Geological classification

Who is characterized by an ionic crystal lattice?

All molecules are made up of tiny particles called atoms. All currently discovered atoms are collected in the periodic table. Atom is the smallest, chemically indivisible particle of a substance that retains its chemical properties. Atoms connect with each other chemical bonds. Previously, we already looked at the types of chemical bonds and their properties. Be sure to study the theory on the topic: Types of Chemical Bonds before studying this article! Now let’s look at how particles in matter can connect. Depending on the location of the particles relative to each other, the properties of the substances they form can vary greatly. So, if the particles are located apart from each other long away (the distance between particles is much greater than the size of the particles themselves), practically do not interact with each other, move in space chaotically and continuously, then we are dealing with gas . If the particles are located close to each other, but chaotically, more interact with each other, make intense oscillatory movements in one position, but can jump to another position, then this is a model of the structure liquids . If the particles are located close to each other, but more in an orderly mannerand interact more each other, but move only within one equilibrium position, practically not moving to other positions, then we are dealing with solid . Most known chemical substances and mixtures can exist in solid, liquid and gaseous states. The simplest example is water. Under normal conditions it liquid, at 0 o C it freezes – goes from a liquid state to solid, and at 100 o C it boils – turns into gas phase – water vapor. Moreover, many substances under normal conditions are gases, liquids or solids. For example, air – a mixture of nitrogen and oxygen – is a gas under normal conditions. But at high pressure and low temperature, nitrogen and oxygen condense and pass into the liquid phase. Liquid nitrogen is actively used in industry. Sometimes isolated plasmaand liquid crystals, as separate phases. Many properties of individual substances and mixtures are explained mutual arrangement of particles in space relative to each other! This article examines properties of solids, depending on their structure. Basic physical properties of solids: melting point, electrical conductivity, thermal conductivity, mechanical strength, ductility, etc. Melting temperature – this is the temperature at which a substance passes from the solid phase to the liquid phase, and vice versa. Plastic is the ability of a substance to deform without destruction. Electrical Conductivity is the ability of a substance to conduct current. Current is the ordered movement of charged particles. Thus, current can only be carried out by substances that contain mobile charged particles. Based on their ability to conduct current, substances are divided into conductors and dielectrics. Conductors are substances that can conduct current (i.e. contain mobile charged particles). Dielectrics are substances that practically do not conduct current. In a solid substance, particles of a substance can be located chaoticallyor more orderlyO. If the particles of a solid substance are located in space chaotically, the substance is called amorphous . Examples of amorphous substances – coal, mica glass. If the particles of a solid substance are arranged in space in an orderly manner, i.e. form repeating three-dimensional geometric structures, such a substance is called crystal , and the structure itself – crystal lattice . Most of the substances we know are crystals. The particles themselves are located in nodes crystal lattice. Crystalline substances are distinguished, in particular, by type of chemical bond between particles in a crystal – atomic, molecular, metallic, ionic; according to the geometric shape of the simplest cell of a crystal lattice – cubic, hexagonal, etc. Depending on the type of particles that form a crystal lattice , distinguish atomic, molecular, ionic and metal crystal structure .

Atomic crystal lattice

An atomic crystal lattice is formed when the nodes of the crystal are located atoms . The atoms are strongly connected to each other covalent chemical bonds. Accordingly, such a crystal lattice will be very durable, it is not easy to destroy it. An atomic crystal lattice can be formed by atoms with high valency, i.e. with a large number of bonds with neighboring atoms (4 or more). As a rule, these are non-metals: simple substances – silicon, boron, carbon (allotropic modifications diamond, graphite), and their compounds (boron carbon, silicon oxide (IV), etc..). Since predominantly covalent chemical bonds occur between nonmetals, free electrons (like other charged particles) in substances with an atomic crystal lattice in most cases no. Therefore, such substances are usually conduct electricity very poorly, i.e. are dielectrics. These are general patterns, to which there are a number of exceptions. Communication between particles in atomic crystals: covalent polar or nonpolar. At the nodes of the crystal with an atomic crystal structure located atoms. Phase state atomic crystals under normal conditions: as a rule, solids. Substances , forming atomic crystals in the solid state:

  1. Simple substanceshigh valency (located in the middle of the periodic table): boron, carbon, silicon, etc.
  2. Complex substances formed by these non-metals: silica (silicon oxide, quartz sand) SiO2; silicon carbide (carborundum) SiC; boron carbide, boron nitride, etc.

Physical properties of substances with an atomic crystal lattice:


— refractoriness (high melting point);

— low electrical conductivity;

— low thermal conductivity;

— chemical inertness (inactive substances);

– insolubility in solvents.

Molecular crystal lattice

Molecular crystal lattice – this is a lattice, at the nodes of which there are molecules. Holds molecules in crystal weak forces of intermolecular attraction (van der Waals forces, hydrogen bonds, or electrostatic attraction). Accordingly, such a crystal lattice, as a rule, quite easy to destroy. Substances with a molecular crystal lattice – fusible, fragile. The greater the force of attraction between molecules, the higher the melting point of the substance. As a rule, the melting temperatures of substances with a molecular crystal lattice are not higher than 200-300K. Therefore, under normal conditions, most substances with a molecular crystal lattice exist in the form gases or liquids. The molecular crystal lattice, as a rule, is formed in solid form by acids, oxides of non-metals, other binary compounds of non-metals, simple substances that form stable molecules (oxygen O2, nitrogen N2, water H2O, etc.), organic substances. As a rule, these are substances with a covalent polar (less often nonpolar) bond. Because electrons are involved in chemical bonds, substances with a molecular crystal lattice – dielectrics, do not conduct heat well.

Communication between particles in molecular crystals: mintermolecular hydrogen bonds, electrostatic or intermolecular attractive forces.

At the nodes of the crystal with a molecular crystal structure located molecules.

Phase state molecular crystals under normal conditions: gases, liquids and solids.

Substances , forming in the solid state molecular crystals:

  1. Simple nonmetallic substances that form small, strong molecules(O2, N2, H2, S8 and others);
  2. Complex substances (non-metal compounds) with polar covalent bonds(except for silicon and boron oxides, silicon and carbon compounds) – water H2O, sulfur oxide SO3 and more
  3. Monatomic noble gases (helium, neon, argon, kryptonand etc.);
  4. Most organic substances that do not have ionic bondsmethane CH4, benzene C6Н6 and more

physical properties substances with a molecular crystal lattice:

— fusibility (low melting point):

— high compressibility;

— molecular crystals in solid form, as well as in solutions and melts, do not conduct current;

– phase state under normal conditions – gases, liquids, solids;

— high volatility;

– low hardness.

Ionic crystal lattice

If there are charged particles at the crystal nodes – ions, we can talk about ionic crystal lattice . Typically, ionic crystals alternate positive ions (cations) and negative ions (anions), so the particles are held in the crystal forces of electrostatic attraction . Depending on the type of crystal and the type of ions forming the crystal, such substances can be quite durable and refractory. In the solid state, there are usually no mobile charged particles in ionic crystals. But when the crystal dissolves or melts, the ions are released and can move under the influence of an external electric field. Those. Only solutions or melts conduct current ionic crystals. The ionic crystal lattice is characteristic of substances with ionic chemical bond. Examples such substances – salt NaCl, calcium carbonate – CaCO3 etc. An ionic crystal lattice, as a rule, is formed in the solid phase salts, bases, as well as metal oxides and binary compounds of metals and non-metals.

Communication between particles in ionic crystals: ionic chemical bond.

At the nodes of the crystal with an ionic lattice located ions.

Phase state ionic crystals under normal conditions: as a rule, solids.

Chemical substances with ionic crystal lattice:

  1. Salts (organic and inorganic), including ammonium salts (Eg, ammonium chloride NH4Cl);
  2. Grounds;
  3. Metal oxides;
  4. Binary compounds containing metals and non-metals.

Physical properties of substances with an ionic crystal structure:

— high melting point (refractoriness);

— solutions and melts of ionic crystals are current conductors;

— most compounds are soluble in polar solvents (water);

– solid phase state for most compounds under normal conditions.

Metal crystal lattice

And finally, metals are characterized by a special type of spatial structure – metal crystal lattice, which is due metal chemical bond . Metal atoms hold valence electrons rather weakly. In a crystal formed by a metal, the following processes occur simultaneously: Some atoms give up electrons and become positively charged ions; these electrons move randomly in the crystal; some electrons are attracted to ions. These processes occur simultaneously and chaotically. Thus, ions arise , as in the formation of an ionic bond, and shared electrons are formed , as in the formation of a covalent bond. Free electrons move randomly and continuously throughout the entire volume of the crystal, like a gas. That’s why they are sometimes called ” electron gas ” Due to the presence of a large number of mobile charged particles, metals conduct current and heat. The melting point of metals varies greatly. Metals are also characterized a peculiar metallic luster, malleability, i.e. the ability to change shape without destruction under strong mechanical stress, because chemical bonds are not destroyed.

Communication between particles : metal chemical bond.

At the nodes of the crystal with metal grille located metal ions and atoms.

Phase state metals under normal conditions: usually solids (exception is mercury, a liquid under normal conditions).

Chemical substances with a metal crystal lattice – simple substances – metals.

Physical properties of substances with a metal crystal lattice:

— high thermal and electrical conductivity;

— malleability and plasticity;

– metallic luster;

– metals are usually insoluble in solvents;

– Most metals are solids under normal conditions.

Comparison of the properties of substances with different crystal lattices

The type of crystal lattice (or lack of a crystal lattice) allows you to evaluate the basic physical properties of a substance. To roughly compare the typical physical properties of compounds with different crystal lattices, it is very convenient to use chemicals with characteristic properties. For a molecular lattice this is, for example, carbon dioxide, for an atomic crystal lattice – diamond, for metal – copper, and for the ionic crystal lattice – salt, sodium chloride NaCl.

Summary table on the structures of simple substances formed by chemical elements from the main subgroups of the periodic table (elements of the side subgroups are metals, therefore, have a metallic crystal lattice).

The final table of the relationship between the properties of substances and their structure:

Look at the snowflake. It has been proven that there are no two absolutely identical snowflakes in the world, despite the huge amount of snow. The crystal lattice is responsible for the shape, size and even the temperature at which a snowflake turns into a droplet of water.

The study of crystals has interested people since ancient times. There is even a special science about crystals – crystallography. It includes crystal chemistry and crystal physics. In 1749, M.V. Lomonosov formulated a hypothesis about the structure of crystalline bodies. R. J. Gayuy is the founder of the theory of the lattice structure of crystals, and O. Bravais studied various geometric shapes and structures of crystal lattices. With the discovery of X-rays, it was possible for the first time to “see” the structure of a beryl crystal.

What is a crystal lattice

As the name implies, the crystal lattice (CL) indicates that the substance in question is a crystal. A lattice is a collection of points called nodes and connected by conventional lines. At the nodes of a crystal lattice there can be various particles of a substance located at equal distances from each other. This structure can be expressed as an imaginary geometric image that allows for the alignment and parallel transfer of each crystal lattice.

Useful information about the crystal lattice

Coordination number KR The number of particles that are directly combined with the particle located in the CR node and have chemical bonds with it.
KR constant The minimum space between particles located at the nodes of the CR and having a chemical bond.
Symmetry KR Since the CR has a stable structure, it is able to maintain its identity when moving spatially.

Types of crystal lattices

In any crystal lattice there is an elementary cell, which is its smallest structural unit and has all the characteristics of its symmetry. Depending on which particles are located at the nodes of the crystal lattice and what the nature of the chemical bond is, atomic, molecular, ionic and metallic crystal lattice are distinguished.

Atomic crystal lattice

There are three main types of atomic crystal lattice:

At the nodes of such a crystal lattice there are atoms united by a covalent bond. These substances are characterized by strength, significant hardness, resistance to melting, and insolubility in the vast majority of solvents.

  1. layered form (for example, graphite). The atoms in such a lattice are combined into large molecules, located one below the other, like a layer cake;
  2. framework form (for example, diamond), where the carbon atoms form a lattice resembling a pyramid. This structure gives the substance special strength;
  3. chain form (for example, cinnabar HgS), where the collection of atoms forms long chains.

Molecular crystal lattice

At the nodal points of such a crystal lattice there are molecules united by weak chemical bonds. Because of this, molecular crystals have little hardness, are non-electrically conductive, are volatile and fusible substances (for example, ice), and do not dissolve in an aqueous environment.

Ionic crystal lattice

The structure of an ionic crystal lattice is represented by positive and negative ions at its nodes and interconnected forces of electrostatic attraction. This lattice is characteristic of most salts (for example, NaCl), alkalis (KOH), and metal oxides (CaO). Such compounds have hardness combined with brittleness, they are non-volatile and refractory, capable of dissolving in water, and conduct electric current.

Metal crystal lattice

Metals, as is known, are distinguished by a certain set of characteristic properties: they have high hardness combined with ductility, good malleability is complemented by a high melting point, they are excellent conductors of heat and electricity. All these qualities are associated with a specific crystal lattice, the nodes of which can contain both atoms and metal ions. A special feature is the presence of common electrons that move freely in the space of the crystal lattice.

Examples of crystal lattice

Most substances found in nature have a crystal structure based on one of four types of crystal lattice.

An atomic lattice is found, for example, in silicon (Si), boron (B), quartz (SiO2), Germany (Ge). Noble gases (He, Ne, Ar and others), oxygen (O2), iodine (I2), “dry ice” (СО2).

The ionic lattice is characteristic of oxides of most metals (MgO, CaO), alkalis (NaOH, KOH), salts (NaCl, KNO3).

Metals and their alloys have a metallic crystal lattice.

How to determine the crystal lattice

The type of crystal lattice inherent in a particular natural or artificially obtained substance is determined by the type of chemical bond in the compound.

If there is a chemical interaction of ions in a substance, then we can rightfully talk about a crystal lattice of the ionic type. A metallic bond clearly indicates a metallic crystal lattice.

The situation is more complicated with a covalent chemical bond, since it can be in both an atomic and molecular lattice. In this case, you need to look at such characteristics of the substance as strength, refractoriness, hardness, which differ in compounds that have a molecular and atomic crystal lattice.

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Properties of crystal lattices

The properties of the crystal lattice depend not only on the nature of the connection between different particles of the substance, but also on their relative position relative to each other. For example, in diamond crystals, carbon atoms are arranged symmetrically and are connected by covalent non-polar bonds, which gives the substance high strength. On the contrary, the crystal structure of graphite, also consisting of carbon atoms, forms flat hexagons connected to each other by weak intermolecular bonds.

Problems on the topic “Crystal lattice”

Test what you have learned or remembered about crystal lattices by answering three simple questions

1. Name the type of crystal lattice of calcium (Ca).

2. Which of the following characteristics applies to substances with an atomic crystal lattice?

a) fragile
b) refractory
c) dissolve in an aqueous environment
d) electrically conductive

3. What particles are located at the nodes of the graphite crystal lattice?

a) molecules
b) ions
c) atoms
d) atoms and ions

Answers to problems

Let’s check your answers.

1. Metal
2. b) refractory
3. c) atoms

3 chemistry topics that will be useful on the test

Is there a chemistry test coming soon? Check if all of these topics are familiar to you.

  1. How to use the periodic table
  2. What is valence
  3. Modern ideas about the structure of the atom

Popular questions and answers

Answered by Victoria Elesina, Candidate of Biological Sciences, teacher of chemistry at the educational center of the Andrei Melnichenko Foundation in Biysk:

How are the crystal lattice and the state of aggregation of substances related?

A solid substance definitely has a crystal lattice, but its type is different. For example, metals as solids have a metallic lattice type. But gas and liquid can also have a solid state, as can be seen from the reference values. For example, carbon dioxide, depending on pressure and temperature, can be in a gaseous, liquid or solid state. According to reference values, the boiling point of carbon dioxide is –56,6°C at a pressure of one atmosphere, and –78,5°C is the freezing point at a pressure of one atmosphere. Carbon dioxide in the solid state is dry ice. It has a molecular lattice type.

How do you understand that a substance has a crystal lattice?

If you answer the first question, you can answer this question: all substances in the solid state have a crystal lattice.

Why is the topic “Crystal Lattice” studied in 8th grade?

Different textbooks cover this topic at different times. The question is not in which class this happens. The question is after what topic this should be done. In my opinion, after the student has studied the state of aggregation, it is possible to explain how this state of aggregation is structured. However, it is precisely the type of crystal lattice that should be considered in detail after the topic “Electrical dissociation”, since the appearance of ions as such is studied in it.

Which USE task in chemistry tests knowledge of the crystal lattice?

In assignment 4. This is a specific question about crystal lattice and its type.

However, in tasks 6 and 7 (interaction of simple and complex substances) I also mention the type of crystal lattice.

In tasks 20 and 21 (electrolysis and hydrolysis) there is a connection between crystal lattices and processes.

Task 27 (thermal effect of the reaction) depends on the state of aggregation, and therefore on the crystal lattice.

Problem 30 (electrolytic dissociation) is also closely related to types of crystal lattices.

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