Atoms are very small particles, their size ranges from one to five angstroms (denoted by Ao.). One angstrom is 10–10 meters. The size of a sugar crystal is approximately 1 mm; such a crystal is approximately 10 million times larger than any of its constituent atoms. To better understand how small atoms are, consider this example: if an apple is enlarged to the size globe, then the atom, enlarged by the same amount, will become the size of an average apple.
Despite such small sizes, atoms are quite complex particles. You will become familiar with the structure of atoms this year, but for now let’s just say that any atom consists of atomic nucleus and related electron shell , that is, it also represents a system.
Currently, just over a hundred types of atoms are known. Of these, about eighty are stable. And from these eighty types of atoms all the objects around us are built in all their infinite diversity.
One of the most important features atoms is their tendency to combine with each other. Most often this results in the formation of molecules.
A molecule can contain from two to several hundred thousand atoms. Moreover, small molecules (diatomic, triatomic...) can consist of identical atoms, while large ones, as a rule, consist of different atoms. Since a molecule consists of several atoms and these atoms are connected, a molecule is a system. In solids and liquids, molecules are connected to each other, but in gases they are not.
The bonds between atoms are called chemical bonds, and the bonds between molecules are intermolecular bonds.
Molecules connected to each other form substances.
Substances made up of molecules are called molecular substances. Thus, water consists of water molecules, sugar - from sucrose molecules, and polyethylene - from polyethylene molecules.
In addition, many substances consist directly of atoms or other particles and do not contain molecules. For example, aluminum, iron, diamond, glass, and table salt do not contain molecules. Such substances are called non-molecular.
In non-molecular substances, atoms and other chemical particles, as in molecules, are interconnected by chemical bonds. The division of substances into molecular and non-molecular is a classification of substances by type of structure.
Assuming that interconnected atoms retain a spherical shape, it is possible to construct three-dimensional models of molecules and non-molecular crystals. Examples of such models are shown in Fig. 1.1.
Most substances are usually found in one of three states of aggregation: solid, liquid or gaseous. When heated or cooled, molecular substances can change from one state of aggregation to another. Such transitions are shown schematically in Fig. 1.2.
The transition of a non-molecular substance from one state of aggregation to another may be accompanied by a change in the type of structure. Most often, this phenomenon occurs during the evaporation of non-molecular substances.
At melting, boiling, condensation and that similar phenomena, occurring with molecular substances, the molecules of the substances are not destroyed or formed. Only break or form intermolecular bonds. For example, ice turns into water when melting, and water when boiling turns into water vapor. In this case, water molecules are not destroyed, and, therefore, as a substance, water remains unchanged. Thus, in all three states of aggregation they are one and the same substance – water.
But not all molecular substances can exist in all three states of aggregation. Many of them when heated decompose, that is, they are transformed into other substances, while their molecules are destroyed. For example, cellulose (the main component wood and paper) does not melt when heated, but decomposes. Its molecules are destroyed, and completely different molecules are formed from the “fragments”.
So, molecular substance remains itself, that is, chemically unchanged, as long as its molecules remain unchanged.
But you know that molecules are in constant movement. And the atoms that make up molecules also move (oscillate). As the temperature increases, the vibrations of atoms in molecules increase. Can we say that the molecules remain completely unchanged? Of course not! What then remains unchanged? The answer to this question is in one of the following paragraphs.
Water. Water is the most famous and very widespread substance on our planet: the surface of the Earth is 3/4 covered with water, a person is 65% water, life is impossible without water, since in aqueous solution everything leaks cellular processes body. Water is a molecular substance. This is one of the few substances that natural conditions occurs in solid, liquid and gaseous states, and the only substance, for which each of these states has its own name. The structural features of water are caused by its unusual properties. For example, when water freezes, it increases in volume, so ice floats in its melt - liquid water, and highest density water is observed at 4 o C, so in winter large bodies of water do not freeze to the bottom. The Celsius temperature scale itself is based on the properties of water (0 o – freezing point, 100 o – boiling point). You will become familiar with the causes of these phenomena and the chemical properties of water in 9th grade. |
Iron- silvery-white, shiny, malleable metal. This is a non-molecular substance. Among metals, iron ranks second after aluminum in terms of abundance in nature and first place in importance for humanity. Together with another metal - nickel - it forms the core of our planet. Pure iron has no wide practical application. The famous Qutub Column, located in the vicinity of Delhi, is about seven meters high and weighs 6.5 tons, almost 2800 years old (it was erected in the 9th century BC) - one of the few examples of the use of pure iron (99.72 %); it is possible that it is the purity of the material that explains the durability and corrosion resistance of this structure. In the form of cast iron, steel and other alloys, iron is used in literally all branches of technology. Its valuable magnetic properties used in generators electric current and electric motors. Iron is a vital element for humans and animals, as it is part of blood hemoglobin. With its deficiency, tissue cells do not receive enough oxygen, which leads to very serious consequences. |
As you already know, atoms can be the same and different. How different atoms differ from each other in structure, you will soon find out, but for now let’s just say that different atoms are different chemical behavior , that is, their ability to connect with each other, forming molecules (or non-molecular substances).
In other words, chemical elements are the same types of atoms that were mentioned in the previous paragraph.
Each chemical element has its own name, for example: hydrogen, carbon, iron, and so on. In addition, each element is also assigned its own symbol. You see these symbols, for example, in the “Table of Chemical Elements” in the school chemistry classroom.
A chemical element is an abstract aggregate. This is the name for any number of atoms of a given type, and these atoms can be located anywhere, for example: one on Earth, and the other on Venus. The chemical element cannot be seen or touched with your hands. The atoms that make up a chemical element may or may not be bonded to each other. Consequently, a chemical element is neither a substance nor a material system.
Atoms and molecules. Atomically – molecular science. Molecular and non-molecular substances molecular structure
I. New material
This lecture will focus on the following concepts: “atom”, “molecule”, “substances of molecular and non-molecular structure”, “atomic-molecular doctrine”.
The ancient Greek philosopher Democritus 2500 years ago expressed the idea that all bodies in nature consist of tiny invisible, impenetrable, indivisible, ever-moving particles - atoms. The word “atom” in translation means “indivisible”. Later, in the Middle Ages, the doctrine of atoms was persecuted by religion, which hampered the development of science in general, and chemistry in particular.
The doctrine of molecules and atoms was developed in the mid-18th century by the great Russian scientist Mikhail Vasilyevich Lomonosov (1711 - 1765). He argued that bodies in nature consist of corpuscles (molecules), which include elements (atoms). The scientist insightfully explained the variety of substances by the combination of different atoms in molecules and the different arrangements of atoms in them. M.V. Lomonosov’s idea that some corpuscles (molecules) could consist of identical elements (atoms) was surprisingly true and bold for that time. The doctrine of atoms was further developed in the works of the famous English scientist John Dalton (1766 - 1844).
MOLECULES AND ATOMS
Is it possible to experimentally prove that molecules are made up of atoms?
The fact that atoms really exist is confirmed by many chemical reactions. So, for example, when passing direct current Gas collects through the water in one of the tubes of the device, in which the smoldering splinter flares up brightly. This is oxygen. In another tube it is collected twice more gas, which lights up from a lit splinter. This is hydrogen.
Diagram of an apparatus for water decomposition (Hoffmann apparatus)
This phenomenon can be explained as follows. The smallest particle of water - a molecule consists of 2 hydrogen atoms and one oxygen atom. When a direct current is passed through water, its molecules disintegrate and chemically indivisible particles are formed - atoms of oxygen and hydrogen. Then the atoms combine in twos, and from two water molecules one is formed - a diatomic oxygen molecule and two hydrogen.
Some ideas about atoms and molecules expressed by M.V. Lomonosov half a century before D. Dalton turned out to be more reliable and scientific. For example, an English scientist categorically denied the possibility of the existence of molecules consisting of identical atoms. His views had a negative impact on the development of chemistry. The doctrine of molecules and atoms was finally accepted only in 1860 at the World Congress of Chemists in Carlerue.
So what are molecules and atoms?
Molecules- the smallest particles of a substance, the composition and chemical properties of which are the same as those of of this substance. Molecules are the ultimate result of mechanical fragmentation of a substance.
Atoms- These are the smallest chemically indivisible particles that make up molecules. Molecules, unlike atoms, are chemically divisible particles.
Molecular substances
Molecular substances - these are substances whose smallest structural particles are molecules
Molecules - smallest particle a molecular substance capable of existing independently and preserving its chemical properties.
Molecular substances have low temperatures melting and boiling and are found under standard conditions in a solid, liquid or gaseous state.
For example: Water is liquid, tmelt = 0°C; tboil=100°С
Water is the most famous and very widespread substance on our planet: the surface of the Earth is 3/4 covered with water, a person is 65% water, life is impossible without water, since all cellular processes of the body take place in an aqueous solution. Water is a molecular substance. It is one of the few substances that naturally occurs in solid, liquid and gaseous states, and the only substance for which each of these states has its own name.
The structural features of water cause its unusual properties. For example, when water freezes, it increases in volume, so ice floats in its melt - liquid water, and the highest density of water is observed at 4 oC, so in winter large bodies of water do not freeze to the bottom. The Celsius temperature scale itself is based on the properties of water (0 o – freezing point, 100 o – boiling point). You will become more familiar with the reasons for these phenomena and the chemical properties of water later.
Non-molecular substances
Non-molecular substances - these are substances whose smallest structural particles are atoms or ions.
And he is an atom or group of atoms that has a positive or negative charge.
For example: Na+, Cl-.
Non-molecular substances are in a solid state of aggregation under standard conditions and have high temperatures melting and boiling.
For example: Salt- solid, melting point = 801°C; tboil=1465°С; Iron
Iron is a silvery-white, shiny, malleable metal. This is a non-molecular substance. Among metals, iron ranks second after aluminum in terms of abundance in nature and first place in importance for humanity. Together with another metal - nickel - it forms the core of our planet. Pure iron does not have wide practical applications. The famous Qutub Column, located in the vicinity of Delhi, is about seven meters high and weighs 6.5 tons, almost 2800 years old (it was erected in the 9th century BC) - one of the few examples of the use of pure iron (99.72 %); it is possible that it is the purity of the material that explains the durability and corrosion resistance of this structure.
In the form of cast iron, steel and other alloys, iron is used in literally all branches of technology. Its valuable magnetic properties are used in electric current generators and electric motors. Iron is a vital element for humans and animals, as it is part of blood hemoglobin. With its deficiency, tissue cells do not receive enough oxygen, which leads to very serious consequences.
Atomic-molecular science was developed and first applied in chemistry by the great Russian scientist Lomonosov. The essence of Lomonosov's teachings can be reduced to the following provisions.
1. All substances consist of “corpuscles” (as Lomonosov called molecules).
2. Molecules consist of “elements” (as Lomonosov called atoms).
3. Particles - molecules and atoms - are in continuous motion. Thermal state bodies are the result of the movement of their particles.
4. Molecules simple substances consist of identical atoms, molecules of complex substances are made of different atoms.
Atomistic theory was applied to chemistry by the English scientist John Dalton. At its core, Dalton's teaching repeats Lomonosov's teaching. At the same time, it develops it further, since Dalton first tried to establish atomic masses then known elements. However, Dalton denied the existence of molecules in simple substances, which is a step backward in comparison with Lomonosov’s teaching. According to Dalton, simple substances consist only of atoms, and only complex substances consist of “complex atoms” (in modern understanding- molecules). Dalton's denial of the existence of molecules of simple substances prevented further development chemistry. The atomic-molecular theory in chemistry was finally established only in the middle of the 19th century. A molecule is the smallest particle of a given substance that has its chemical properties. Chemical properties molecules are determined by its composition and chemical structure. Atom is the smallest particle chemical element, which is part of the molecules of simple and complex substances. The chemical properties of an element are determined by the structure of its atom. From this follows the definition of an atom, corresponding modern ideas: An atom is an electrically neutral particle consisting of a positively charged atomic nucleus and negatively charged electrons. According to modern concepts, substances in gaseous and vaporous states are made up of molecules. In the solid state, only substances whose crystal lattice has molecular structure.
The main provisions of the atomic-molecular doctrine can be formulated as follows:
- There are substances with molecular and non-molecular structure.
- There are gaps between the molecules, the sizes of which depend on the state of aggregation of the substance and temperature. The greatest distances exist between gas molecules. This explains their easy compressibility. Liquids where the spaces between the molecules are much smaller are more difficult to compress. IN solids The gaps between the molecules are even smaller, so they hardly shrink.
- Molecules are in continuous motion. The speed of movement of molecules depends on temperature. As temperature increases, the speed of molecular movement increases.
- Between molecules there are forces of mutual attraction and repulsion. IN to the greatest extent These forces are expressed in solids and least in gases.
- Molecules consist of atoms, which, like molecules, are in continuous motion.
- Atoms of one type differ from atoms of another type in mass and properties.
- During physical phenomena, molecules are preserved; during chemical phenomena, as a rule, they are destroyed.
- Substances with a molecular structure have molecules in the solid state at the nodes of crystal sieves. The bonds between molecules located at the sites of the crystal lattice are weak and break when heated. Therefore, substances with a molecular structure, as a rule, have low melting points.
- In substances with a non-molecular structure in the nodes crystal lattices there are atoms or other particles. There are strong chemical bonds between these particles, which require a lot of energy to break. Therefore, substances with a non-molecular structure have high melting points.
Explanation of physical and chemical phenomena from the point of view of atomic-molecular science. Physical and chemical phenomena receive an explanation from the standpoint of atomic-molecular theory. For example, the process of diffusion explains the ability of molecules (atoms, particles) of one substance to penetrate between molecules (atoms, particles) of another substance. This happens because molecules (atoms, particles) are in continuous motion and there are gaps between them. Essence chemical reactions is to destroy chemical bonds between atoms of some substances and in the rearrangement of atoms to form other substances.
II. Consolidation
1. Give answers to the following questions:
2. Name the ancient Greek philosopher who expressed the idea that all bodies in nature consist of tiny invisible, impenetrable, indivisible, ever-moving particles - atoms.
3. Name the great Russian scientist, the founder of the doctrine of molecules and atoms.
4. Define a molecule.
5. Define an atom.
6. What substances are classified as substances of molecular structure? Give examples of substances.
7. What substances are classified as substances of non-molecular structure? Give examples of substances.
8. What properties are characterized by substances of molecular structure?
9. What properties are characterized by substances of non-molecular structure?
10. How to explain physical and chemical phenomena from the point of view of atomic-molecular science?
A molecule is the smallest particle of a substance that determines its properties and is capable of independent existence. Molecules are built from atoms.
A substance (for example, sugar) can be ground in the finest mill and still each grain will consist of a huge number of identical sugar molecules and will retain all the properties of this substance known to us. Even if a substance is broken down into individual molecules, as happens when sugar is dissolved in water, the substance continues to exist and exhibit its properties (this is easy to verify by tasting the solution). This means that an independently existing sugar molecule is still a substance called “sugar” (even if very small amount this substance). But if you continue crushing further, you will have to destroy the molecules. And by destroying molecules or even taking away a couple of atoms from them (out of the three dozen that make up a sugar molecule!), we are already destroying the substance itself. Of course, atoms do not disappear anywhere - they begin to become part of some other molecules. But sugar as a substance ceases to exist - it turns into some other substance.
Substances are not eternal because their molecules are not eternal. But atoms are practically eternal. In each of us there are atoms that existed back in the time of dinosaurs. Or those who took part in the campaigns of Alexander the Great, or in the voyages of Columbus, or who visited the court of Ivan the Terrible.
Despite the fact that the molecules are very small, their structure can be elucidated by various physical and chemical methods. A pure substance consists of molecules of one type. If physical body contains molecules of several types, then we are dealing with a mixture of substances. The concepts of “pure” in chemistry and in everyday life are not the same. For example, when we say: “What fresh air!" - then we are actually inhaling a complex mixture of several gaseous substances. A chemist will say about forest air: “We need to work seriously to isolate from this mixture pure substances". It is interesting that a person could not exist in the atmosphere of any of them separately. Table 1-1 shows the ratio of these gaseous substances in fresh forest air.
Table 1-1. Compound atmospheric air in a pine forest.
In Table 1-1 nitrogen, oxygen, argon, etc. - these are separate substances. The substance nitrogen consists of molecules nitrogen, everyone known substance water - from molecules water, terpineol consists of molecules terpineol. The molecules of these substances can be very different - from the simplest, consisting of two or three atoms (nitrogen, oxygen, ozone, carbon dioxide) - to molecules consisting of many atoms (such molecules are found in living organisms). For example, terpineol, which is formed in coniferous trees and gives the air a smell of freshness.
This means that substances, as well as types of molecules, can be infinite set. No one can name the exact number of substances known to people Today. We can only roughly say that there are more than seven million such substances.
Atoms in molecules of different substances are bonded to each other in a strictly in a certain order, the establishment of which is one of the most interesting activities in the work of a chemist. The structure and composition of molecules can be described different ways, for example, as is done in Fig. 1-1, where the atoms are spherical. The ball sizes are physical meaning and roughly correspond relative sizes atoms. The same substances can be depicted differently - using chemical symbols. Since ancient times, each type of atom in chemistry has been assigned a symbol from Latin letters. Table 1-2 shows symbolic records of the substances shown in Fig. 1-1. Such symbolic notations are called chemical formulas.
Table 1-2. Chemical formulas substances from fig. 1-1. The number below the symbol shows how many atoms of a given type are contained in the molecule. This figure is called the index. By tradition, the index "1" is never written. For example, instead of C 1 O 2 they simply write: CO 2.
Rice. 1-1. Models of molecules and names of substances that make up forest air: 1 - nitrogen, 2 - oxygen, 3 - argon, 4 - carbon dioxide, 5 - water, 6 - ozone (formed from oxygen when lightning discharges), 7 - terpineol (excreted by coniferous trees).
There is a conditional division of substances into simple and complex. Molecules of simple substances consist of atoms of the same type. Examples: nitrogen, oxygen, argon, ozone. Molecules of complex substances are composed of two or more types of atoms: carbon dioxide, water, terpineol.
Often the physical body is made up of molecules of several different substances. Such a physical body is called a mixture. For example, air is a mixture of several simple and complex substances. Do not confuse a complex substance with a mixture. Complex substance, if it consists of molecules of only one type, it is not a mixture.
Lesson objectives:
- tell students about molecules and atoms and teach them to distinguish between them.
Lesson objectives:
Educational: explore new material on the topic “Molecules and Atoms”;
Developmental: promote the development of thinking and cognitive skills; mastering methods of synthesis and analysis;
Educational: fostering positive motivation for learning.
Key terms:
Molecule– an electrically neutral particle that consists of two or more atoms connected by covalent bonds; the smallest particle of a substance that has its properties.
Atom– the smallest chemically indivisible part of an element, which is the carrier of its properties; consists of electrons and an atomic nucleus. Various quantity different atoms connected by interatomic bonds form molecules.
Atomic nucleus – central part atom, in which more than 99.9% of its mass is concentrated.
3. Why are the particles that make up the substance?
4.How to explain the drying of clothes after washing?
5.Why solids made up of particles appear solid?
Molecules.
2.What are the names of the particles that make up molecules?
3.Describe an experiment that can be used to determine the size of a molecule.
4. Do molecules of one substance differ in its various states of aggregation?
5.What is an atom and what does it consist of
Homework.
Try an experiment at home to measure the size of the molecule of any substance.
Interesting to know that.
The concept of an atom as the smallest indivisible part of matter was first formulated by ancient Indian and ancient Greek philosophers. In the XVII and XVIII centuries chemists were able to experimentally confirm this idea, showing that some substances cannot be further broken down into their constituent elements by chemical methods. However, in late XIX- at the beginning of the 20th century, physicists discovered subatomic particles and the composite structure of the atom, and it became clear that the atom is not really “indivisible.”
At the international congress of chemists in Karlsruhe (Germany) in 1860, definitions of the concepts of molecule and atom were adopted. An atom is the smallest particle of a chemical element that is part of simple and complex substances.
Physics of atoms and molecules is a branch of physics that studies internal structure And physical properties atoms, molecules and their more complex associations (clusters), as well as physical phenomena during low-energy elementary acts of interaction between objects and elementary particles.
When studying the physics of atoms and molecules, the main ones are: experimental methods like spectroscopy and mass spectrometry with all their varieties, some types of chromatography, resonance methods and microscopy, theoretical methods quantum mechanics, statistical physics and thermodynamics. The physics of atoms and molecules is closely interconnected with molecular physics, in which the (collective) physical properties of bodies in various states of aggregation are studied based on consideration of their microscopic structure, as well as with some branches of chemistry.
Let's spend short excursion into the history of the development of atomic-molecular theory:
Bibliography
1.Lesson on the topic “Molecules and Atoms” by S.V. Gromov, I.A. Motherland, physics teachers.
2. Lesson on the topic “Structure of Matter” Fonin Ilya Aleksandrovich, Kamzeeva Elena Evgenievna, physics teacher, Municipal Educational Institution Gymnasium No. 8, Kazan.
3.G. Oster. Physics. Problem book. A beloved guide. - M.: Rosman, 1998.
4.Meyani A. Big Book experiments for schoolchildren. M.: “Rosmen”. 2004
5.Global Physics “Atoms and Molecules.”
Edited and sent by Borisenko I.N.
Worked on the lesson:
Gromov S.V.
Fonin I.A.