Solids usually have a crystalline structure. It is characterized by the correct arrangement of particles at strictly defined points in space. When these points are mentally connected by intersecting straight lines, a spatial frame is formed, which is called crystal lattice.
The points at which particles are located are called crystal lattice nodes. The nodes of an imaginary lattice can contain ions, atoms or molecules. They make oscillatory movements. With increasing temperature, the amplitude of oscillations increases, which manifests itself in the thermal expansion of bodies.
Depending on the type of particles and the nature of the connection between them, four types of crystal lattices are distinguished: ionic, atomic, molecular and metallic.
Crystal lattices consisting of ions are called ionic. They are formed by substances with ionic bonds. An example is a sodium chloride crystal, in which, as already noted, each sodium ion is surrounded by six chloride ions, and each chloride ion by six sodium ions. This arrangement corresponds to the most dense packing if the ions are represented as spheres located in the crystal. Very often, crystal lattices are depicted as shown in Fig., where only the relative positions of the particles are indicated, but not their sizes.
The number of nearest neighboring particles closely adjacent to a given particle in a crystal or in an individual molecule is called coordination number.
In the sodium chloride lattice, the coordination numbers of both ions are 6. So, in a sodium chloride crystal it is impossible to isolate individual salt molecules. There are none. The entire crystal should be considered as a giant macromolecule consisting of an equal number of Na + and Cl - ions, Na n Cl n, where n is a large number. The bonds between ions in such a crystal are very strong. Therefore, substances with an ionic lattice have a relatively high hardness. They are refractory and low-flying.
Melting of ionic crystals leads to disruption of the geometrically correct orientation of the ions relative to each other and a decrease in the strength of the bond between them. Therefore, their melts conduct electric current. Ionic compounds generally dissolve easily in liquids consisting of polar molecules, such as water.
Crystal lattices, in the nodes of which there are individual atoms, are called atomic. The atoms in such lattices are connected to each other by strong covalent bonds. An example is diamond, one of the modifications of carbon. Diamond is made up of carbon atoms, each of which is bonded to four neighboring atoms. Coordination number of carbon in diamond is 4 
. In the diamond lattice, as in the sodium chloride lattice, there are no molecules. The entire crystal should be considered as a giant molecule. The atomic crystal lattice is characteristic of solid boron, silicon, germanium and compounds of some elements with carbon and silicon.
Crystal lattices consisting of molecules (polar and non-polar) are called molecular.
Molecules in such lattices are connected to each other by relatively weak intermolecular forces. Therefore, substances with a molecular lattice have low hardness and low melting points, are insoluble or slightly soluble in water, and their solutions almost do not conduct electric current. The number of inorganic substances with a molecular lattice is small.
Examples of them are ice, solid carbon monoxide (IV) (“dry ice”), solid hydrogen halides, solid simple substances formed by one- (noble gases), two- (F 2, Cl 2, Br 2, I 2, H 2 , O 2 , N 2), three- (O 3), four- (P 4), eight- (S 8) atomic molecules. The molecular crystal lattice of iodine is shown in Fig. 
. Most crystalline organic compounds have a molecular lattice.
Most solids have crystalline structure, which is characterized strictly defined arrangement of particles. If you connect the particles with conventional lines, you get a spatial framework called crystal lattice. The points at which crystal particles are located are called lattice nodes. The nodes of an imaginary lattice may contain atoms, ions or molecules.
Depending on the nature of the particles located at the nodes and the nature of the connection between them, four types of crystal lattices are distinguished: ionic, metallic, atomic and molecular.
Ionic are called lattices in whose nodes there are ions.
They are formed by substances with ionic bonds. At the nodes of such a lattice there are positive and negative ions connected to each other by electrostatic interaction.
Ionic crystal lattices have salts, alkalis, active metal oxides. Ions can be simple or complex. For example, at the lattice sites of sodium chloride there are simple sodium ions Na and chlorine Cl − , and at the lattice sites of potassium sulfate simple potassium ions K and complex sulfate ions S O 4 2 − alternate.
The bonds between ions in such crystals are strong. Therefore, ionic substances are solid, refractory, non-volatile. Such substances are good dissolve in water.
Crystal lattice of sodium chloride
Sodium chloride crystal
Metal called lattices, which consist of positive ions and metal atoms and free electrons.
They are formed by substances with metallic bonds. At the nodes of a metal lattice there are atoms and ions (either atoms or ions, into which atoms easily turn, giving up their outer electrons for common use).
Such crystal lattices are characteristic of simple substances of metals and alloys.
The melting points of metals can be different (from \(–37\) °C for mercury to two to three thousand degrees). But all metals have a characteristic metallic shine, malleability, ductility, conduct electricity well and warmth.
Metal crystal lattice
Hardware
Atomic lattices are called crystal lattices, at the nodes of which there are individual atoms connected by covalent bonds.
Diamond has this type of lattice - one of the allotropic modifications of carbon. Substances with an atomic crystal lattice include graphite, silicon, boron and germanium, as well as complex substances, for example carborundum SiC and silica, quartz, rock crystal, sand, which include silicon oxide (\(IV\)) Si O 2.
Such substances are characterized high strength and hardness. Thus, diamond is the hardest natural substance. Substances with an atomic crystal lattice have very high melting points and boiling. For example, the melting point of silica is \(1728\) °C, while for graphite it is higher - \(4000\) °C. Atomic crystals are practically insoluble.
Diamond crystal lattice
Diamond
Molecular are called lattices, at the nodes of which there are molecules connected by weak intermolecular interactions.
Despite the fact that the atoms inside the molecules are connected by very strong covalent bonds, weak forces of intermolecular attraction act between the molecules themselves. Therefore, molecular crystals have low strength and hardness, low melting points and boiling. Many molecular substances are liquids and gases at room temperature. Such substances are volatile. For example, crystalline iodine and solid carbon monoxide (\(IV\)) (“dry ice”) evaporate without turning into a liquid state. Some molecular substances have smell .
This type of lattice has simple substances in a solid state of aggregation: noble gases with monatomic molecules (He, Ne, Ar, Kr, Xe, Rn ), as well as non-metals with two- and polyatomic molecules (H 2, O 2, N 2, Cl 2, I 2, O 3, P 4, S 8).
They have a molecular crystal lattice also substances with covalent polar bonds: water - ice, solid ammonia, acids, non-metal oxides. Majority organic compounds are also molecular crystals (naphthalene, sugar, glucose).
Instructions
As you can easily guess from the name itself, the metal type of lattice is found in metals. These substances are usually characterized by a high melting point, metallic luster, hardness, and are good conductors of electric current. Remember that lattice sites of this type contain either neutral atoms or positively charged ions. In the spaces between the nodes there are electrons, the migration of which ensures the high electrical conductivity of such substances.
Ionic type of crystal lattice. It should be remembered that it is also inherent in salts. Characteristic - crystals of the well-known table salt, sodium chloride. Positively and negatively charged ions alternate alternately at the sites of such lattices. Such substances are usually refractory and have low volatility. As you might guess, they are of the ionic type.
The atomic type of crystal lattice is inherent in simple substances - nonmetals, which under normal conditions are solids. For example, sulfur, phosphorus,... At the sites of such lattices there are neutral atoms connected to each other by covalent chemical bonds. Such substances are characterized by refractoriness and insolubility in water. Some (for example, carbon in the form) have exceptionally high hardness.
Finally, the last type of lattice is molecular. It is found in substances that are under normal conditions in liquid or gaseous form. As again can be easily understood from, at the nodes of such lattices there are molecules. They can be either non-polar (for simple gases such as Cl2, O2) or polar (the most famous example is water H2O). Substances with this type of lattice do not conduct current, are volatile, and have low melting points.
Sources:
- grating type
Temperature melting of a solid is measured to determine its purity. Impurities in a pure substance usually lower the temperature melting or increase the interval over which the compound melts. The capillary method is a classic method for controlling impurities.
You will need
- - test substance;
- - glass capillary, sealed at one end (diameter 1 mm);
- - glass tube with a diameter of 6-8 mm and a length of at least 50 cm;
- - heated block.
Instructions
Place the glass tube vertically on a hard surface and drop the capillary through it several times, sealed end down. This helps compact the substance. To determine the temperature, the column of the substance in the capillary must be about 2-5 mm.
Place the capillary thermometer in the heated block and observe the changes in the test substance as the temperature increases. Before and during heating, the thermometer should not touch the walls of the block or other very hot surfaces, otherwise it may burst.
Note the temperature at which the first drops appear in the capillary (beginning melting), and the temperature at which the last substances disappear (end melting). In this interval, the substance begins to decrease until it completely transforms into a liquid state. When performing the analysis, also look for changes or decomposition of the substance.
Repeat measurements 1-2 more times. Present the results of each measurement in the form of the corresponding temperature interval during which the substance passes from solid to liquid. At the end of the analysis, make a conclusion about the purity of the test substance.
Video on the topic
In crystals, chemical particles (molecules, atoms and ions) are arranged in a certain order; under certain conditions they form regular symmetrical polyhedra. There are four types of crystal lattices - ionic, atomic, molecular and metallic.
Crystals
The crystalline state is characterized by the presence of long-range order in the arrangement of particles, as well as the symmetry of the crystal lattice. Solid crystals are three-dimensional formations in which the same structural element is repeated in all directions.
The correct shape of crystals is determined by their internal structure. If you replace molecules, atoms and ions in them with points instead of the centers of gravity of these particles, you get a three-dimensional regular distribution - . The repeating elements of its structure are called elementary cells, and the points are called nodes of the crystal lattice. There are several types of crystals depending on the particles that form them, as well as the nature of the chemical bond between them.
Ionic crystal lattices
Ionic crystals form anions and cations, between which there are. This type of crystal includes salts of most metals. Each cation is attracted to the anion and repelled by other cations, so it is impossible to isolate single molecules in an ionic crystal. The crystal can be considered as one huge one, and its size is not limited; it is capable of attaching new ions.
Atomic crystal lattices
In atomic crystals, individual atoms are united by covalent bonds. Like ionic crystals, they can also be thought of as huge molecules. At the same time, atomic crystals are very hard and durable, and do not conduct electricity and heat well. They are practically insoluble and are characterized by low reactivity. Substances with atomic lattices melt at very high temperatures.
Molecular crystals
Molecular crystal lattices are formed from molecules whose atoms are united by covalent bonds. Because of this, weak molecular forces act between molecules. Such crystals are characterized by low hardness, low melting point and high fluidity. The substances that they form, as well as their melts and solutions, do not conduct electric current well.
Metal crystal lattices
In metal crystal lattices, atoms are arranged with maximum density, their bonds are delocalized, and they extend throughout the entire crystal. Such crystals are opaque, have a metallic luster, are easily deformed, and are good conductors of electricity and heat.
This classification describes only limiting cases; most crystals of inorganic substances belong to intermediate types - molecular-covalent, covalent, etc. An example is a graphite crystal, inside each layer it has covalent-metallic bonds, and between the layers there are molecular ones.
Sources:
- alhimik.ru, Solids
Diamond is a mineral that belongs to one of the allotropic modifications of carbon. Its distinctive feature is its high hardness, which rightfully earns it the title of the hardest substance. Diamond is a fairly rare mineral, but at the same time it is the most widespread. Its exceptional hardness finds its application in mechanical engineering and industry.
Instructions
Diamond has an atomic crystal lattice. The carbon atoms that form the basis of the molecule are arranged in the form of a tetrahedron, which is why diamond has such high strength. All atoms are connected by strong covalent bonds, which are formed based on the electronic structure of the molecule.
The carbon atom has sp3 hybridized orbitals that are at an angle of 109 degrees and 28 minutes. The overlap of hybrid orbitals occurs in a straight line in the horizontal plane.
Thus, when the orbitals overlap at such an angle, a centered one is formed, which belongs to the cubic system, so we can say that diamond has a cubic structure. This structure is considered one of the strongest in nature. All tetrahedra form a three-dimensional network of layers of six-membered rings of atoms. Such a stable network of covalent bonds and their three-dimensional distribution leads to additional strength of the crystal lattice.
Structure of matter.
It is not individual atoms or molecules that enter into chemical interactions, but substances.
Our task is to get acquainted with the structure of matter.
At low temperatures, substances are in a stable solid state.
☼ The hardest substance in nature is diamond. He is considered the king of all gems and precious stones. And its name itself means “indestructible” in Greek. Diamonds have long been looked upon as miraculous stones. It was believed that a person wearing diamonds does not know stomach diseases, is not affected by poison, retains his memory and a cheerful mood until old age, and enjoys royal favor.
☼ A diamond that has been subjected to jewelry processing - cutting, polishing - is called a diamond.
When melting, as a result of thermal vibrations, the order of the particles is disrupted, they become mobile, while the nature of the chemical bond is not disrupted. Thus, there are no fundamental differences between solid and liquid states.
The liquid acquires fluidity (i.e., the ability to take the shape of a vessel).
Liquid crystals.
Liquid crystals were discovered at the end of the 19th century, but have been studied in the last 20-25 years. Many display devices of modern technology, for example, some electronic watches and mini-computers, operate on liquid crystals.
In general, the words “liquid crystals” sound no less unusual than “hot ice”. However, in reality, ice can also be hot, because... at a pressure of more than 10,000 atm. water ice melts at temperatures above 2000 C. The unusualness of the combination “liquid crystals” is that the liquid state indicates the mobility of the structure, and the crystal implies strict order.
If a substance consists of polyatomic molecules of an elongated or lamellar shape and having an asymmetrical structure, then when it melts, these molecules are oriented in a certain way relative to each other (their long axes are parallel). In this case, the molecules can move freely parallel to themselves, i.e. the system acquires the property of fluidity characteristic of a liquid. At the same time, the system retains an ordered structure, which determines the properties characteristic of crystals.
The high mobility of such a structure makes it possible to control it through very weak influences (thermal, electrical, etc.), i.e. purposefully change the properties of a substance, including optical ones, with very little energy expenditure, which is what is used in modern technology.
Types of crystal lattices.
Any chemical substance is formed by a large number of identical particles that are interconnected.
At low temperatures, when thermal movement is difficult, the particles are strictly oriented in space and form a crystal lattice.
Crystal lattice is a structure with a geometrically correct arrangement of particles in space.
In the crystal lattice itself, nodes and internodal space are distinguished.
The same substance, depending on conditions (p, t,...), exists in different crystalline forms (i.e., they have different crystal lattices) - allotropic modifications that differ in properties.
For example, four modifications of carbon are known: graphite, diamond, carbyne and lonsdaleite.
☼ The fourth variety of crystalline carbon, “lonsdaleite,” is little known. It was discovered in meteorites and obtained artificially, and its structure is still being studied.
☼ Soot, coke, and charcoal were classified as amorphous polymers of carbon. However, it has now become known that these are also crystalline substances.
☼ By the way, shiny black particles were found in the soot, which were called “mirror carbon”. Mirror carbon is chemically inert, heat-resistant, impermeable to gases and liquids, has a smooth surface and is absolutely compatible with living tissues.
☼ The name graphite comes from the Italian “graffito” - I write, I draw. Graphite is dark gray crystals with a weak metallic luster and has a layered lattice. Individual layers of atoms in a graphite crystal, connected to each other relatively weakly, are easily separated from each other.
TYPES OF CRYSTAL LATTICES
Properties of substances with different crystal lattices (table)
If the rate of crystal growth is low upon cooling, a glassy state (amorphous) is formed.
The relationship between the position of an element in the Periodic Table and the crystal lattice of its simple substance.
There is a close relationship between the position of an element in the periodic table and the crystal lattice of its corresponding elemental substance.
The simple substances of the remaining elements have a metallic crystal lattice.
FIXING
Study the lecture material and answer the following questions in writing in your notebook:
- What is a crystal lattice?
- What types of crystal lattices exist?
- Describe each type of crystal lattice according to the plan:
What is in the nodes of the crystal lattice, structural unit → Type of chemical bond between the particles of the node → Interaction forces between the particles of the crystal → Physical properties determined by the crystal lattice → Aggregate state of the substance under normal conditions → Examples
Complete tasks on this topic:
- What type of crystal lattice does the following substances widely used in everyday life have: water, acetic acid (CH3 COOH), sugar (C12 H22 O11), potassium fertilizer (KCl), river sand (SiO2) - melting point 1710 0C, ammonia (NH3) , table salt? Make a general conclusion: by what properties of a substance can one determine the type of its crystal lattice?
Using the formulas of the given substances: SiC, CS2, NaBr, C2 H2 - determine the type of crystal lattice (ionic, molecular) of each compound and, based on this, describe the physical properties of each of the four substances.
Trainer No. 1. "Crystal lattices"
Trainer No. 2. "Test tasks"
Test (self-control):
1) Substances that have a molecular crystal lattice, as a rule:
a). refractory and highly soluble in water
b). fusible and volatile
V). Solid and electrically conductive
G). Thermally conductive and plastic
2) The concept of “molecule” is not applicable to the structural unit of a substance:
b). oxygen
V). diamond
3) The atomic crystal lattice is characteristic of:
a). aluminum and graphite
b). sulfur and iodine
V). silicon oxide and sodium chloride
G). diamond and boron
4) If a substance is highly soluble in water, has a high melting point, and is electrically conductive, then its crystal lattice is:
A). molecular
b). atomic
V). ionic
G). metal
Molecular and non-molecular structure of substances. Structure of matter
It is not individual atoms or molecules that enter into chemical interactions, but substances. Substances are classified according to the type of bond molecular And non-molecular structure. Substances made up of molecules are called molecular substances. The bonds between molecules in such substances are very weak, much weaker than between atoms inside the molecule, and even at relatively low temperatures they break - the substance turns into a liquid and then into a gas (sublimation of iodine). The melting and boiling points of substances consisting of molecules increase with increasing molecular weight. TO molecular substances include substances with an atomic structure (C, Si, Li, Na, K, Cu, Fe, W), among them there are metals and non-metals. To substances non-molecular structure include ionic compounds. Most compounds of metals with non-metals have this structure: all salts (NaCl, K 2 SO 4), some hydrides (LiH) and oxides (CaO, MgO, FeO), bases (NaOH, KOH). Ionic (non-molecular) substances have high melting and boiling points.
Solids: amorphous and crystalline
Solids are divided into crystalline and amorphous.
Amorphous substances they do not have a clear melting point - when heated, they gradually soften and turn into a fluid state. For example, plasticine and various resins are in an amorphous state.
Crystalline substances characterized by the correct arrangement of the particles of which they consist: atoms, molecules and ions - at strictly defined points in space. When these points are connected by straight lines, a spatial framework is formed, called a crystal lattice. The points at which crystal particles are located are called lattice nodes. Depending on the type of particles located at the nodes of the crystal lattice and the nature of the connection between them, four types of crystal lattices are distinguished: ionic, atomic, molecular and metallic.
Crystal lattices are called ionic, at the nodes of which there are ions. They are formed by substances with ionic bonds, which can bind both simple ions Na+, Cl -, and complex SO 4 2-, OH -. Consequently, salts and some oxides and hydroxides of metals have ionic crystal lattices. For example, a sodium chloride crystal is built from alternating positive Na + and negative Cl - ions, forming a cube-shaped lattice. The bonds between ions in such a crystal are very stable. Therefore, substances with an ionic lattice are characterized by relatively high hardness and strength, they are refractory and non-volatile.
Crystalline lattice - a) and amorphous lattice - b).
Crystalline lattice - a) and amorphous lattice - b). Atomic crystal lattices
Atomic are called crystal lattices, in the nodes of which there are individual atoms. In such lattices the atoms are connected to each other very strong covalent bonds. An example of substances with this type of crystal lattices is diamond, one of the allotropic modifications of carbon. Most substances with an atomic crystal lattice have very high melting points (for example, for diamond it is over 3500 ° C), they are strong and hard, and practically insoluble.
Molecular crystal lattices
Molecular called crystal lattices, in the nodes of which molecules are located. Chemical bonds in these molecules can be both polar (HCl, H 2 O) and non-polar (N 2, O 2). Despite the fact that the atoms inside the molecules are connected by very strong covalent bonds, weak forces of intermolecular attraction act between the molecules themselves. Therefore, substances with molecular crystal lattices have low hardness, low melting points, and are volatile. Most solid organic compounds have molecular crystal lattices (naphthalene, glucose, sugar).
Molecular crystal lattice(carbon dioxide) Metal crystal lattices
Substances with metal bond have metal crystal lattices. At the nodes of such lattices there are atoms and ions(either atoms or ions into which metal atoms easily transform, giving up their outer electrons “for common use”). This internal structure of metals determines their characteristic physical properties: malleability, ductility, electrical and thermal conductivity, characteristic metallic luster.
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