As we already know, matter can exist in three states of aggregation: gaseous, solid And liquid. Oxygen, which under normal conditions is in a gaseous state, at a temperature of -194 ° C is converted into a bluish liquid, and at a temperature of -218.8 ° C it turns into a snowy mass with blue crystals.
The temperature interval for the existence of a substance in the solid state is determined by the boiling and melting points. Solids are crystalline And amorphous.
At amorphous substances there is no fixed melting point - when heated, they gradually soften and become fluid. In this state, for example, there are various resins, plasticine.
Crystalline substances differ in the regular arrangement of the particles of which they are composed: atoms, molecules and ions, at strictly defined points in space. When these points are connected by straight lines, a spatial frame is created, it is called a crystal lattice. The points where the crystal particles are located are called lattice nodes.
At the nodes of the lattice we imagine, there can be ions, atoms and molecules. These particles oscillate. When the temperature increases, the scope of these fluctuations also increases, which leads to thermal expansion of the bodies.
Depending on the type of particles located in 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 metal.
Ionic called such crystal lattices, at the nodes of which ions are located. They are formed by substances with an ionic bond, which can be associated with both simple ions Na +, Cl-, and complex SO24-, OH-. Thus, ionic crystal lattices have salts, some oxides and hydroxyls of metals, i.e. those substances in which there is an ionic chemical bond. Let's consider a crystal of sodium chloride, it consists of positively alternating Na+ and negative CL- ions, together they form a lattice in the form of a cube. The bonds between ions in such a crystal are extremely stable. Because of this, substances with an ionic lattice have a relatively high strength and hardness, they are refractory and non-volatile.
nuclear crystal lattices are called such crystal lattices, at the nodes of which there are individual atoms. In such lattices, atoms are interconnected by very strong covalent bonds. For example, diamond is one of the allotropic modifications of carbon.
Substances with an atomic crystal lattice are not very common in nature. These include crystalline boron, silicon and germanium, as well as complex substances, for example, those that contain silicon oxide (IV) - SiO 2: silica, quartz, sand, rock crystal.
The vast majority of substances with an atomic crystal lattice have very high melting points (for diamond it exceeds 3500 ° C), such substances are strong and hard, practically insoluble.
Molecular called such crystal lattices, at the nodes of which molecules are located. Chemical bonds in these molecules can also be either polar (HCl, H 2 0) or non-polar (N 2 , O 3). And although the atoms inside the molecules are connected by very strong covalent bonds, weak forces of intermolecular attraction act between the molecules themselves. That is why substances with molecular crystal lattices are characterized by low hardness, low melting point, and volatility.
Examples of such substances are solid water - ice, solid carbon monoxide (IV) - "dry ice", solid hydrogen chloride and hydrogen sulfide, solid simple substances formed by one - (noble gases), two - (H 2, O 2, CL 2 , N 2, I 2), three - (O 3), four - (P 4), eight-atomic (S 8) molecules. The vast majority of solid organic compounds have molecular crystal lattices (naphthalene, glucose, sugar).
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Molecular and non-molecular structure of substances. The structure of matter
It is not individual atoms or molecules that enter into chemical interactions, but substances. Substances are distinguished by 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 a molecule, and already at relatively low temperatures they break - the substance turns into a liquid and then into a gas (iodine sublimation). 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 do not have a clear melting point - when heated, they gradually soften and become fluid. In the amorphous state, for example, are plasticine and various resins.
Crystalline substances are characterized by the correct arrangement of the particles of which they are composed: atoms, molecules and ions - at strictly defined points in space. When these points are connected by straight lines, a spatial frame is formed, called the 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 sites of which there are ions. They are formed by substances with an ionic bond, which can be associated with both simple ions Na +, Cl -, and complex SO 4 2-, OH -. Consequently, salts, 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.
Crystal lattice - a) and amorphous lattice - b).
Crystal lattice - a) and amorphous lattice - b). Atomic crystal lattices
nuclear called crystal lattices, in the nodes of which there are individual atoms. In such lattices, atoms are connected to each other very strong covalent bonds. An example of substances with this type of crystal lattice is diamond, one of the allotropic modifications of carbon. Most substances with an atomic crystal lattice have very high melting points (for example, in diamond it is over 3500 ° C), they are strong and hard, practically insoluble.
Molecular crystal lattices
Molecular called crystal lattices, at 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 atoms within molecules are bound 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) Metallic crystal lattices
Substances with metallic bond have metallic crystal lattices. At the nodes of such lattices are atoms and ions(either atoms, or ions, into which metal atoms easily turn, giving their outer electrons “for general use”). Such an internal structure of metals determines their characteristic physical properties: malleability, plasticity, electrical and thermal conductivity, and a characteristic metallic luster.
cheat sheets
In solids, particles (molecules, atoms, and ions) are located so close to each other that the forces of interaction between them do not allow them to fly apart. These particles can only make oscillatory motions around the equilibrium position. Therefore, solid bodies retain their shape and volume.
According to their molecular structure, solids are divided into crystalline And amorphous .
The structure of crystalline bodies
Crystal cell
Such solids are called crystalline, in which molecules, atoms or ions are arranged in a strictly defined geometric order, forming a structure in space, which is called crystal lattice . This order is periodically repeated in all directions in three-dimensional space. It persists over long distances and is not limited in space. He is called long-range order .
Types of crystal lattices
A crystal lattice is a mathematical model that can be used to represent how particles are arranged in a crystal. Mentally connecting in space with straight lines the points where these particles are located, we will get a crystal lattice.
The distance between atoms located at the nodes of this lattice is called lattice parameter .
Depending on which particles are located at the nodes, crystal lattices are molecular, atomic, ionic and metallic .
Such properties of crystalline bodies as melting point, elasticity, and strength depend on the type of crystal lattice.
When the temperature rises to a value at which the melting of the solid begins, the crystal lattice is destroyed. Molecules get more freedom, and the solid crystalline substance passes into the liquid stage. The stronger the bonds between molecules, the higher the melting point.
molecular lattice
In molecular lattices, bonds between molecules are not strong. Therefore, under normal conditions, such substances are in a liquid or gaseous state. The solid state for them is possible only at low temperatures. Their melting point (transition from solid to liquid) is also low. And under normal conditions, they are in a gaseous state. Examples are iodine (I 2), "dry ice" (carbon dioxide CO 2).
atomic lattice
In substances that have an atomic crystal lattice, the bonds between atoms are strong. Therefore, the substances themselves are very solid. They melt at high temperatures. Silicon, germanium, boron, quartz, oxides of some metals, and the hardest substance in nature, diamond, have a crystalline atomic lattice.
Ionic lattice
Substances with an ionic crystal lattice include alkalis, most salts, oxides of typical metals. Since the attractive force of ions is very high, these substances can only melt at very high temperatures. They are called refractory. They have high strength and hardness.
metal grate
At the nodes of the metal lattice, which all metals and their alloys have, both atoms and ions are located. Due to this structure, metals have good malleability and ductility, high thermal and electrical conductivity.
Most often, the shape of the crystal is a regular polyhedron. The faces and edges of such polyhedra always remain constant for a particular substance.
A single crystal is called single crystal . It has a regular geometric shape, a continuous crystal lattice.
Examples of natural single crystals are diamond, ruby, rock crystal, rock salt, Icelandic spar, quartz. Under artificial conditions, single crystals are obtained in the process of crystallization, when solutions or melts are cooled to a certain temperature and a solid substance in the form of crystals is isolated from them. With a slow crystallization rate, the faceting of such crystals has a natural shape. In this way, under special industrial conditions, for example, single crystals of semiconductors or dielectrics are obtained.
Small crystals, randomly fused with each other, are called polycrystals . The clearest example of a polycrystal is granite. All metals are also polycrystals.
Anisotropy of crystalline bodies
In crystals, particles are located with different densities in different directions. If we connect atoms in a straight line in one of the directions of the crystal lattice, then the distance between them will be the same in all this direction. In any other direction, the distance between the atoms is also constant, but its value may already differ from the distance in the previous case. This means that interaction forces of different magnitude act between atoms in different directions. Therefore, the physical properties of matter in these directions will also differ. This phenomenon is called anisotropy - the dependence of the properties of matter on direction.
Electrical conductivity, thermal conductivity, elasticity, refractive index and other properties of a crystalline substance differ depending on the direction in the crystal. Electric current is conducted differently in different directions, matter is heated differently, light rays are refracted differently.
Anisotropy is not observed in polycrystals. The properties of matter remain the same in all directions.
Instruction
As you can easily guess from the name itself, the metallic type of lattice is found in metals. These substances are characterized, as a rule, by a high melting point, metallic luster, hardness, and are good conductors of electric current. Remember that at the sites of this type of lattice there are either neutral atoms or positively charged ions. In the gaps 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. At the nodes of such lattices, positively and negatively charged ions alternate alternately. Such substances, as a rule, are refractory, with low volatility. As you might guess, they are of the ionic type.
The atomic type of the crystal lattice is inherent in simple substances - non-metals, which under normal conditions are solids. For example, sulfur, phosphorus,. At the sites of such lattices there are neutral atoms bound to each other by a covalent chemical bond. Such substances are characterized by infusibility, insolubility in water. Some (for example, carbon in the form) - exceptionally high hardness.
Finally, the last type of lattice is molecular. It occurs in substances that are under normal conditions in liquid or gaseous form. As again, it 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:
- lattice type
Temperature melting the solid is measured to determine its degree of purity. Impurities in a pure substance usually lower the temperature melting or increase the interval in which the compound melts. The capillary method is the classic method for monitoring impurities.
You will need
- - test substance;
- - glass capillary sealed at one end (diameter 1 mm);
- - a glass tube with a diameter of 6-8 mm and a length of at least 50 cm;
- - heated block.
Instruction
Pound the pre-dried test subject in a mortar into the smallest. Carefully take the capillary and immerse the open end into the substance, while some of it should fall into the capillary.
Stand the glass tube vertically on a hard surface and drop the capillary through it several times with the sealed end down. This contributes to the compaction of the substance. To determine the temperature, the column of the substance in the capillary should be about 2-5 mm.
Place the capillary thermometer in the heated block and observe the change in the test substance as the temperature rises. The thermometer before and during heating should not touch the walls of the block and other strongly heated 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 subside until the complete transition to the liquid state. When analyzing, also pay attention to the change 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 a solid to a liquid state. At the end of the analysis, make a conclusion about the purity of the test substance.
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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 by the symmetry of the crystal lattice. Solid crystals are called three-dimensional formations in which the same structural element is repeated in all directions.
The correct shape of crystals is due to their internal structure. If we replace molecules, atoms and ions in them with points instead of the centers of gravity of these particles, we get a three-dimensional regular distribution - . The repeating elements of its structure are called elementary cells, and the points are called the nodes of the crystal lattice. There are several types of crystals depending on the particles that form them, as well as on the nature of the chemical bond between them.
Ionic crystal lattices
Ionic crystals form anions and cations, between which there is. This type of crystals 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 able to attach new ions.
Atomic crystal lattices
In atomic crystals, individual atoms are united by covalent bonds. Like ionic crystals, they can also be viewed as huge molecules. At the same time, atomic crystals are very hard and durable, they do not conduct electricity and heat well. They are practically insoluble, they are characterized by low reactivity. Substances with atomic lattices melt at very high temperatures.
molecular crystals
Molecular crystal lattices are formed from molecules, the atoms of which are united by covalent bonds. Because of this, weak molecular forces act between the molecules. Such crystals are characterized by low hardness, low melting point and high fluidity. The substances they form, as well as their melts and solutions, are poor conductors of electric current.
Metallic crystal lattices
In the crystal lattices of metals, atoms are located with a maximum density, their bonds are delocalized, they extend to the entire crystal. Such crystals are opaque, have a metallic luster, are easily deformed, and conduct electricity and heat well.
This classification describes only extreme cases, most of the crystals of inorganic substances belong to intermediate types - molecular-covalent, covalent, etc. An example is a graphite crystal, inside each layer it has covalent-metal bonds, and between layers - molecular.
Sources:
- alhimik.ru, Solids
Diamond is a mineral belonging 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 the most widespread. Its exceptional hardness finds its application in mechanical engineering and industry.
Instruction
Diamond has an atomic crystal lattice. The carbon atoms that make up the basis of the molecule are arranged in the form of a tetrahedron, which is why the diamond has such a 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 hybridization of orbitals, which are located 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
Since ancient times, metals have played a huge role in the development of mankind. Their introduction into everyday life has made a real revolution both in the ways of processing materials and in human perception of the surrounding reality. Modern industry and agriculture, transport and infrastructure are impossible without the use of metals, the use of their useful qualities and properties. These qualities, in turn, are determined by the internal structure of this class of chemical compounds, which is based on the crystal lattice.
The concept and essence of the crystal lattice
From the point of view of the internal structure, any substance can be in one of three states - liquid, gaseous and solid. Moreover, it is the latter that is characterized by the greatest stability, due to the fact that the crystal lattice implies not only a clear arrangement of atoms or molecules in strictly defined places, but also the need to apply a sufficiently large force to break the bonds between these elementary particles.
Features of the ionic lattice
The structure of any substance in the solid state necessarily implies the periodic repetition of molecules and atoms in three dimensions at once. In this case, depending on what is at the key points, the crystal lattice can be ionic, atomic, molecular and metallic. As for the first variety, here the basic components are charged ions of opposite polarity, between which the so-called Coulomb forces arise and act. In this case, the interaction force is directly dependent on the radii of charged particles.
Such a lattice is a complex system consisting of metal cations, in the space between which negatively charged electrons move. It is the presence of these elementary particles that gives the lattice stability and hardness, because they serve as a kind of compensators for positively charged cations.
Strength and weakness of the atomic lattice
Quite interesting from the point of view of the structure is the atomic crystal lattice. Already from the name, we can conclude that atoms are located in its nodes, held by covalent bonds. In recent years, many scientists have attributed this type of interaction to the family of inorganic polymers, since the structure of this molecule is largely determined by the valency of its constituent atoms.
Main characteristics of the molecular lattice
The molecular crystal lattice is the least stable of all presented. The thing is that the level of interaction of the molecules located in its nodes is extremely low, and the energy potential is determined by a number of factors, in which the main role is played by dispersion, induction and orientation forces.
Influence of the crystal lattice on the properties of objects
Thus, the crystal lattice largely determines the properties of a substance. For example, atomic crystals melt at extremely high temperatures and have increased hardness, while substances with a metallic lattice are excellent conductors.
