Alkanes - nomenclature, preparation, chemical properties. Alkanes Alkanes summary briefly

The use of alkanes is quite diverse - they are used as fuel, as well as in mechanics, medicine, etc. The role of these chemical compounds in the life of modern man can hardly be overestimated.

Alkanes: properties and brief description

Alkanes are non-cyclic carbon compounds in which the carbon atoms are linked by simple saturated bonds. These substances represent a whole range with certain properties and characteristics. as follows:

N here represents the number of carbon atoms. For example, CH3, C2H6.

The first four representatives of the alkanes series are gaseous substances: methane, ethane, propane and butane. The following compounds (C5 to C17) are liquids. The series continues with compounds that are solids under normal conditions.

As for chemical properties, alkanes are low-active - they practically do not interact with alkalis and acids. By the way, it is the chemical properties that determine the use of alkanes.

However, these compounds are characterized by certain reactions, including the replacement of hydrogen atoms, as well as molecular splitting processes.

• The most characteristic reaction is halogenation, in which hydrogen atoms are replaced by halogens. Great importance have chlorination and bromination reactions of these compounds.
• Nitration is the replacement of a hydrogen atom with a nitro group during a reaction with a dilute (10% concentration) Under normal conditions, alkanes do not react with acids. In order to carry out such a reaction, a temperature of 140 °C is needed.
• Oxidation - under normal conditions, alkanes are not affected by oxygen. However, after ignition in air, these substances enter into the final products of which are water and
• Cracking - this reaction occurs only in the presence of the necessary catalysts. The process involves the cleavage of stable homologous bonds between carbon atoms. For example, when butane is cracked, the reaction can produce ethane and ethylene.
• Isomerization - as a result of the action of certain catalysts, some rearrangement of the carbon skeleton of the alkane is possible.

Applications of alkanes

The main natural source of these substances are such valuable products as natural gas and oil. The areas of application of alkanes today are very wide and varied.

For example, gaseous substances used as a valuable source of fuel. An example is methane, which natural gas is made of, as well as a propane-butane mixture.

Another source of alkanes is oil , the importance of which for modern humanity is difficult to overestimate. Petroleum products include:

• gasoline - used as fuel;
• kerosene;
• diesel fuel, or light gas oil;
• heavy gas oil, which is used as a lubricating oil;
• the remains are used to make asphalt.

Petroleum products are also used to produce plastics, synthetic fibers, rubbers and some detergents.

Vaseline and petroleum jelly are products that consist of a mixture of alkanes. They are used in medicine and cosmetology (mainly for the preparation of ointments and creams), as well as in perfumery.

Paraffin is another well-known product, which is a mixture of solid alkanes. This is a solid white mass, the heating temperature of which is 50 - 70 degrees. In modern production, paraffin is used to make candles. Matches are impregnated with the same substance. In medicine, various thermal procedures are performed using paraffin.

Alkanes are obtained from petroleum products, natural gas, and coal. The main use of alkanes is as fuel. The substances are also used to make solvents, cosmetics, and asphalt.

Description

Alkanes are a class of saturated or saturated hydrocarbons. This means that alkane molecules contain the maximum number of hydrogen atoms. The general formula of compounds of the homologous series of alkanes is C n H 2n+2. The names of substances are composed of the Greek numerals and the suffix -an.

The physical and chemical properties of alkanes depend on their structure. As the number of carbon atoms in a molecule increases, a transition occurs from gaseous substances to solid compounds.

The physical state of alkanes depending on the number of carbon atoms:

• C 1 -C 4- gases;
• From 5 to 15- liquids;
• C 16 -C 390- solids.

Gases burn with a blue flame, releasing a large amount of heat. Alkanes containing 18-35 carbon atoms are waxy, soft substances. Paraffin candles are made from their mixture.

Rice. 1. Paraffin candles.

With increasing molecular weight in the homologous series, the melting and boiling points increase.

Application

Alkanes are isolated from minerals - oil, gas, coal. At different stages of processing, gasoline, kerosene, and fuel oil are obtained. Alkanes are used in medicine, cosmetology, and construction.

Rice. 2. Oil contains liquid alkanes.

The table describes the main areas of application of saturated hydrocarbons.

Rice. 3. Tar.

Alkanes are used in the manufacture of rubber, synthetic fabrics, plastics, and surfactants. Propane and butane in liquefied form are used to refill cylinders for extinguishing fires.

What have we learned?

We learned briefly about the scope of application of alkanes. Saturated hydrocarbons in gaseous, liquid, and solid states are used in the chemical, food, paper, energy industries, cosmetology and construction. Alkanes are used to produce solvents, paints, varnishes, soaps, candles, ointments, and asphalt. Gasoline, kerosene, and fuel oil, consisting of liquid alkanes, are used as fuel. Gaseous alkanes are used in everyday life and for the production of aerosols. The main sources of alkanes are oil, natural gas, and coal.

Test on the topic

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Chemistry lesson using ICT on the topic "Alkanes"

The purpose of the lesson: introduce students to alkanes and identify their important role in industry.

Lesson objectives:

Educational: consider the homologous series of saturated hydrocarbons, structure, physical and chemical properties, methods of their production during the processing of natural gas, the possibility of their production from natural sources: natural and associated petroleum gases, oil and coal.

Developmental: develop the concept of the spatial structure of alkanes; development of cognitive interests, creative and intellectual abilities, development of independence in acquiring new knowledge using new technologies.

Educational: show the unity of the material world using the example of the genetic connection of hydrocarbons of different homologous series obtained from the processing of natural and associated petroleum gases, oil and coal.

Equipment: computer, multimedia projector, screen, presentation.

During the classes

I. Organizational moment. (Inform the purpose and topic of the lesson).

II. Learned new material.

Lesson topic: "Alkanes". Slide No. 1

Plan for studying alkanes. Slide number 2

Definition. General formula of the class of hydrocarbons.

Homologous series.

Types of isomerism.

Structure of alkanes.

Physical properties.

Methods of obtaining.

Chemical properties.

Application.

Alkanes. (Saturated hydrocarbons. Paraffins. Saturated hydrocarbons.)

Alkanes are hydrocarbons in molecules in which all carbon atoms are connected by single bonds and have the general formula: C n H 2n+2 Slide No. 3

What are homologues?

Homologous series of methane

CH 4 methane

C 2 H 6 ethane

C 3 H 8 propane

C 4 H 10 butane

C 5 H 12 pentane

C 6 H 14 hexane

C 7 H 16 heptane

C 9 H 20 nonane

Homologues are substances that are similar in structure and properties and differ by one or more CH 2 groups.

Structural isomerism:

Algorithm.

1. Selecting the main circuit: Slide No. 5

2. Numbering of atoms of the main chain: Slide No. 6

3. Formation of the title: Slide No. 7

2 - methylbutane

Structure of alkanes.

The carbon atom in all organic substances is in an “excited” state and has four unpaired electrons at the outer level.

Each electron cloud has a reserve of energy: the s-cloud has a smaller reserve of energy than the p-cloud; in the carbon atom they are in different energy states. Therefore, when a chemical bond is formed, hybridization occurs, i.e., the alignment of electron clouds in terms of energy reserve. This is reflected in the shape and direction of the clouds; a restructuring (spatial) of the electron clouds occurs.

As a result of sp3 hybridization, all four valence electron clouds are hybridized: the bond angle between these axes of the hybridized clouds is 109° 28", therefore the molecules have a spatial tetrahedral shape, the shape of the carbon chains is zigzag; the carbon atoms are not on the same straight line, because during rotation atoms bond angles remain the same.

All organic substances are built mainly through covalent bonds. Carbon-carbon and carbon-hydrogen bonds are referred to as sigma bonds - a bond formed when atomic orbitals overlap along a line passing through the atomic nuclei. Rotation around sigma bonds is possible, since this bond has axial symmetry. Slide number 13

Physical properties.

CH 4:C 4 H 10 - gases

Boiling point: -161.6:-0.5 °C

Melting temperature: -182.5:-138.3 °C

C 5 H 12: C 15 H 32 - liquids

Boiling point: 36.1:270.5 °C

Melting temperature: -129.8:10 °C

Boiling point: 287.5 °C

Melting temperature: 20 °C

With an increase in the relative molecular weights of saturated hydrocarbons, their boiling and melting points naturally increase. Slide number 14

Receipt.

In industry

1) cracking of petroleum products:

C 16 H 34 - C 8 H 18 + C 8 H 16

2) In the laboratory:

a) Hydrolysis of carbides:

Al 4 C 3 +12 H 2 O = 3 CH 4 + 4 Al(OH) 3

b) Wurtz reaction:

C 2 H 5 Cl + 2Na - C 4 H 10 + 2NaCl

c) Decarboxylation of sodium salts of carbon salts:

CH 3 COONa + 2NaOH - CH 4 + Na 2 CO 3 Slide No. 15

Chemical properties

Alkanes are characterized by the following types of chemical reactions:

Substitution of hydrogen atoms;

Dehydrogenation;

Oxidation.

1) Substitution of hydrogen atoms:

A) Halogenation reaction:

CH 4 +Cl 2 - CH 3 Cl + HCl

B) Nitration reaction (Konovalov):

CH 4 + HNO 3 - CH 3 -NO 2 + H 2 O + Q

B) Sulfonation reaction:

CH 4 + H 2 SO 4 - CH 3 -SO 3 H + H 2 O + Q

2) Isomerization reaction:

CH 3 -CH 2 -CH 2 -CH 2 -CH 3 - CH 3 -CH-CH 2 -CH 3

3) Reaction with water vapor:

CH 4 + H 2 O = CO + 3H 2

4) Dehydrogenation reaction:

2CH 4 - HC=CH + 3H 2 + Q

5) Oxidation reaction:

CH 4 + O 2 - H 2 C=O + H 2 O

6) Methane combustion:

CH 4 + 2O 2 CO 2 + 2H 2 O + Q Slide number 20

Application.

(Perhaps pre-prepared student speeches.)

Widely used as fuel, including for

internal combustion engines, as well as in the production of soot

(1 - cartridges; 2 - rubber; 3 - printing ink), when obtaining organic substances (4 - solvents; 5 - refrigerants used in refrigeration units; 6 - methanol; 7 - acetylene) Slide No. 21

III. Consolidation.

List all possible isomers for heptane and name them.

Make the 2 closest homologs for pentane and name them.

Determine the saturated hydrocarbon whose vapor density in air is 2. (C 4 H 10).

Textbook: No. 12 (p. 33).

IV. Homework: Textbook O.S. Gabrielyan (grade 10 basic level): 3, ex. 4, 7, 8 (page 32).

Literature.

Gorkovenko M. Yu. Lesson developments in chemistry for educational sets of O. S. Gabrielyan and others, grade 10 (11). M.: "VEKO", 2008

Chemistry lessons in 10th grade according to a two-hour program by Gabrielyan O.S.

Abbakumov A.V.

(lecture)
Lesson objectives: consider the main natural sources of hydrocarbons in the light of two directions of their use: as energy raw materials and the basis of chemical synthesis. Using this material, repeat, consolidate and generalize previously acquired knowledge about the properties and application of saturated hydrocarbons.
Equipment: collections “Oil and petroleum products”, “Coal and products of its processing”, tables on the composition of natural and associated gases, portraits of M.V. Lomonosov, D.I. Mendeleeva, N.D. Zelinsky, V.G. Shukhova.
^ Progress of the lesson.
I. Preparation for the lesson(check the readiness of groups of students, equipment, class for the lesson; mark absent students in the log; report the topic and goals of the lesson).
II. Lecture.

Lecture plan.

1. 
   Natural gases and their use.
2. 
   The concept of hydrocarbons.
3. 
   Electronic and spatial structure of the methane molecule.
4. 
   Homologous series of saturated hydrocarbons.
5. 
   Isomerism and nomenclature of alkanes.
6. 
   Methods of obtaining and physical properties alkanes
7. 
   Chemical properties and applications of alkanes.

1. Natural gases and their uses.

Our country ranks first in the world in terms of natural gas reserves. About 200 natural gas fields have been discovered in Russia. The vast majority of produced gas is used as fuel.

Advantages of gas over other types of fuel:

• 
  high calorific value (up to 54,400 kJ is released when 1 m 3 of natural gas is burned);
• 
  cheapness;
• 
  environmental cleanliness;
• 
  easy transportation via gas pipelines.

Thus, natural gas today is one of the best types of fuel for domestic and industrial (cars, metallurgical, glass and soap furnaces, etc.) needs. In addition, natural gas serves as a valuable and cheap raw material for the chemical industry.
^ Composition of natural gas .

The composition of natural gas from different fields is different. However, the gases of all fields contain hydrocarbons with a small relative molecular weight.

Composition of natural gas:

• 
  80-90% methane;
• 
  2-3% of its homologues (ethane, propane, butane);
• 
  low content of impurities (hydrogen sulfide, nitrogen, noble gases, carbon dioxide and water vapor).

2. The concept of hydrocarbons.

The name of the group of organic compounds that we are beginning to study today reflects their composition.

Hydrocarbons are compounds consisting only of carbon and hydrogen atoms.
Classification of hydrocarbons

Hydrocarbons

Cyclic (carbocyclic) Acyclic

Cyclic (carbocyclic) are compounds that contain one or more rings consisting only of carbon atoms. They, in turn, are divided into aromatic and non-aromatic.

Acyclic hydrocarbons include organic compounds whose carbon skeleton molecules are open chains.

These chains can be formed by single bonds (alkanes), contain one double bond (alkenes), two double bonds (dienes), one triple bond (alkynes).
3. ^ Electronic and spatial structure of the methane molecule .

Today we begin to study the first class of hydrocarbons - alkanes (saturated, saturated, paraffinic hydrocarbons).

^ Alkanes are hydrocarbons in whose molecules the atoms are connected by single bonds and which correspond to the general formula C n H 2 n +2 .

[ Demonstration of the ratio of methane to potassium permanganate solution and bromine water].

The simplest representative of this class, methane, has been known to people for a very long time. It was called swamp, or mine, gas.

The carbon atom in methane is in a state of sp 3 hybridization. Carbon in this case has four equivalent hybrid orbitals, the axes of which are directed towards the vertices of the tetrahedron. The angle between the axes of these orbitals is 109°28". /Image of the structure of the carbon atom in sp 3 -hybrid state /.

The electronic structure of the carbon atom determines the spatial arrangement of atoms in the methane molecule. All four covalent C–H bonds are formed due to the overlap of the sp 3 orbitals of the carbon atom and the s orbital of the hydrogen. All bonds in the methane molecule are of the σ type. The centers of the nuclei of hydrogen atoms lie at the vertices of a regular tetrahedron. /Demonstration of a methane molecule model/ .

Almost free rotation is possible around a single carbon-carbon bond, and alkane molecules can take on a wide variety of shapes. /Demonstration on a model of a butane molecule/ .

Carbon–carbon bonds are nonpolar and poorly polarizable. The length of the C–C bond in alkanes is 0.154 nm. The C–H bond is weakly polar.

The absence of polar bonds in the molecules of saturated hydrocarbons leads to the fact that they are poorly soluble in water.
4. ^ Homologous series of saturated hydrocarbons .

Saturated hydrocarbons make up the homologous series of methane.

A homologous series is a set of organic compounds that have a similar structure and properties and differ from each other in composition by one or more groups - CH 2 – (homologous difference).

Representatives of the same homologous series are called homologs.

Using the first four representatives as an example, derive the general formula of alkanes:

Methane - CH 4; Ethane - C 2 H 6; Propane - C 3 H 8; Butane - C 4 H 10; Pentane - C 5 H 12.

(The general formula of alkanes is C n H 2 n +2).
5. ^ Isomerism and nomenclature of alkanes .

Alkanes are characterized by structural isomerism. Structural isomers differ from each other in the structure of the carbon skeleton.
Basics of IUPAC nomenclature.

1. 
   Selecting the main circuit.
2. 
   Numbering of main chain atoms.
3. 
   Formation of the name.

Depending on the number of radicals connected to a carbon atom, there are: primary, secondary, tertiary and quaternary carbon atoms.
6. Methods of preparation and physical properties of alkanes.

1. 
   Cracking of petroleum products
2. 
   Hydrogenation of alkenes
3. 
   Pyrolysis of carboxylic acid salts
4. 
   Wurtz reaction

1). Combustion reaction.

Numerous chemical reactions occur both around a person and in him. Sometimes we simply do not pay attention to these chemical phenomena. When we light gas in the kitchen or flick a lighter, ride in a car or watch on TV the tragic consequences of an explosion in a mine, we are witnesses to the combustion reaction of alkanes [Demonstration of methane combustion].

Like most organic substances, saturated hydrocarbons, when burned, form water vapor and carbon dioxide:

CH 4 + 2O 2 → CO 2 + 2H 2 O

When saturated hydrocarbons burn, a large amount of heat is released, which predetermines their use as fuel.
2). ^ Substitution reaction .

Remember the structure of methane. Carbon atoms have completely exhausted their valence capabilities. To get another substance from methane, you need to break the C–H bonds and replace the hydrogen with another atom or group of atoms. Thus, alkanes are characterized by substitution reactions.

׀ ׀

H−C−H + Cl−Cl → H−C−Cl + H−Cl

If there is a sufficient amount of halogen, the reaction continues until polysubstituted products are formed.

Only chlorine and bromine can be used as halogen in such reactions. The reaction with fluorine occurs explosively and leads to the destruction of the alkane molecule, while iodine, as a less active halogen, is not capable of such a transformation.
3). ^ Decomposition reaction .

When alkanes are heated without access to air, a wide variety of transformations used in industry occur. When methane is heated to 1000°C, methane pyrolysis begins - decomposition into simple substances.

CH 4
C + 2H 2

2CH 4
^CH≡CH + 3H 2

Thus, hydrocarbons with double and triple bonds can be obtained from paraffins.

4). Dehydrogenation reaction.

For methane homologues, another practically important process is possible: the dehydrogenation reaction. This transformation occurs in the presence of a catalyst at elevated temperatures and leads to the formation of ethylene hydrocarbons.

Н−С−С−Н
Н−С=С−Н + Н−Н

׀ ׀

It should be noted that at room temperature, saturated hydrocarbons are very inert compounds that do not interact with aggressive substances. The most typical reactions for alkanes are radical substitution reactions (halogenation, nitration).

Just as the structure of a substance determines its reactivity, its properties largely determine the areas of application of compounds.

Gaseous alkanes are not only household and industrial fuels, but also raw materials for the chemical industry. From them, halogen derivatives are obtained, including fully fluorinated hydrocarbons (freons), which are refrigerants for household and industrial refrigerators and air conditioners. Unsaturated hydrocarbons and then polymeric materials are obtained from ethane and propane. Liquid hydrocarbons are, first of all, fuel for engines of various types (a supersonic aircraft consumes up to 100 liters of kerosene per minute!), solvents, and raw materials for the production of alkenes.

III. Homework:§ 3 ex. 4

Lesson plan No.19

Date Subject Chemistry group

FULL NAME. teacher: Kayyrbekova I.A.

Subject : Alkanes. Homologous series, isomers, nomenclature, properties and preparation of alkanes Goals : Study alkanes, as one of the classes of acyclic compounds.

Tasks:

Educational:

Continue to develop the concept of the main classes of hydrocarbons; begin to form a concept about carbocyclic compounds; study the structure, nomenclature and isomerism of alkanes; consider the main methods of obtaining and using alkanes; study the chemical properties of alkanes and genetic relationships with other classes of hydrocarbons.

Educational:

Develop the cognitive sphere of students; general educational skills of students; develop the ability to analyze and draw independent conclusions;

Educational:

Instill a culture of knowledge work and collaboration; cultivate discipline; collectivism and sense of responsibility; contribute to the creation of a favorable psycho-emotional climate in the classroom;

Lesson type: lesson in learning new knowledge.

II. Expected results:

A) Students should know: structure, properties of alkanes

Ә) Students should be able to: compare, prove

b) students must master: working with chemical reagents while observing safety regulations

III. Method and techniques for each stage of the lesson: verbal-visual, explanatory-illustrative IV. Facilities: interactive whiteboard, textbook

During the classes

1.Organizational point: Check student attendance. Introduce the objectives of the lesson.

2. Preparation for the perception of new material: Theoretical dictation:

A) Basic provisions of the theory of chemical structure of A. M. Butlerov. Give examples.

B) what are called isomers?

C) The main mechanisms for breaking ties?

3. Explanations of new material (learning new knowledge).

Plan:

The concept of hydrocarbons. Saturated hydrocarbons.

The structure of the methane molecule.

Homologous series of methane.

Structure of saturated hydrocarbons.

Nomenclature of saturated hydrocarbons.

Isomerism.

4. Consolidation of knowledge and skills:

Page 38 No. 4-8, 13 exercise

5. Summing up the lesson: Frontal survey: according to the lecture.

6. Homework: Working from notes . §6 page 38 11-12 exercise

3. In addition to methane, natural gas contains many other hydrocarbons that are similar in structure and properties to methane. They are called saturated hydrocarbons or paraffins or alkanes. These hydrocarbons form a homologous series of saturated hydrocarbons: CH 4 - methane C 2 H 6 - ethane C 3 H 8 - propane C 4 H 10 - butane C 5 H 12 - pentane C 6 H 14 - hexane C 7 H 16 - heptane C 8 H 18 - octane C 9 H 20 - nonane C 10 H 22 – dec. Homologs are substances that are similar in structure and chemical properties, but differ from each other by a group of CH atoms 2 . General formula of homologues of the methane series: C p N 2p+2 where n is the number of carbon atoms.Carbon atoms, connecting with each other in a chain in a hydrocarbon molecule, form a zagzag, that is, the carbon chain is zigzag, and the reason for this is the tetrahedral direction of the valence bonds of the carbon atoms.

When bonds are broken, hydrocarbon molecules can become free radicals. When one hydrogen atom is removed, monovalent radicals are formed: CH 4 - methane - CH 3 methyl C 2 H 6 - ethane - C 2 H 5 - ethyl C 3 H 8 - propane - C 3 H 7 - propyl C 4 H 10 - butane - C 4 H 9 butyl. 5. There are several types of nomenclature: historical, rational, modern or international. The main one is the international systematic nomenclature or Geneva. Its basic principles were adopted at the international congress of chemists in Geneva in 1892.Basic Rules:A) The longest chain of carbon atoms is identified in the structural formula and numbered from the end where the branching is closest.B) the name of the substance is indicated by the number at which carbon atom the substituent group is located.C) When branching begins at carbon atoms equidistant from the main chain, numbering is carried out from the end to which the radical with a simpler structure is located closer.6. for the limiting ones, there is only 1 type of structural isomerism - chain or carbon skeleton isomerism.Give an example of butane.