What is a crystal lattice. Atomic, molecular, ionic and metallic crystal lattice
Chemistry is an amazing science. So much incredible can be found in seemingly ordinary things.
Everything material that surrounds us everywhere exists in several states of aggregation: gases, liquids and solids. Scientists have also isolated the 4th - plasma. At a certain temperature, a substance can change from one state to another. For example, water: when heated above 100, from a liquid form, it turns into steam. At temperatures below 0, it passes into the next aggregate structure - ice.
Whole material world has in its composition a mass of identical particles that are interconnected. These smallest elements are strictly arranged in space and form the so-called spatial framework.
Definition
A crystal lattice is a special structure of a solid substance, in which the particles are in a geometrically strict order in space. It is possible to detect nodes in it - places where elements are located: atoms, ions and molecules and internodal space.
Solids, depending on the range of high and low temperatures, are crystalline or amorphous - they are characterized by the absence of a specific melting point. When exposed to elevated temperatures, they soften and gradually turn into a liquid form. Such substances include: resin, plasticine.
In this regard, it can be divided into several types:
- atomic;
- ionic;
- molecular;
- metal.
But at different temperatures, one substance can have various forms and exhibit a variety of properties. This phenomenon is called allotropic modification.
Atomic type
In this type, atoms of one or another substance are located at the nodes, which are connected by covalent bonds. This type of bond is formed by a pair of electrons of two neighboring atoms. Due to this, they are connected evenly and in a strict order.
Substances with an atomic crystal lattice are characterized by the following properties: strength and high melting point. This type of bond is present in diamond, silicon and boron..
Ionic type
Oppositely charged ions are located at the nodes that create an electromagnetic field that characterizes the physical properties of a substance. These will include: electrical conductivity, refractoriness, density and hardness. Table salt and potassium nitrate are characterized by the presence of an ionic crystal lattice.
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Molecular type
In sites of this type, there are ions bound together by van der Waals forces. Due to weak intermolecular bonds, such substances, for example, ice, carbon dioxide and paraffin, are characterized by plasticity, electrical and thermal conductivity.
metal type
In its structure, it resembles a molecular one, but it still has stronger bonds. The difference of this type is that positively charged cations are located at its nodes. The electrons that are in the interstitial space, participate in the formation of an electric field. They are also called electric gas.
Simple metals and alloys are characterized by a metallic lattice type. They are characterized by the presence of metallic luster, plasticity, thermal and electrical conductivity. They can melt at different temperatures.
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Lesson type: Combined.
The main goal of the lesson: To give students concrete ideas about amorphous and crystalline substances, types of crystal lattices, to establish the relationship between the structure and properties of substances.
Lesson objectives.
Educational: to form concepts of the crystalline and amorphous state of solids, to acquaint students with various types of crystal lattices, to establish the dependence of the physical properties of a crystal on the nature of the chemical bond in the crystal and the type of crystal lattice, to give students basic ideas about the influence of the nature of the chemical bond and types of crystal lattices on properties of matter, to give students an idea of the law of constancy of composition.
Educational: to continue the formation of the worldview of students, to consider the mutual influence of the components of the whole - the structural particles of substances, as a result of which new properties appear, to cultivate the ability to organize their educational work, to follow the rules of working in a team.
Developing: to develop the cognitive interest of schoolchildren using problem situations; to improve the ability of students to establish a causal dependence of the physical properties of substances on the chemical bond and the type of crystal lattice, to predict the type of crystal lattice based on the physical properties of the substance.
Equipment: Periodic system of D.I. Mendeleev, collection “Metals”, non-metals: sulfur, graphite, red phosphorus, oxygen; Presentation “Crystal lattices”, models of crystal lattices of different types (salt, diamond and graphite, carbon dioxide and iodine, metals), samples of plastics and products from them, glass, plasticine, resins, wax, chewing gum, chocolate, computer, multimedia installation, video experiment “Sublimation of benzoic acid”.
During the classes
1. Organizational moment.
The teacher greets the students, fixes the absent ones.
Then he tells the topic of the lesson and the purpose of the lesson. Students write the topic of the lesson in a notebook. (Slide 1, 2).
2. Checking homework
(2 students at the blackboard: Determine the type of chemical bond for substances with the formulas:
1) NaCl, CO 2, I 2; 2) Na, NaOH, H 2 S (write down the answer on the board and are included in the survey).
3. Analysis of the situation.
Teacher: What does chemistry study? Answer: Chemistry is the science of substances, their properties and transformations of substances.
Teacher: What is a substance? Answer: Matter is what the physical body consists of. (Slide 3).
Teacher: What aggregate states of substances do you know?
Answer: There are three states of aggregation: solid, liquid and gaseous. (Slide 4).
Teacher: Give examples of substances that at different temperatures can exist in all three states of aggregation.
Answer: Water. Under normal conditions, water is in a liquid state, when the temperature drops below 0 0 C, the water turns into a solid state - ice, and when the temperature rises to 100 0 C, we get water vapor (gaseous state).
Teacher (addition): Any substance can be obtained in solid, liquid and gaseous form. In addition to water, these are metals that, under normal conditions, are in a solid state, when heated, they begin to soften, and at a certain temperature (t pl) they turn into a liquid state - they melt. Upon further heating, to the boiling point, the metals begin to evaporate, i.e. go into a gaseous state. Any gas can be converted into a liquid and solid state by lowering the temperature: for example, oxygen, which at a temperature (-194 0 C) turns into a blue liquid, and at a temperature (-218.8 0 C) solidifies into a snow-like mass consisting of crystals of blue color. Today in the lesson we will consider the solid state of matter.
Teacher: Name what solids are on your tables.
Answer: Metals, plasticine, table salt: NaCl, graphite.
Teacher: What do you think? Which of these substances is in excess?
Answer: Plasticine.
Teacher: Why?
Assumptions are made. If the students find it difficult, then with the help of the teacher they come to the conclusion that plasticine, unlike metals and sodium chloride, does not have a specific melting point - it (plasticine) gradually softens and becomes fluid. Such, for example, is chocolate that melts in the mouth, or chewing gum, as well as glass, plastics, resins, wax (when explaining, the teacher shows the class samples of these substances). Such substances are called amorphous. (slide 5), and metals and sodium chloride are crystalline. (Slide 6).
Thus, there are two types of solids : amorphous and crystalline. (slide 7).
1) Amorphous substances do not have a specific melting point and the arrangement of particles in them is not strictly ordered.
Crystalline substances have a strictly defined melting point and, most importantly, are characterized by the correct arrangement of the particles from which they are built: atoms, molecules and ions. These particles are located at strictly defined points in space, and if these nodes are connected by straight lines, then a spatial frame is formed - crystal cell.
The teacher asks problematic issues
How to explain the existence of solids with such different properties?
2) Why do crystalline substances split in certain planes upon impact, while amorphous substances do not have this property?
Listen to students' answers and lead them to conclusion:
The properties of substances in the solid state depend on the type of crystal lattice (primarily on what particles are in its nodes), which, in turn, is due to the type of chemical bond in a given substance.
Checking homework:
1) NaCl - ionic bond,
CO 2 - covalent polar bond
I 2 - covalent non-polar bond
2) Na - metallic bond
NaOH - ionic bond between Na + and OH - (O and H covalent)
H 2 S - covalent polar
front poll.
- What bond is called ionic?
- What bond is called covalent?
- What is a polar covalent bond? nonpolar?
- What is called electronegativity?
Conclusion: There is a logical sequence, the relationship of phenomena in nature: The structure of the atom-> EO-> Types of chemical bonds-> Type of crystal lattice-> Properties of substances . (slide 10).
Teacher: Depending on the type of particles and the nature of the connection between them, they distinguish four types of crystal lattices: ionic, molecular, atomic and metallic. (Slide 11).
The results are drawn up in the following table, a sample table for the students on the desk. (see Appendix 1). (Slide 12).
Ionic crystal lattices
Teacher: What do you think? For substances with what type of chemical bond will this type of lattice be characteristic?
Answer: For substances with an ionic chemical bond, an ionic lattice will be characteristic.
Teacher: What particles will be at the lattice nodes?
Answer: Jonah.
Teacher: What particles are called ions?
Answer: Ions are particles that have a positive or negative charge.
Teacher: What are the composition of ions?
Answer: Simple and complex.
The demo is a crystal lattice model of sodium chloride (NaCl).
Teacher's explanation: At the nodes of the crystal lattice of sodium chloride are sodium and chlorine ions.
There are no individual molecules of sodium chloride in NaCl crystals. The whole 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, non-volatile, brittle. Their melts conduct electric current (Why?), easily dissolve in water.
Ionic compounds are binary compounds of metals (I A and II A), salts, alkalis.
Atomic crystal lattices
Demonstration of crystal lattices of diamond and graphite.
The students have samples of graphite on the table.
Teacher: What particles will be in the nodes of the atomic crystal lattice?
Answer: Individual atoms are located at the nodes of the atomic crystal lattice.
Teacher: What kind of chemical bond between atoms will occur?
Answer: Covalent chemical bond.
Teacher's explanation.
Indeed, in the nodes of atomic crystal lattices there are individual atoms linked by covalent bonds. Since atoms, like ions, can be arranged differently in space, crystals of different shapes are formed.
Atomic crystal lattice of diamond
There are no molecules in these lattices. The whole crystal should be considered as a giant molecule. An example of substances with this type of crystal lattices are allotropic modifications of carbon: diamond, graphite; as well as boron, silicon, red phosphorus, germanium. Question: What are these substances in composition? Answer: Simple in composition.
Atomic crystal lattices are not only simple, but also complex. For example, aluminum oxide, silicon oxide. All these substances have very high melting points (diamond has over 3500 0 C), are strong and hard, non-volatile, practically insoluble in liquids.
Metallic crystal lattices
Teacher: Guys, you have a collection of metals on your tables, let's look at these samples.
Question: What is the chemical bond characteristic of metals?
Answer: metal. Communication in metals between positive ions by means of socialized electrons.
Question: What are the general physical properties of metals?
Answer: Luster, electrical conductivity, thermal conductivity, ductility.
Question: Explain why so many different substances have the same physical properties?
Answer: Metals have a single structure.
Demonstration of models of crystal lattices of metals.
Teacher's explanation.
Substances with a metallic bond have metallic crystal lattices
At the nodes of such lattices there are atoms and positive metal ions, and valence electrons move freely in the bulk of the crystal. The electrons electrostatically attract positive metal ions. This explains the lattice stability.
Molecular crystal lattices
The teacher demonstrates and names substances: iodine, sulfur.
Question: What do these substances have in common?
Answer: These substances are non-metals. Simple in composition.
Question: What is the chemical bond inside molecules?
Answer: The chemical bond inside the molecules is covalent non-polar.
Question: What are their physical properties?
Answer: Volatile, fusible, slightly soluble in water.
Teacher: Let's compare the properties of metals and non-metals. Students answer that the properties are fundamentally different.
Question: Why are the properties of nonmetals so different from those of metals?
Answer: Metals have a metallic bond, while non-metals have a non-polar covalent bond.
Teacher: Therefore, the type of lattice is different. Molecular.
Question: What particles are at the lattice sites?
Answer: Molecules.
Demonstration of the crystal lattices of carbon dioxide and iodine.
Teacher's explanation.
Molecular crystal lattice
As you can see, the molecular crystal lattice can have not only solid simple substances: noble gases, H 2, O 2, N 2, I 2, O 3, white phosphorus P 4, but also complex: solid water, solid hydrogen chloride and hydrogen sulfide. Most solid organic compounds have molecular crystal lattices (naphthalene, glucose, sugar).
The lattice sites contain non-polar or polar molecules. Despite the fact that the atoms inside the molecules are bound by strong covalent bonds, weak forces of intermolecular interaction act between the molecules themselves.
Conclusion: Substances are fragile, have low hardness, low melting point, volatile, capable of sublimation.
Question : What process is called sublimation or sublimation?
Answer : The transition of a substance from a solid state of aggregation immediately into a gaseous state, bypassing the liquid state, is called sublimation or sublimation.
Demonstration of experience: sublimation of benzoic acid (video experience).
Work with the completed table.
Annex 1. (Slide 17)
Crystal lattices, type of bond and properties of substances
| Lattice type | Types of particles at lattice sites |
Type of connection between particles | Substance examples | Physical properties substances |
| Ionic | ions | Ionic - strong bond | Salts, halides (IA,IIA), oxides and hydroxides of typical metals | Solid, strong, non-volatile, brittle, refractory, many soluble in water, melts conduct electricity |
| Atomic | atoms | 1. Covalent non-polar - the bond is very strong 2. Covalent polar - the bond is very strong |
Simple Substances A: diamond(C), graphite(C), boron(B), silicon(Si).
Compound substances: aluminum oxide (Al 2 O 3), silicon oxide (IY)-SiO 2 |
Very hard, very refractory, strong, non-volatile, insoluble in water |
| Molecular | molecules | Between molecules there are weak forces of intermolecular attraction, but inside the molecules there is a strong covalent bond | Solids under special conditions which, under ordinary conditions, are gases or liquids (O 2, H 2, Cl 2, N 2, Br 2, H 2 O, CO 2 ,HCl); sulfur, white phosphorus, iodine; organic matter |
Fragile, volatile, fusible, capable of sublimation, have a small hardness |
| metal | atom ions | Metal of different strength | Metals and alloys | Malleable, have gloss, ductility, heat and electrical conduction |
Question: What type of crystal lattice from the ones discussed above is not found in simple substances?
Answer: Ionic crystal lattices.
Question: What crystal lattices are typical for simple substances?
Answer: For simple substances - metals - a metal crystal lattice; for non-metals - atomic or molecular.
Work with the Periodic system of D.I. Mendeleev.
Question: Where are the metal elements in the Periodic Table and why? Elements are non-metals and why?
Answer: If you draw a diagonal from boron to astatine, then in the lower left corner from this diagonal there will be metal elements, because. at the last energy level, they contain from one to three electrons. These are elements I A, II A, III A (except for boron), as well as tin and lead, antimony and all elements of secondary subgroups.
Non-metal elements are located in the upper right corner of this diagonal, because at the last energy level contain from four to eight electrons. These are the elements IY A, Y A, YI A, YII A, YIII A and boron.
Teacher: Let's find non-metal elements that have simple substances have an atomic crystal lattice (Answer: C, B, Si) and molecular ( Answer: N, S, O , halogens and noble gases ).
Teacher: Formulate a conclusion on how you can determine the type of crystal lattice of a simple substance, depending on the position of the elements in the Periodic system of D.I. Mendeleev.
Answer: For metal elements that are in I A, II A, IIIA (except for boron), as well as tin and lead, and all elements of secondary subgroups in a simple substance, the lattice type is metallic.
For non-metal elements IY A and boron in a simple substance, the crystal lattice is atomic; and the elements Y A, YI A, YII A, YIII A in simple substances have a molecular crystal lattice.
We continue to work with the completed table.
Teacher: Look carefully at the table. What pattern is observed?
We carefully listen to the answers of the students, after which, together with the class, we conclude:
There is the following pattern: if the structure of substances is known, then their properties can be predicted, or vice versa: if the properties of substances are known, then the structure can be determined. (Slide 18).
Teacher: Look carefully at the table. What other classification of substances can you suggest?
If the students find it difficult, the teacher explains that Substances can be divided into molecular and non-molecular substances. (Slide 19).
Molecular substances are made up of molecules.
Substances of non-molecular structure consist of atoms, ions.
Law of constancy of composition
Teacher: Today we will get acquainted with one of the basic laws of chemistry. This is the law of composition constancy, which was discovered by the French chemist J. L. Proust. The law is valid only for substances of molecular structure. At present, the law reads as follows: “Molecular chemical compounds, regardless of the method of their preparation, have a constant composition and properties.” But for substances with a nonmolecular structure, this law is not always true.
Theoretical and practical value law is that on its basis the composition of substances can be expressed using chemical formulas (for many substances of non-molecular structure chemical formula shows the composition of not a real, but a conditional molecule).
Conclusion: The chemical formula of a substance contains a lot of information.(Slide 21)
For example SO 3:
1. A specific substance is sulfuric gas, or sulfur oxide (YI).
2. Type of substance - complex; class - oxide.
3. Qualitative composition - consists of two elements: sulfur and oxygen.
4. Quantitative composition - the molecule consists of 1 sulfur atom and 3 oxygen atoms.
5. Relative molecular weight - M r (SO 3) \u003d 32 + 3 * 16 \u003d 80.
6. Molar mass - M (SO 3) \u003d 80 g / mol.
7. Lots of other information.
Consolidation and application of acquired knowledge
(Slide 22, 23).
Tic-tac-toe game: cross out vertically, horizontally, diagonally substances that have the same crystal lattice.
Reflection.
The teacher asks the question: “Guys, what new did you learn in the lesson?”.
Summing up the lesson
Teacher: Guys, let's sum up the main results of our lesson - answer the questions.
1. What classifications of substances did you learn?
2. How do you understand the term crystal lattice.
3. What types of crystal lattices do you now know?
4. What pattern of structure and properties of substances did you learn about?
5. In what state of aggregation do substances have crystal lattices?
6. What basic law of chemistry did you learn in class?
Homework: §22, abstract.
1. Make formulas of substances: calcium chloride, silicon oxide (IY), nitrogen, hydrogen sulfide.
Determine the type of crystal lattice and try to predict: what should be the melting points of these substances.
2. Creative task -> compose questions for the paragraph.
The teacher thanks for the lesson. Gives grades to students.
Solids exist in a crystalline and amorphous state and predominantly have a crystalline structure. It is distinguished by the correct location of particles at precisely defined points, is characterized by periodic repetition in volume. If we mentally connect these points with straight lines, we get a spatial frame, which is called the crystal lattice. The term "crystal lattice" refers to a geometric image that describes a three-dimensional periodicity in the arrangement of molecules (atoms, ions) in a crystal space.
The points where particles are located are called lattice nodes. Internodal connections operate inside the frame. The type of particles and the nature of the connection between them: molecules, atoms, ions - determine In total, four such types are distinguished: ionic, atomic, molecular and metallic.
If ions are located at the lattice sites (particles with a negative or positive charge), then this is an ionic crystal lattice characterized by bonds of the same name.
These bonds are very strong and stable. Therefore, substances with this type of structure have a sufficiently high hardness and density, non-volatile and refractory. At low temperatures they behave as dielectrics. However, during the melting of such compounds, the geometrically correct ionic crystal lattice (the arrangement of ions) is violated and strength bonds decrease.
At a temperature close to the melting point, crystals with an ionic bond are already capable of conducting an electric current. Such compounds are readily soluble in water and other liquids that are composed of polar molecules.
The ionic crystal lattice is characteristic of all substances with an ionic type of bond - salts, metal hydroxides, binary compounds of metals with non-metals. has no direction in space, because each ion is associated with several counterions at once, the strength of interaction of which depends on the distance between them (Coulomb's law). Ionically bound compounds have a non-molecular structure, they are solids with ionic lattices, high polarity, high melting and boiling points, which are electrically conductive in aqueous solutions. Compounds with ionic bonds in their pure form are almost never found.
The ionic crystal lattice is inherent in some hydroxides and oxides of typical metals, salts, i.e. substances with ionic
In addition to ionic bonds in crystals, there are metallic, molecular and covalent bonds.
Crystals that have a covalent bond are semiconductors or dielectrics. Typical examples of atomic crystals are diamond, silicon and germanium.
Diamond is a mineral, an allotropic cubic modification (form) of carbon. Crystal cell diamond - atomic, very complex. At the nodes of such a lattice are atoms interconnected by extremely strong covalent bonds. A diamond is made up of individual carbon atoms, one at a time in the center of a tetrahedron whose vertices are the four closest atoms. Such a lattice is characterized by a face-centered cubic, which determines the maximum hardness of diamond and a rather high melting point. There are no molecules in the diamond lattice - and the crystal can be viewed as one imposing molecule.
In addition, it is characteristic of silicon, solid boron, germanium and compounds of individual elements with silicon and carbon (silica, quartz, mica, river sand, carborundum). In general, there are relatively few representatives with an atomic lattice.
What exists in nature is formed by a large number of identical particles that are interconnected. All substances exist in three aggregate states: gaseous, liquid and solid. When thermal motion is difficult (at low temperatures), as well as in solids, the particles are strictly oriented in space, which is manifested in their precise structural organization.
The crystal lattice of a substance is a structure with a geometrically ordered arrangement of particles (atoms, molecules or ions) at certain points in space. In various lattices, the internodal space and the nodes themselves are distinguished - the points at which the particles themselves are located.
There are four types of crystal lattice: metallic, molecular, atomic, ionic. The types of lattices are determined in accordance with the type of particles located at their nodes, as well as the nature of the bonds between them.
A crystal lattice is called a molecular lattice if molecules are located at its nodes. They are interconnected by relatively weak intermolecular forces, called van der Waals forces, but the atoms themselves inside the molecule are connected by a much stronger or non-polar one). The molecular crystal lattice is characteristic of chlorine, solid hydrogen, and other substances that are gaseous at ordinary temperatures.
The crystals that form the noble gases also have molecular lattices made up of monatomic molecules. Most solid organic matter have exactly the same structure. The number of which is characterized by a molecular structure is very small. These are, for example, solid hydrogen halides, natural sulfur, ice, solid simple substances, and some others.
When heated, relatively weak intermolecular bonds are destroyed quite easily, therefore, substances with such lattices have very low melting points and low hardness, they are insoluble or slightly soluble in water, their solutions practically do not conduct electric current, and are characterized by significant volatility. The minimum boiling and melting points are for substances from non-polar molecules.
Such a crystal lattice is called metallic, the nodes of which are formed by atoms and positive ions (cations) of the metal with free valence electrons (hooked off from the atoms during the formation of ions), randomly moving in the volume of the crystal. However, these electrons are essentially semi-free, since they can move freely only within the limits that this crystal lattice limits.
Electrostatic electrons and positive metal ions are mutually attracted, which explains the stability of the metal crystal lattice. A set of free moving electrons is called an electron gas - it provides good electricity and When an electric voltage appears, the electrons rush to the positive particle, participating in the creation of an electric current and interacting with ions.
The metallic crystal lattice is characteristic mainly for elemental metals, as well as for compounds of various metals with each other. The main properties that are inherent in metal crystals (mechanical strength, volatility, fluctuate quite strongly. However, such physical properties as ductility, ductility, high electrical and thermal conductivity, characteristic metallic luster are characteristic only of crystals with a metal lattice.
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 very name means in Greek "indestructible." Diamonds have long been regarded as miraculous stones. It was believed that a person wearing diamonds does not know stomach diseases, poison does not affect him, he retains his memory and cheerful mood until old age, enjoys royal favor.
☼ A diamond subjected to jewelry processing - cutting, polishing, is called a diamond.
During melting, as a result of thermal vibrations, the order of the particles is violated, they become mobile, while the nature of the chemical bond is not violated. Thus, there are no fundamental differences between the solid and liquid states.
Fluidity appears in the liquid (i.e., the ability to take the shape of a vessel).
liquid crystalsLiquid crystals were discovered at the end of the 19th century, but have been studied in the last 20-25 years. Many display devices modern technology, for example, some electronic clocks, mini-computers, run on liquid crystals.
In general, the words "liquid crystals" sound no less unusual than "hot ice". However, in fact, ice can also be hot, because. at pressures over 10,000 atm. water ice melts at temperatures above 200 0 C. The unusual combination of "liquid crystals" is that the liquid state indicates the mobility of the structure, and the crystal assumes strict order.
If a substance consists of polyatomic molecules of an elongated or lamellar shape and having an asymmetric 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 freely move parallel to themselves, i.e. the system acquires the fluidity characteristic of a liquid. At the same time, the system retains an ordered structure that determines the properties characteristic of crystals.
The high mobility of such a structure makes it possible to control it by very weak influences (thermal, electrical, etc.), i.e. purposefully change the properties of a substance, including optical ones, with very little energy, which is used in modern technology.
Types of crystal latticesAny chemical substance is formed by a large number of identical particles that are interconnected.
At low temperatures, when thermal motion is hindered, the particles are strictly oriented in space and form crystal lattice.
Crystal cell - This 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 the conditions (p, t,…) exists in various crystalline forms (that is, 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 found in meteorites and obtained artificially, and its structure is still being studied.
☼ Soot, coke, charcoal attributed to 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 they called "mirror carbon". Mirror carbon is chemically inert, heat-resistant, impervious to gases and liquids, has a smooth surface and absolute compatibility with living tissues.
☼ The name graphite comes from the Italian "graffito" - I write, I draw. Graphite is a dark-gray crystals with a slight metallic sheen, has a layered lattice. Separate layers of atoms in a graphite crystal, relatively weakly bonded to each other, are easily separated from each other.
TYPES OF CRYSTAL LATTICES
|
ionic |
metallic |
|||
|
What is in the nodes of the crystal lattice, structural unit |
ions |
atoms |
molecules |
atoms and cations |
|
Type of chemical bond between knot particles |
ionic |
covalent: polar and non-polar |
metallic |
|
|
Forces of interaction between crystal particles |
electrostatic cal |
covalent |
intermolecular nye |
electrostatic cal |
|
Physical properties due to the crystal lattice |
the attractive forces between the ions are strong, T pl. (refractory), Easily soluble in water melt and solution conducts electric current, non-volatile (no smell) |
covalent bonds between atoms are large, T pl. and T kip very, are not soluble in water the melt does not conduct electricity |
The attractive forces between molecules are small T pl. ↓, Some dissolve in water They have an odor - they are volatile |
interaction forces are great T pl. , High thermal and electrical conductivity |
|
Aggregate state of matter under normal conditions |
solid |
solid |
hard, gaseous, liquid |
hard, liquid(N g) |
|
Examples |
most salts, alkalis, typical metal oxides |
C (diamond, graphite), Si, Ge, B, SiO 2, CaC 2, SiC (carborundum), BN, Fe 3 C, TaC (t pl. \u003d 3800 0 С) Red and black phosphorus. Oxides of some metals. |
all gases, liquids, most non-metals: inert gases, halogens, H 2 , N 2 , O 2 , O 3 , P 4 (white), S 8 . Hydrogen compounds of non-metals, oxides of non-metals: H 2 O, CO 2 "dry ice". most organic compounds. |
Metals, alloys |
If the crystal growth rate is low upon cooling, a glassy state (amorphous) is formed.
- The relationship between the position of an element in the Periodic system 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 elementary substance.
|
group |
|||||||||
|
III |
VII |
VIII |
|||||||
|
P e R And O d |
H2 |
||||||||
|
N 2 |
O2 |
F2 |
|||||||
|
III |
P4 |
S8 |
Cl2 |
||||||
|
Br2 |
|||||||||
|
I 2 |
|||||||||
|
Type crystal lattice |
metallic |
nuclear |
molecular |
||||||
The simple substances of the remaining elements have a metallic crystal lattice.
FIXING
Study the lecture material, 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 → Forces of interaction between particles of the crystal → Physical properties due to the crystal lattice → Aggregate state of matter under normal conditions → Examples
Complete the tasks on this topic:
- What type of crystal lattice do the following substances widely used in everyday life have: water, acetic acid (CH 3 COOH), sugar (C 12 H 22 O 11), potash fertilizer (KCl), river sand (SiO 2) - melting point 1710 0 C , ammonia (NH 3), table salt? Make a generalized conclusion: what properties of a substance can determine the type of its crystal lattice?
- According to the formulas of the given substances: SiC, CS 2, NaBr, C 2 H 2 - 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 number 1. "Crystal Grids"
- Trainer number 2. "Test tasks"
- Test (self-control):
1) Substances having a molecular crystal lattice, as a rule:
a). refractory and highly soluble in waterb). fusible and volatile
V). Solid and electrically conductive
G). Thermally conductive and plastic
2) The concept of "molecule" not applicable in relation to the structural unit of the substance:
a). water
b). oxygen
V). diamond
G). ozone
3) The atomic crystal lattice is characteristic for:
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:
A). molecular
b). nuclear
V). ionic
G). metallic
