“Crystal lattice” - Task: Determine the type of chemical bond in these compounds: Classification of solids. Characteristics of the main types of crystal lattices. The topic of the lesson is CRYSTAL LATTICES. HCl, Cl2, H2O, NaBr, BaCl2, CaS, O2, NH3, CO2, C.
“Crystal lattices chemistry” - Types of crystal lattices. Substances with ACR have high melting points and increased hardness. The placement points of particles are called crystal lattice nodes. The crystal lattice of a diamond is shown above. Evaluating your own progress. Law of constancy of composition. Atomic. Ionic crystal lattices are those whose nodes contain ions.
“Crystalline and amorphous substances” - Sulfur S8. Iodine I2. Solid. Examples: simple substances (H2, N2, O2, F2, P4, S8, Ne, He), complex substances(CO2, H2O, sugar C12H22O11, etc.). The state of aggregation of a substance (using the example of oxygen O2). There is no strict arrangement of particles, no crystal lattice. Properties of substances: 1) metallic luster, 2) thermal and electrical conductivity, 3) malleability and ductility, 4) opacity.
Polycrystal of amethyst (a type of quartz). Amorphous bodies. Lollipop. Properties solids. Amber. Druse of rock crystal crystals. Crystals. Polycrystalline metal. Monocrystal Rock salt. Druze Marion. Spar monocrystal. Amorphous body. Single crystal of rock crystal. Physical properties of amorphous bodies: 1. Shapeless 2. Absence of a melting point 3. Isotropy.
“Crystalline and amorphous bodies” - Purpose: to identify differences in the properties of crystals and amorphous bodies. Crystals have a melting point amorphous bodies– temperature range (fluidity). Equipment: magnifying glass, collection of minerals and rocks, metal collection. Polycrystals are isotropic. Crystals are anisotropic, amorphous bodies are isotropic. Availability constant temperature melting.
“Salt 4life” - Marbelle 750g. Zimushka-krasa 750g. 4life 125g. Prerequisites. Droga 1000g. Sea salt 4Life has unique taste properties. Assortment. What are the benefits of 4Life salt? Positioning. Marcel (package 1000g). Positioning map (tubes-salt shakers). Target Audience. Price, rub. Extra 1000g.
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 thermal expansion tel.
Depending on the type of particles and the nature of the connection between them, 4 types of crystal lattices are distinguished: ionic (NaCl, KCl), 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 each sodium ion is surrounded by 6 chloride ions, and each chloride ion is surrounded by 6 sodium ions.
NaCl crystal lattice
The number of nearest neighboring particles closely adjacent to a given particle in a crystal or individual molecule is called focal number.
In the NaCl lattice, the coordination numbers of both ions are equal to 6. And so, in a NaCl crystal it is impossible to isolate individual salt molecules. There are none. The entire crystal should be considered as a giant macromolecule consisting of equal number ions Na + and Cl -, 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, as a rule, easily dissolve in liquids consisting of polar molecules, such as water.
Crystal lattices, at 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 4 neighboring atoms. The coordination number of carbon in diamond is 4. Substances with an atomic crystal lattice have high temperature melting point (for diamond over 3500 o C), strong and hard, practically insoluble in water.
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 a low melting point, are insoluble or slightly soluble in water, and their solutions almost do not conduct electric current. Examples of them are ice, solid CO 2 (“dry ice”), halogens, crystals of hydrogen, oxygen, nitrogen, noble gases, etc.
Valence
An important quantitative characteristic showing the number of atoms interacting with each other in the resulting molecule is valence– the property of atoms of one element to join certain number atoms of other elements.
Valency is quantitatively determined by the number of hydrogen atoms, which this element can add or replace. So, for example, in hydrofluoric acid(HF) fluorine is monovalent, in ammonia (NH 3) nitrogen is trivalent, in hydrogen silicon (SiH 4 - silane) silicon is tetravalent, etc.
Later, with the development of ideas about the structure of atoms, the valency of elements began to be associated with the number of unpaired electrons (valence), thanks to which the bond between atoms is carried out. Thus, valence is determined by the number of unpaired electrons in an atom that take part in the formation of a chemical bond (in the ground or excited state). In general, valence is equal to the number of electron pairs connecting a given atom with atoms of other elements.
Most substances are characterized by the ability, depending on conditions, to be in one of three states of aggregation: solid, liquid or gaseous.
For example, water at normal pressure in the temperature range 0-100 o C is a liquid; at temperatures above 100 o C it can exist only in gaseous state, and at temperatures below 0 o C it is a solid substance.
Substances in the solid state are divided into amorphous and crystalline.
A characteristic feature of amorphous substances is the absence of a clear melting point: their fluidity gradually increases with increasing temperature. Amorphous substances include compounds such as wax, paraffin, most plastics, glass, etc.
Still, crystalline substances have a specific melting point, i.e. a substance with a crystalline structure passes from a solid to a liquid state not gradually, but abruptly, upon reaching a specific temperature. An example of crystalline substances is table salt, sugar, ice.
The difference is physical properties amorphous and crystalline solids is determined primarily by the structural features of such substances. What is the difference between a substance in amorphous and crystalline state, is easiest to understand from the following illustration:
As you can see, in an amorphous substance, unlike a crystalline one, there is no order in the arrangement of particles. If in a crystalline substance you mentally connect two atoms close to each other with a straight line, you can find that the same particles will lie on this line at strictly defined intervals:
Thus, in the case of crystalline substances, we can talk about such a concept as a crystal lattice.
Crystal lattice called a spatial framework connecting the points in space in which the particles that form the crystal are located.
The points in space at which the particles forming the crystal are located are called crystal lattice nodes .
Depending on which particles are located at the nodes of the crystal lattice, they are distinguished: molecular, atomic, ionic And metal crystal lattices .
In nodes molecular crystal lattice
Ice crystal lattice as an example of a molecular latticeThere are molecules within which the atoms are connected by strong covalent bonds, but the molecules themselves are held near each other by weak intermolecular forces. Due to such weak intermolecular interactions crystals with a molecular lattice are fragile. Such substances differ from substances with other types of structure by significantly lower melting and boiling points, do not conduct electric current, and may or may not dissolve in various solvents. Solutions of such compounds may or may not conduct electric current, depending on the class of the compound. Compounds with a molecular crystal lattice include many simple substances - nonmetals (hardened with H 2, O 2, Cl 2, rhombic sulfur S 8, white phosphorus P 4), as well as many complex substances - hydrogen compounds nonmetals, acids, nonmetal oxides, most organic matter. It should be noted that if a substance is in a gaseous or liquid state, it is inappropriate to talk about a molecular crystal lattice: it is more correct to use the term - molecular type buildings.
Diamond crystal lattice as an example of an atomic latticeIn nodes atomic crystal lattice
there are atoms. Moreover, all the nodes of such a crystal lattice are “linked” together through strong covalent bonds into a single crystal. In fact, such a crystal is one giant molecule. Due to their structural features, all substances with an atomic crystal lattice are solid, have high melting points, are chemically inactive, insoluble in either water or organic solvents, and their melts do not conduct electric current. It should be remembered that substances with atomic type structures from simple substances include boron B, carbon C (diamond and graphite), silicon Si, from complex substances - silicon dioxide SiO 2 (quartz), silicon carbide SiC, boron nitride BN.
For substances with ionic crystal lattice
lattice sites contain ions connected to each other through ionic bonds.
Because ionic bonds are quite strong, substances with an ionic lattice have relatively high hardness and refractoriness. Most often, they are soluble in water, and their solutions, like melts, conduct electric current.
Substances with an ionic crystal lattice include metal and ammonium salts (NH 4 +), bases, and metal oxides. A sure sign The ionic structure of a substance is the presence in its composition of both atoms of a typical metal and a non-metal.
Crystal lattice of sodium chloride as an example of an ionic lattice
observed in crystals of free metals, for example, sodium Na, iron Fe, magnesium Mg, etc. In the case of a metal crystal lattice, its nodes contain cations and metal atoms, between which electrons move. In this case, moving electrons periodically attach to cations, thus neutralizing their charge, and individual neutral metal atoms in return “release” some of their electrons, turning, in turn, into cations. In fact, “free” electrons do not belong to individual atoms, but to the entire crystal.
Such structural features lead to the fact that metals conduct heat and electric current well and often have high ductility (malleability).
The spread of melting temperatures of metals is very large. For example, the melting point of mercury is approximately minus 39 ° C (liquid under normal conditions), and tungsten is 3422 ° C. It should be noted that under normal conditions all metals except mercury are solids.
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, interconnected by electrostatic interaction.
Ionic crystal lattices have salts, alkalis, oxides active metals . 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. That's why ionic substances hard, refractory, non-volatile. Such substances are good dissolve in water.
Crystal lattice of sodium chloride
Sodium chloride crystal
Metal are called lattices that consist of positive ions and metal atoms and free electrons.
They are formed by substances with metal bond. At the nodes of the metal lattice there are atoms and ions (either atoms or ions, into which atoms easily turn, giving up their outer electrons for general 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.
This type of lattice has a diamond - one of allotropic modifications 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. So, 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 inside the molecules the atoms are connected by very strong covalent bonds, between the molecules themselves there are weak forces intermolecular attraction. Therefore, molecular crystals have low strength and hardness, low temperatures melting and boiling. Many molecular substances at room temperature they are liquids and gases. Such substances are volatile. For example, crystalline iodine and solid carbon monoxide (\(IV\)) (“dry ice”) evaporate without turning into liquid state. Some molecular substances have smell .
Simple substances in a solid state of aggregation have this type of lattice: noble gases With monoatomic 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).
Most solids have crystal structure , in which the particles from which it is “built” are in in a certain order, thereby creating crystal lattice. It is built from repeating identical structural units - unit cells, which communicates with neighboring cells, forming additional nodes. As a result, there are 14 different crystal lattices.
Types of crystal lattices.
Depending on the particles that stand at the lattice nodes, they are distinguished:
- metal crystal lattice;
- ionic crystal lattice;
- molecular crystal lattice;
- macromolecular (atomic) crystal lattice.
Metallic bond in crystal lattices.
Ionic crystals have increased fragility, because a shift in the crystal lattice (even a slight one) leads to the fact that like-charged ions begin to repel each other, and bonds break, cracks and splits form.
Molecular bonding of crystal lattices.
The main feature of the intermolecular bond is its “weakness” (van der Waals, hydrogen).
This is the structure of ice. Each water molecule is connected by hydrogen bonds to 4 molecules surrounding it, resulting in a tetrahedral structure.
Hydrogen bonding explains the high boiling point, melting point and low density;
Macromolecular connection of crystal lattices.
There are atoms at the nodes of a crystal lattice. These crystals are divided into 3 types:
- frame;
- chain;
- layered structures.
Frame structure diamond is one of the hardest substances in nature. The carbon atom forms 4 identical covalent bonds, which indicates the shape regular tetrahedron (sp 3 - hybridization). Each atom has a lone pair of electrons, which can also bond with neighboring atoms. As a result, a three-dimensional lattice is formed, in the nodes of which there are only carbon atoms.
It takes a lot of energy to destroy such a structure; the melting point of such compounds is high (for diamond it is 3500°C).
Layered structures speak of the presence of covalent bonds within each layer and weak van der Waals bonds between the layers.
Let's look at an example: graphite. Each carbon atom is in sp 2 - hybridization. The 4th unpaired electron forms a van der Waals bond between the layers. Therefore, the 4th layer is very mobile:
The bonds are weak, so they are easy to break, which can be observed in a pencil - “writing property” - the 4th layer remains on the paper.
Graphite is an excellent conductor electric current(electrons are able to move along the plane of the layer).
Chain structures have oxides (for example, SO 3 ), which crystallizes in the form of shiny needles, polymers, some amorphous substances, silicates (asbestos).
