But if molecules from the same atoms differ so much, what a variety there must be among molecules from different atoms! Let's look again in the air - maybe we will find such molecules there too? Of course we will!
Do you know what molecules you exhale into the air? (Of course, not only you - all people and all animals.) Molecules of your old friend - carbon dioxide! Bubbles of carbon dioxide pleasantly tingle your tongue when you drink sparkling water or lemonade. Pieces of dry ice that are put in ice cream boxes are also made of such molecules; dry ice is solid carbon dioxide.
In a carbon dioxide molecule, two oxygen atoms are attached from opposite sides to one carbon atom. "Carbon" means "the one who gives birth to coal." But carbon gives birth to more than just coal. When you draw with a simple pencil, small flakes of graphite remain on the paper - they also consist of carbon atoms. Diamond and ordinary soot are “made” of them. Again the same atoms - and completely dissimilar substances!
When carbon atoms combine not only with each other, but also with “foreign” atoms, then so many different substances are born that it is difficult to count them! Especially many substances are born when carbon atoms combine with atoms of the lightest gas in the world - hydrogen. All these substances are called by a common name - hydrocarbons, but each hydrocarbon has its own name.
The simplest of the hydrocarbons is spoken of in the verses you know: “But we have gas in our apartment - this is it!” The name of the gas that burns in the kitchen is methane. The methane molecule has one carbon atom and four hydrogen atoms. In the flame of a kitchen burner, methane molecules are destroyed, a carbon atom combines with two oxygen atoms, and you get the already familiar carbon dioxide molecule. Hydrogen atoms also combine with oxygen atoms, and as a result, molecules of the most important and necessary substance in the world are obtained!
Molecules of this substance are also in the air - there are a lot of them there. By the way, to some extent you are also involved in this, because you exhale these molecules into the air along with carbon dioxide molecules. What is this substance? If you didn’t guess, breathe on the cold glass, and here it is in front of you - water!

Interesting:
The molecule is so tiny that if we lined up one hundred million water molecules one after another, then this whole line would easily fit between two adjacent rulers in your notebook. But scientists still managed to find out what a water molecule looks like. Here is her portrait. True, it looks like the head of a bear cub Winnie the Pooh! Look how you pricked up your ears! Of course, these are not ears, but two hydrogen atoms attached to the “head” - the oxygen atom. But jokes are jokes, but really - do these “ears on top” have anything to do with the extraordinary properties of water?

DEFINITION

Carbon dioxide(carbon monoxide (IV), carbon dioxide, carbon dioxide) under normal conditions is a colorless gas, heavier than air, thermally stable, and when compressed and cooled, it easily turns into a liquid and solid (“dry ice”) state.

It is poorly soluble in water, partially reacting with it.

The main carbon dioxide constants are given in the table below.

Table 1. Physical properties and density of carbon dioxide.

Carbon dioxide plays an important role in biological (photosynthesis), natural (greenhouse effect) and geochemical (dissolution in the oceans and formation of carbonates) processes. In large quantities, it enters the environment as a result of burning fossil fuels, rotting waste, etc.

Chemical composition and structure of the carbon dioxide molecule

The chemical composition of a carbon dioxide molecule is expressed by the empirical formula CO 2 . The carbon dioxide molecule (Fig. 1) is linear, which corresponds to the minimum repulsion of binding electron pairs, the length of the C=H bond is 0.116 nm, and its average energy is 806 kJ/mol. In the framework of the method of valence bonds, two σ-bonds С-О are formed by the sp-hybridized orbital of the carbon atom and 2p z - orbitals of oxygen atoms. The 2p x and 2p y orbitals of the carbon atom that do not participate in sp hybridization overlap with similar orbitals of oxygen atoms. In this case, two π-orbitals are formed, located in mutually perpendicular planes.

Rice. 1. The structure of the carbon dioxide molecule.

Due to the symmetrical arrangement of oxygen atoms, the CO 2 molecule is non-polar, therefore the dioxide is slightly soluble in water (one volume of CO 2 in one volume of H 2 O at 1 atm and 15 o C). The non-polarity of the molecule leads to weak intermolecular interactions and a low temperature of the triple point: t = -57.2 o C and P = 5.2 atm.

Brief description of the chemical properties and density of carbon dioxide

Chemically, carbon dioxide is inert, which is due to the high energy of the O=C=O bonds. With strong reducing agents at high temperatures, carbon dioxide exhibits oxidizing properties. With coal, it is reduced to carbon monoxide CO:

C + CO 2 \u003d 2CO (t \u003d 1000 o C).

Magnesium, ignited in air, continues to burn in an atmosphere of carbon dioxide:

CO 2 + 2Mg \u003d 2MgO + C.

Carbon monoxide (IV) partially reacts with water:

CO 2 (l) + H 2 O \u003d CO 2 × H 2 O (l) ↔ H 2 CO 3 (l).

Shows acidic properties:

CO 2 + NaOH dilute = NaHCO 2 ;

CO 2 + 2NaOH conc \u003d Na 2 CO 3 + H 2 O;

CO 2 + Ba(OH) 2 = BaCO 3 ↓ + H 2 O;

CO 2 + BaCO 3 (s) + H 2 O \u003d Ba (HCO 3) 2 (l).

When heated to a temperature above 2000 o C, carbon dioxide decomposes:

2CO 2 \u003d 2CO + O 2.

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

Carbon dioxide, carbon monoxide, carbon dioxide are all names for the same substance we know as carbon dioxide. So what are the properties of this gas, and what are its applications?

Carbon dioxide and its physical properties

Carbon dioxide is made up of carbon and oxygen. The formula for carbon dioxide is CO₂. In nature, it is formed during the combustion or decay of organic matter. In the air and mineral springs, the gas content is also quite high. in addition, humans and animals also release carbon dioxide when they exhale.

Rice. 1. Molecule of carbon dioxide.

Carbon dioxide is a completely colorless gas and cannot be seen. It also has no odor. However, with its high concentration, a person may develop hypercapnia, that is, suffocation. Lack of carbon dioxide can also cause health problems. As a result of a lack of this gas, the reverse state of suffocation can develop - hypocapnia.

If carbon dioxide is placed in conditions of low temperature, then at -72 degrees it crystallizes and becomes like snow. Therefore, carbon dioxide in the solid state is called "dry snow".

Rice. 2. Dry snow is carbon dioxide.

Carbon dioxide is 1.5 times denser than air. Its density is 1.98 kg / m³. The chemical bond in the carbon dioxide molecule is covalent polar. It is polar because oxygen has a higher electronegativity value.

An important concept in the study of substances is the molecular and molar mass. The molar mass of carbon dioxide is 44. This number is formed from the sum of the relative atomic masses of the atoms that make up the molecule. The values ​​of relative atomic masses are taken from the table of D.I. Mendeleev and rounded up to whole numbers. Accordingly, the molar mass of CO₂ = 12+2*16.

To calculate the mass fractions of elements in carbon dioxide, it is necessary to follow the formula for calculating the mass fractions of each chemical element in a substance.

n is the number of atoms or molecules.
A r is the relative atomic mass of a chemical element.
Mr is the relative molecular weight of the substance.
Calculate the relative molecular weight of carbon dioxide.

Mr(CO₂) = 14 + 16 * 2 = 44 w(C) = 1 * 12 / 44 = 0.27 or 27% Since carbon dioxide contains two oxygen atoms, n = 2 w(O) = 2 * 16 / 44 = 0.73 or 73%

Answer: w(C) = 0.27 or 27%; w(O) = 0.73 or 73%

Chemical and biological properties of carbon dioxide

Carbon dioxide has acidic properties, as it is an acidic oxide, and when dissolved in water forms carbonic acid:

CO₂+H₂O=H₂CO₃

It reacts with alkalis, resulting in the formation of carbonates and bicarbonates. This gas is non-flammable. Only some active metals, such as magnesium, burn in it.

When heated, carbon dioxide breaks down into carbon monoxide and oxygen:

2CO₃=2CO+O₃.

Like other acidic oxides, this gas easily reacts with other oxides:

СaO+Co₃=CaCO₃.

Carbon dioxide is a constituent of all organic substances. The circulation of this gas in nature is carried out with the help of producers, consumers and decomposers. In the process of life, a person produces about 1 kg of carbon dioxide per day. When we inhale, we get oxygen, but at this moment carbon dioxide is formed in the alveoli. At this point, an exchange occurs: oxygen enters the blood, and carbon dioxide goes out.

Carbon dioxide is produced during the production of alcohol. Also, this gas is a by-product in the production of nitrogen, oxygen and argon. The use of carbon dioxide is necessary in the food industry, where carbon dioxide acts as a preservative, and carbon dioxide in the form of a liquid is contained in fire extinguishers.

Rice. 3. Fire extinguisher.

What have we learned?

Carbon dioxide is a substance that under normal conditions is colorless and odorless. In addition to its common name, carbon dioxide, it is also called carbon monoxide or carbon dioxide.

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