Alkanes are examples of substances. Limit hydrocarbons

From a chemical point of view, alkanes are hydrocarbons, that is, the general formula of alkanes includes only carbon and hydrogen atoms. In addition to the fact that these compounds do not contain any functional groups, they are formed only by single bonds. Such hydrocarbons are called saturated.

Types of alkanes

All alkanes can be divided into two large groups:

aliphatic compounds. Their structure has the form of a linear chain, the general formula of aliphatic alkanes is C n H 2n+2, where n is the number of carbon atoms in the chain.
Cycloalkanes. These compounds have a cyclic structure, which causes a significant difference in their chemical properties from linear compounds. In particular, the structural formula of this type of alkanes determines the similarity of their properties with alkynes, that is, hydrocarbons with a triple bond between carbon atoms.

Electronic structure of aliphatic compounds

This group of alkanes may have either a linear or branched hydrocarbon chain. Their chemical activity is low compared to other organic compounds, since all bonds within the molecule are saturated.

The molecular formula of alkanes of the aliphatic type indicates that their chemical bond has sp 3 hybridization. This means that all four covalent bonds around the carbon atom are absolutely equal in terms of their characteristics (geometric and energy). With this type of hybridization, the electron shells of the s and p levels of carbon atoms have the same shape of an elongated dumbbell.

Between carbon atoms, the bond in the chain is covalent, and between carbon and hydrogen it is partially polarized, while the electron density is drawn to carbon, as to an element more electronegative.

It follows that only C-C and C-H bonds exist in their molecules. The former are formed as a result of the overlap of two electronic hybridized sp 3 orbitals of two carbon atoms, and the latter are formed as a result of the overlap of the s orbital of hydrogen and the sp 3 orbital of carbon. The C-C bond length is 1.54 angstroms and the C-H bond length is 1.09 angstroms.

Geometry of the methane molecule

Methane is the simplest alkane, consisting of only one carbon atom and four hydrogen atoms.

Due to the energy equality of its three 2p and one 2s orbitals, obtained as a result of sp 3 hybridization, all orbitals in space are located at the same angle to each other. It is equal to 109.47°. As a result of such a molecular structure, a similarity of a triangular equilateral pyramid is formed in space.

Simple alkanes

The simplest alkane is methane, which consists of one carbon atom and four hydrogen atoms. Following methane in the alkane series, propane, ethane and butane are formed by three, two and four carbon atoms, respectively. Starting with five carbons in the chain, compounds are named according to the IUPAC nomenclature.

A table with the formulas of alkanes and their names is given below:

With the loss of one hydrogen atom, an alkane molecule forms an active radical, the end of which changes from "an" to "yl", for example, ethane C 2 H 6 - ethyl C 2 H 5. The structural formula of ethane alkane is shown in the photo.

Nomenclature of organic compounds

The rules for determining the names of alkanes and compounds based on them are established by the international IUPAC nomenclature. For organic compounds, the following rules apply:

The name of a chemical compound is based on the name of its longest chain of carbon atoms.
The numbering of carbon atoms should start from the end, closer to which the chain branching begins.
If there are two or more carbon chains of the same length in the compound, then the one that has the fewest radicals is chosen as the main one, and they have a simpler structure.
If there are two or more identical groups of radicals in the molecule, then the corresponding prefixes are used in the name of the compound, which double, triple, and so on, the names of these radicals. For example, "3,5-dimethyl" is used instead of "3-methyl-5-methyl".
All radicals are written in alphabetical order in the common name of the compound, and prefixes are not taken into account. The last radical is written together with the name of the chain itself.
The numbers reflecting the numbers of radicals in the chain are separated from the names by a hyphen, and the numbers themselves are written separated by commas.

Compliance with the rules of IUPAC nomenclature makes it easy to determine the molecular formula of an alkane by, for example, 2,3-dimethylbutane has the following form.

Physical properties

The physical properties of alkanes largely depend on the length of the carbon chain forming a particular compound. The main properties are the following:

The first four representatives, according to the general formula of alkanes, are in a gaseous state under normal conditions, that is, they are butane, methane, propane and ethane. As for pentane and hexane, they already exist in the form of liquids, and starting from seven carbon atoms, alkanes are solids.
With an increase in the length of the carbon chain, the density of the compound also increases, as well as its first-order phase transition temperatures, that is, the melting and boiling points.
Since the polarity of the chemical bond in the formula of the substance of alkanes is insignificant, they do not dissolve in polar liquids, for example, in water.
Accordingly, they can be used as good solvents for compounds such as non-polar fats, oils and waxes.
The home gas stove uses a mixture of alkanes rich in the third member of the chemical series - propane.
Oxygen combustion of alkanes releases a large amount of energy in the form of heat, so these compounds are used as a combustible fuel.

Chemical properties

Due to the presence of stable bonds in the molecules of alkanes, their reactivity in comparison with other organic compounds is low.

Alkanes practically do not react with ionic and polar chemical compounds. They behave inertly in solutions of acids and bases. Alkanes react only with oxygen and halogens: in the first case, we are talking about oxidation processes, in the second, about substitution processes. They also show some chemical activity in reactions with transition metals.

In all these chemical reactions, the branching of the carbon chain of alkanes, that is, the presence of radical groups in them, plays an important role. The more of them, the stronger the change in the ideal angle between bonds 109.47° in the spatial structure of the molecule, which leads to the creation of stresses inside it and, as a result, increases the chemical activity of such a compound.

The reaction of simple alkanes with oxygen occurs according to the following scheme: C n H 2n+2 + (1.5n+0.5)O 2 → (n+1)H 2O+ nCO 2 .

An example of a reaction with chlorine is shown in the photo below.

The danger of alkanes for nature and man

Heptane, pentane, and hexane are highly flammable liquids and are hazardous to both the environment and human health because they are toxic.

DEFINITION

Alkanes- saturated (aliphatic) hydrocarbons, the composition of which is expressed by the formula C n H 2 n +2.

Alkanes form a homologous series, each chemical compound of which differs in composition from the next and the previous one by the same number of carbon and hydrogen atoms - CH 2, and the substances included in the homologous series are called homologues. The homologous series of alkanes is presented in table 1.

Table 1. Homologous series of alkanes.

In alkane molecules, primary (i.e., linked by one bond), secondary (i.e., bonded by two bonds), tertiary (i.e., bonded by three bonds) and quaternary (i.e., bonded by four bonds) carbon atoms are distinguished.

C 1 H3 - C 2 H 2 - C 1 H 3 (1 - primary, 2 - secondary carbon atoms)

CH 3 -C 3 H (CH 3) - CH 3 (3-tertiary carbon atom)

CH 3 - C 4 (CH 3) 3 - CH 3 (4-quaternary carbon atom)

Alkanes are characterized by structural isomerism (isomerism of the carbon skeleton). So, pentane has the following isomers:

CH 3 -CH 2 -CH 2 -CH 2 -CH 3 (pentane)

CH 3 -CH (CH 3) -CH 2 -CH 3 (2-methylbutane)

CH 3 -C (CH 3) 2 -CH 3 (2,2 - dimethylpropane)

For alkanes, starting with heptane, optical isomerism is characteristic.

Carbon atoms in saturated hydrocarbons are in sp 3 hybridization. The angles between bonds in alkane molecules are 109.5.

Chemical properties of alkanes

Under normal conditions, alkanes are chemically inert - they do not react with either acids or alkalis. This is due to the high strength of C-C and C-H bonds. Nonpolar C-C and C-H bonds can only be cleaved homolytically by active free radicals. Therefore, alkanes enter into reactions proceeding according to the mechanism of radical substitution. In a radical reaction, first of all, hydrogen atoms are replaced at tertiary, then at secondary and primary carbon atoms.

Radical substitution reactions have a chain character. The main stages: the nucleation (initiation) of the chain (1) - occurs under the action of UV radiation and leads to the formation of free radicals, the growth of the chain (2) - occurs due to the detachment of a hydrogen atom from the alkane molecule; chain termination (3) occurs when two identical or different radicals collide.

X:X → 2X . (1)

R:H+X . → HX+R . (2)

R . + X:X → R:X + X . (2)

R . + R . → R:R (3)

R . + X . → R:X (3)

X . + X . → X:X (3)

Halogenation. When alkanes interact with chlorine and bromine under the action of UV radiation or high temperature, a mixture of products from mono- to polyhalo-substituted alkanes is formed:

CH 3 Cl + Cl 2 = CH 2 Cl 2 + HCl (dichloromethane)

CH 2 Cl 2 + Cl 2 = CHCl 3 + HCl (trichloromethane)

CHCl 3 + Cl 2 = CCl 4 + HCl (tetrachloromethane)

Nitration (Konovalov's reaction). Under the action of dilute nitric acid on alkanes at 140C and low pressure, a radical reaction occurs:

CH 3 -CH 3 + HNO 3 \u003d CH 3 -CH 2 -NO 2 (nitroethane) + H 2 O

Sulfochlorination and sulfoxidation. Direct sulfonation of alkanes is difficult and is most often accompanied by oxidation, resulting in the formation of alkanesulfonyl chlorides:

R-H + SO 2 + Cl 2 → R-SO 3 Cl + HCl

The sulfoxidation reaction proceeds similarly, only in this case alkane sulfonic acids are formed:

R-H + SO 2 + ½ O 2 → R-SO 3 H

Cracking- a radical rupture of C-C bonds. Occurs when heated and in the presence of catalysts. When higher alkanes are cracked, alkenes are formed; when methane and ethane are cracked, acetylene is formed:

C 8 H 18 \u003d C 4 H 10 (butane) + C 3 H 8 (propane)

2CH 4 \u003d C 2 H 2 (acetylene) + 3H 2

Oxidation. The mild oxidation of methane with atmospheric oxygen can produce methanol, formic aldehyde, or formic acid. In air, alkanes burn to carbon dioxide and water:

C n H 2 n + 2 + (3n + 1) / 2 O 2 \u003d nCO 2 + (n + 1) H 2 O

Physical properties of alkanes

Under normal conditions, C 1 -C 4 - gases, C 5 -C 17 - liquids, starting with C 18 - solids. Alkanes are practically insoluble in water, but highly soluble in non-polar solvents, such as benzene. So, methane CH 4 (marsh, mine gas) is a colorless and odorless gas, highly soluble in ethanol, ether, hydrocarbons, but poorly soluble in water. Methane is used as a high-calorie fuel in the composition of natural gas, as a raw material for the production of hydrogen, acetylene, chloroform and other organic substances on an industrial scale.

Propane C 3 H 8 and butane C 4 H 10 are gases used in everyday life as balloon gases due to their easy liquefaction. Propane is used as an automotive fuel because it is more environmentally friendly than gasoline. Butane is a raw material for the production of 1,3-butadiene, which is used in the production of synthetic rubber.

Obtaining alkanes

Alkanes are obtained from natural sources - natural gas (80-90% - methane, 2-3% - ethane and other saturated hydrocarbons), coal, peat, wood, oil and mountain wax.

Allocate laboratory and industrial methods for obtaining alkanes. In industry, alkanes are obtained from bituminous coal (1) or by the Fischer-Tropsch reaction (2):

nC + (n+1)H 2 = C n H 2 n +2 (1)

nCO + (2n+1)H 2 = C n H 2 n +2 + H 2 O (2)

The laboratory methods for obtaining alkanes include: hydrogenation of unsaturated hydrocarbons when heated and in the presence of catalysts (Ni, Pt, Pd) (1), interaction of water with organometallic compounds (2), electrolysis of carboxylic acids (3), decarboxylation reactions (4) and Wurtz (5) and in other ways.

R 1 -C≡C-R 2 (alkyne) → R 1 -CH \u003d CH-R 2 (alkene) → R 1 -CH 2 - CH 2 -R 2 (alkane) (1)

R-Cl + Mg → R-Mg-Cl + H 2 O → R-H (alkane) + Mg(OH)Cl (2)

CH 3 COONa ↔ CH 3 COO - + Na +

2CH 3 COO - → 2CO 2 + C 2 H 6 (ethane) (3)

CH 3 COONa + NaOH → CH 4 + Na 2 CO 3 (4)

R 1 -Cl + 2Na + Cl-R 2 → 2NaCl + R 1 -R 2 (5)

Examples of problem solving

EXAMPLE 1

Exercise

Determine the mass of chlorine required for chlorination in the first stage of 11.2 liters of methane.

Decision

Let us write the reaction equation for the first stage of methane chlorination (i.e., in the halogenation reaction, only one hydrogen atom is replaced, resulting in the formation of a monochlorine derivative):

CH 4 + Cl 2 \u003d CH 3 Cl + HCl (chloromethane)

Find the amount of methane substance:

v (CH 4) \u003d V (CH 4) / V m

v (CH 4) \u003d 11.2 / 22.4 \u003d 0.5 mol

According to the reaction equation, the number of moles of chlorine and the number of moles of methane are equal to 1 mole, therefore, the practical number of moles of chlorine and methane will also be the same and will be equal to:

v (Cl 2) \u003d v (CH 4) \u003d 0.5 mol

Knowing the amount of chlorine substance, you can find its mass (which is posed in the question of the problem). The mass of chlorine is calculated as the product of the amount of chlorine substance and its molar mass (molecular mass is 1 mole of chlorine; molecular mass is calculated using the table of chemical elements of D.I. Mendeleev). The mass of chlorine will be equal to:

m (Cl 2) \u003d v (Cl 2) × M (Cl 2)

m(Cl 2) \u003d 0.5 × 71 \u003d 35.5 g

Answer

The mass of chlorine is 35.5 g

I. ALKANE (saturated hydrocarbons, paraffins)

Alkanes are aliphatic (acyclic) saturated hydrocarbons in which carbon atoms are linked together by simple (single) bonds into unbranched or branched chains.

Alkanes- the name of saturated hydrocarbons according to the international nomenclature.
Paraffins- a historically established name reflecting the properties of these compounds (from lat. parrum affinis- having little affinity, inactive).
limiting, or rich, these hydrocarbons are named in connection with the complete saturation of the carbon chain with hydrogen atoms.

The simplest representatives of alkanes:

When comparing these compounds, it is clear that they differ from each other by a group -CH 2 - (methylene). Adding another group to propane -CH 2 -, we get butane C 4 H 10, then alkanes C 5 H 12, C 6 H 14 etc.

Now you can derive the general formula for alkanes. The number of carbon atoms in the series of alkanes will be taken as n , then the number of hydrogen atoms will be 2n+2 . Therefore, the composition of alkanes corresponds to the general formula C n H 2n+2.
Therefore, the following definition is often used:

Alkanes- hydrocarbons, the composition of which is expressed by the general formula C n H 2n+2, where n is the number of carbon atoms.

II. The structure of alkanes

Chemical structure(the order of connection of atoms in molecules) of the simplest alkanes - methane, ethane and propane - show their structural formulas. From these formulas it can be seen that there are two types of chemical bonds in alkanes:
S–S and S–N.
The C–C bond is covalent nonpolar. The C–H bond is covalent, weakly polar, because carbon and hydrogen are close in electronegativity (2.5 for carbon and 2.1 for hydrogen). The formation of covalent bonds in alkanes due to the common electron pairs of carbon and hydrogen atoms can be shown using electronic formulas:

Electronic and structural formulas reflect chemical structure, but give no idea of spatial structure of molecules, which significantly affects the properties of the substance.
Spatial structure, i.e. the mutual arrangement of the atoms of a molecule in space depends on the direction of the atomic orbitals (AO) of these atoms. In hydrocarbons, the main role is played by the spatial orientation of the atomic orbitals of carbon, since the spherical 1s-AO of the hydrogen atom is devoid of a definite orientation.
The spatial arrangement of carbon AOs, in turn, depends on the type of its hybridization. The saturated carbon atom in alkanes is bonded to four other atoms. Therefore, its state corresponds to sp 3 hybridization. In this case, each of the four sp 3 -hybrid carbon AOs participates in axial (σ-) overlap with the s-AO of hydrogen or with the sp 3 -AO of another carbon atom, forming σ-bonds С-Н or С-С.

Four σ-bonds of carbon are directed in space at an angle of 109 about 28 ", which corresponds to the smallest repulsion of electrons. Therefore, the molecule of the simplest representative of alkanes - methane CH 4 - has the shape of a tetrahedron, in the center of which there is a carbon atom, and at the vertices - hydrogen atoms:

The bond angle H-C-H is 109 o 28". The spatial structure of methane can be shown using volumetric (scale) and ball-and-stick models.

For recording, it is convenient to use the spatial (stereochemical) formula.

In the molecule of the next homologue - ethane C 2 H 6 - two tetrahedral sp 3 carbon atoms form a more complex spatial structure:

2. If in molecules of the same composition and the same chemical structure, a different mutual arrangement of atoms in space is possible, then there is spatial isomerism (stereoisomerism). In this case, the use of structural formulas is not enough, and molecular models or special formulas - stereochemical (spatial) or projection - should be used.
Alkanes, starting from ethane H 3 C–CH 3, exist in various spatial forms ( conformations) caused by intramolecular rotation along the C–C σ-bonds and exhibit the so-called rotational (conformational) isomerism.
The rotational isomers of a molecule are its energetically unequal states. Their interconversion occurs quickly and constantly as a result of thermal motion. Therefore, rotational isomers cannot be isolated individually, but their existence has been proven by physical methods. Some conformations are more stable (energetically favorable) and the molecule stays in such states for a longer time.

3. In addition, if there is a carbon atom in the molecule associated with 4 different substituents, another type of spatial isomerism is possible -optical isomerism.
For example:

then the existence of two compounds with the same structural formula, but differing in spatial structure, is possible. The molecules of such compounds relate to each other as an object and its mirror image and are spatial isomers.
Isomerism of this type is called optical, isomers - optical isomers or optical antipodes:

Molecules of optical isomers are incompatible in space (like left and right hands), they lack a plane of symmetry.
Thus,
Optical isomers have the same physical and chemical properties, but differ in their relationship to polarized light. Such isomers have optical activity (one of them rotates the plane of polarized light to the left, and the other - to the same angle to the right). Differences in chemical properties are observed only in reactions with optically active reagents.
Optical isomerism is manifested in organic substances of various classes and plays a very important role in the chemistry of natural compounds.

One of the first types of chemical compounds studied in the school curriculum in organic chemistry are alkanes. They belong to the group of saturated (otherwise - aliphatic) hydrocarbons. Their molecules contain only single bonds. Carbon atoms are characterized by sp³ hybridization.

Homologues are chemical substances that have common properties and chemical structure, but differ by one or more CH2 groups.

In the case of methane CH4, the general formula for alkanes can be given: CnH (2n+2), where n is the number of carbon atoms in the compound.

Here is a table of alkanes, in which n is in the range from 1 to 10.

Isomerism of alkanes

Isomers are those substances whose molecular formula is the same, but the structure or structure is different.

The class of alkanes is characterized by 2 types of isomerism: carbon skeleton and optical isomerism.

Let us give an example of a structural isomer (i.e., a substance that differs only in the structure of the carbon skeleton) for butane C4H10.

Optical isomers are called such 2 substances, the molecules of which have a similar structure, but cannot be combined in space. The phenomenon of optical or mirror isomerism occurs in alkanes, starting with heptane C7H16.

To give the alkane the correct name, use the IUPAC nomenclature. To do this, use the following sequence of actions:

According to the above plan, let's try to give a name to the next alkane.

Under normal conditions, unbranched alkanes from CH4 to C4H10 are gaseous substances, from C5H12 to C13H28 they are liquid and have a specific odor, all subsequent ones are solid. It turns out that as the length of the carbon chain increases, the boiling and melting points increase. The more branched the structure of an alkane, the lower the temperature at which it boils and melts.

Gaseous alkanes are colorless. And also all representatives of this class cannot be dissolved in water.

Alkanes having a state of aggregation of a gas can burn, while the flame will either be colorless or have a pale blue tint.

Chemical properties

Under normal conditions, alkanes are rather inactive. This is explained by the strength of the σ-bonds between the C-C and C-H atoms. Therefore, it is necessary to provide special conditions (for example, a fairly high temperature or light) to make the chemical reaction possible.

Substitution reactions

Reactions of this type include halogenation and nitration. Halogenation (reaction with Cl2 or Br2) occurs when heated or under the influence of light. During the reaction proceeding sequentially, haloalkanes are formed.

For example, you can write the reaction of chlorination of ethane.

Bromination will proceed in a similar manner.

Nitration is a reaction with a weak (10%) solution of HNO3 or with nitric oxide (IV) NO2. Conditions for carrying out reactions - temperature 140 °C and pressure.

C3H8 + HNO3 = C3H7NO2 + H2O.

As a result, two products are formed - water and an amino acid.

Decomposition reactions

Decomposition reactions always require a high temperature. This is necessary to break bonds between carbon and hydrogen atoms.

So, when cracking temperature required between 700 and 1000 °C. During the reaction, -C-C- bonds are destroyed, a new alkane and alkene are formed:

C8H18 = C4H10 + C4H8

An exception is the cracking of methane and ethane. As a result of these reactions, hydrogen is released and alkyne acetylene is formed. Prerequisite is heating up to 1500 °C.

C2H4 = C2H2 + H2

If you exceed the temperature of 1000 ° C, you can achieve pyrolysis with a complete rupture of bonds in the compound:

During the pyrolysis of propyl, carbon C was obtained, and hydrogen H2 was also released.

Dehydrogenation reactions

Dehydrogenation (hydrogen elimination) occurs differently for different alkanes. The reaction conditions are a temperature in the range from 400 to 600 ° C, as well as the presence of a catalyst, which can be nickel or platinum.

From a compound with 2 or 3 C atoms in the carbon skeleton, an alkene is formed:

C2H6 = C2H4 + H2.

If there are 4-5 carbon atoms in the chain of the molecule, then after dehydrogenation, alkadiene and hydrogen will be obtained.

C5H12 = C4H8 + 2H2.

Starting with hexane, during the reaction, benzene or its derivatives are formed.

C6H14 = C6H6 + 4H2

We should also mention the conversion reaction carried out for methane at a temperature of 800 °C and in the presence of nickel:

CH4 + H2O = CO + 3H2

For other alkanes, the conversion is uncharacteristic.

Oxidation and combustion

If an alkane heated to a temperature of not more than 200 ° C interacts with oxygen in the presence of a catalyst, then the products obtained will differ depending on other reaction conditions: these may be representatives of the classes of aldehydes, carboxylic acids, alcohols or ketones.

In the case of complete oxidation, the alkane burns to the final products - water and CO2:

C9H20 + 14O2 = 9CO2 + 10H2O

If there is insufficient oxygen during oxidation, the end product will be coal or CO instead of carbon dioxide.

Carrying out isomerization

If a temperature of about 100-200 degrees is provided, a rearrangement reaction becomes possible for unbranched alkanes. The second mandatory condition for isomerization is the presence of an AlCl3 catalyst. In this case, the structure of the molecules of the substance changes and its isomer is formed.

Significant the share of alkanes is obtained by separating them from natural raw materials. Most often, natural gas is processed, the main component of which is methane, or oil is subjected to cracking and rectification.

You should also remember about the chemical properties of alkenes. In grade 10, one of the first laboratory methods studied in chemistry lessons is the hydrogenation of unsaturated hydrocarbons.

C3H6 + H2 = C3H8

For example, as a result of the addition of hydrogen to propylene, a single product is obtained - propane.

Using the Wurtz reaction, alkanes are obtained from monohaloalkanes, in the structural chain of which the number of carbon atoms is doubled:

2CH4H9Br + 2Na = C8H18 + 2NaBr.

Another way to obtain is the interaction of a salt of a carboxylic acid with an alkali when heated:

C2H5COONa + NaOH = Na2CO3 + C2H6.

In addition, methane is sometimes produced in an electric arc (C + 2H2 = CH4) or by reacting aluminum carbide with water:

Al4C3 + 12H2O = 3CH4 + 4Al(OH)3.

Alkanes are widely used in industry as a low cost fuel. And they are also used as raw materials for the synthesis of other organic substances. For this purpose, methane is usually used, which is necessary for and synthesis gas. Some other saturated hydrocarbons are used to obtain synthetic fats, and also as a base for lubricants.

For the best understanding of the topic "Alkanes", more than one video lesson has been created, in which topics such as the structure of matter, isomers and nomenclature are discussed in detail, as well as the mechanisms of chemical reactions are shown.

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Alkanes - the name of saturated hydrocarbons according to the international nomenclature. Paraffins are the historically preserved name for saturated hydrocarbons.

In the molecules of these compounds, all valence bonds of carbon and hydrogen are completely saturated. That is why these hydrocarbons are not capable of addition reactions. In this regard, this class of hydrocarbons can be defined as follows:
Hydrocarbons with the general formula C n H 2n+2 that do not add hydrogen and other elements are called saturated hydrocarbons or alkanes (paraffins).

The simplest representative of saturated hydrocarbons is methane.

The structure of the methane molecule.

The molecular formula of methane is CH 4 .
Since hybridization is involved s- electron and three p- electron, then this type of it is called sp 3 - hybridization.
Valence angle: 109 degrees.

Methane homologues.

There are many hydrocarbons similar to methane, i.e. methane homologues (Greek "homolog" - similar). Molecules contain two, three, four or more carbon atoms. Each subsequent hydrocarbon differs from the previous one by a group of atoms CH 2. For example, if you mentally add a CH 2 group to a CH 4 methane molecule (the CH 2 group is called a homological difference), then the next hydrocarbon of the methane series is obtained - ethane C 2 H 6, etc.

The homologous rad 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 - Nonan

Isomerism and nomenclature.

To compile the names of saturated branched chain hydrocarbons, it is assumed that in all molecules the hydrogen atoms are replaced by various radicals. To determine the names of a given hydrocarbon, a certain order is followed:

The longest carbon chain is chosen in the formula and the symbols of carbon atoms are numbered, starting from the end of the chain, to which the branching is closer.
They name the radicals (starting with the simplest) and use numbers to indicate the place at the numbered carbon atoms. If the same carbon atom has two identical radicals, then the number is repeated twice. The number of identical radicals is indicated using numbers in Greek ("di" - two, "three" - three, "tetra" - four, etc.)
The full name of this hydrocarbon is given by the number of carbon atoms in the numbered chain.

Finding in nature.

The simplest representative of saturated hydrocarbons is methane- is formed in nature as a result of the decomposition of the remains of plant and animal organisms without air access. This explains the appearance of gas bubbles in swampy water bodies. Sometimes methane is released from coal seams and accumulates in mines. Methane makes up the bulk of natural gas ( 80 -97% ). It is also found in gases released during oil production. The composition of natural gas and petroleum gases also includes ethane C 2 H 6 , propane C 3 H 8 , butane C 4 H 10 and some others. Gaseous, liquid and solid saturated hydrocarbons are contained in oil.

physical properties.

Methane is a colorless and odorless gas, almost 2 times lighter than air, slightly soluble in water. Ethane, propane, butane are gases under normal conditions, pentane to pentadecane are liquids, and the following homologues are solids.
With an increase in the relative molecular masses of saturated hydrocarbons, their boiling and melting points naturally increase.