent polar or nonpolar.
The classic example of a substance with a molecular lattice is water, so associate the properties of these substances with water. Substances with a molecular lattice are fragile, have low hardness, are volatile, fusible, capable of sublimation, and are characterized by low boiling points.
Examples: NH3, H2O, Cl2, CO2, N2, Br2, H2, I2. I would especially like to mention white phosphorus, orthorhombic, plastic and monoclinic sulfur, and fullerene. We studied these allotropic modifications in detail in an article devoted to the classification of substances.
Ionic crystal lattice
At the sites of the ionic lattice there are atoms connected by ionic bonds. This type of lattice is characteristic of substances that have ionic bonds: metal salts, oxides and hydroxides.
Associate this series of substances with table salt - NaCl. Substances with an ionic lattice have high melting and boiling points, are easily soluble in water, brittle, solid, their solutions and melts conduct electric current.
Examples: NaCl, MgCl2, NH4Br, KNO3, Li2O, Na3PO4.
Metal crystal lattice
The nodes of the metal lattice contain metal atoms. This type of lattice is characteristic of substances formed by a metallic bond.
Associate the properties of these substances with copper. They have a characteristic metallic luster, are malleable and ductile, conduct electricity and heat well, and have high melting and boiling points.
Examples: Cu, Fe, Zn, Al, Cr, Mn.
Atomic crystal lattice
At the sites of the atomic lattice there are atoms connected by covalent polar or nonpolar bonds.
Associate these substances with sand. They are very hard, very refractory (high melting point), non-volatile, durable, and insoluble in water.
Examples: SiO2, B, Ge, SiC, Al2O3. I would especially like to highlight: diamond and graphite (C), red and black phosphorus (P).
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Atomic lattice
Substances with an atomic crystal lattice, as a rule, have strong covalent bonds in their nodes consisting of atoms themselves. A covalent bond occurs when two identical atoms share fraternal electrons with each other, thus forming a common pair of electrons for neighboring atoms. Because of this, covalent bonds bind atoms tightly and evenly in a strict order - perhaps this is the most characteristic feature of the structure of the atomic crystal lattice. Chemical elements with similar bonds can boast of their hardness and high melting point. Chemical elements such as diamond, silicon, germanium, and boron have an atomic crystal lattice.
Molecular crystal lattice
The nodes of this structure contain molecules that are tightly packed together. Such substances are characterized by covalent polar and nonpolar bonds. It is interesting that, regardless of the covalent bond, there is a very weak attraction between the particles (due to weak van der Waals forces). That is why such substances are very fragile, have low boiling and melting points, and are also volatile. These substances include: water, organic substances (sugar, naphthalene), carbon monoxide (IV), hydrogen sulfide, noble gases, two- (hydrogen, oxygen, chlorine, nitrogen, iodine), three- (ozone), four- (phosphorus ), eight-atomic (sulfur) substances, and so on.
One of the distinctive features is that the structural and spatial model is preserved in all phases (both solid, liquid and gaseous).
Metal grate
The type of bond of a metal crystal lattice is more flexible and ductile than the ionic one, although in appearance they are very similar. Its distinctive feature is the presence of positively charged cations (metal ions) at lattice sites. Between the nodes live electrons that participate in the creation of the electric field; these electrons are also called electric gas. The presence of such a structure of a metal crystal lattice explains its properties: mechanical strength, heat and electrical conductivity, fusibility.
General structure
Metals are solid substances with a crystalline structure. The exception is mercury, a liquid metal. Crystal lattices are metal atoms ordered in a certain way. Each atom consists of a positively charged nucleus and several negatively charged electrons. Metal atoms don't have enough electrons, so they are ions.
A unit of a crystal lattice is an elementary crystal cell, in the conventional nodes and on the faces of which there are positively charged ions. They are held together by metallic bonds that arise due to the random movement of electrons separated from the atoms (due to which the atoms turned into ions).
Negatively charged electrons keep positively charged electrons at an equal distance, giving the crystal lattice the correct geometric shape.
Rice. 1. Metal connection diagram.
The free movement of electrons determines the electrical and thermal conductivity of metals.
Video
And finally, a detailed video explanation about the properties of crystal lattices.
Author: Pavel Chaika, editor-in-chief of Poznavaika magazine
When writing the article, I tried to make it as interesting, useful and high-quality as possible. I would be grateful for any feedback and constructive criticism in the form of comments on the article. You can also write your wish/question/suggestion to my email [email protected] or Facebook, with respect, the author.
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This article is available in English - Crystal Lattice in Chemistry.
Atomic crystal structure of metals
What is this structure, what is it characterized by? The name itself suggests that all metals are crystals in the solid state, that is, under normal conditions (except for mercury, which is a liquid). What is a crystal?
This is a conventional graphic image constructed by intersecting imaginary lines through the atoms that line up the body. In other words, every metal is made up of atoms. They are located in it not chaotically, but very correctly and consistently. So, if you mentally combine all these particles into one structure, you will get a beautiful image in the form of a regular geometric body of some shape.
This is what is commonly called the crystal lattice of a metal. It is very complex and spatially voluminous, therefore, for simplicity, not all of it is shown, but only a part, an elementary cell. A set of such cells, collected together and reflected in three-dimensional space, forms crystal lattices. Chemistry, physics and metallurgy are sciences that study the structural features of such structures.
The unit cell itself is a set of atoms that are located at a certain distance from each other and coordinate a strictly fixed number of other particles around themselves. It is characterized by packing density, distance between constituent structures, and coordination number. In general, all these parameters are characteristics of the entire crystal, and therefore reflect the properties exhibited by the metal.
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There are several types of crystal lattices. They all have one feature in common: the nodes contain atoms, and inside there is a cloud of electron gas, which is formed by the free movement of electrons inside the crystal.
Face-centered lattice
The crystal structure of metals having a face-centered cubic lattice is the following structure. This is a cube that includes fourteen atoms. Eight of them form lattice nodes, and another six are located, one on each face.
They have a similar structure:
The main distinctive properties are shine of different colors, lightness, strength, malleability, increased resistance to corrosion.
