Conductivity
Superconductivity theory
During the formation of crystal lattices of solids from atoms of various substances, valence electrons located in the outer orbits of atoms interact with each other in different ways and, as a result, behave differently (see strip
theory of solid-state superconductivity and theory
molecular orbitals). Thus, the freedom of valence electrons to move inside a substance is determined by its molecular crystal structure. On the whole, according to the electrically conductive properties, all substances can (with some degree of convention) be subdivided into three categories, each of which has pronounced characteristics of the behavior of valence electrons under the influence of an external electric field.
Conductors
In some substances, valence electrons move freely between atoms. First of all, this category includes metals in which the electrons of the outer shells are literally in the "common property" of the atoms of the crystal lattice (see.
chemical bonds and electronic theory of conduction).
If you apply an electric voltage to such a substance (for example, connect the poles of a storage battery to its two ends), the electrons will begin an unobstructed, ordered movement in the direction of the south pole of the potential difference, thereby creating an electric current. Conductive substances of this kind are usually called conductors. The most common conductors in technology are, of course, metals, primarily copper and aluminum, which have a minimum electrical resistance and are quite widespread in earthly nature. It is from them that high-voltage electrical cables and household electrical wiring are mainly made. There are other types of materials with good electrical conductivity, such as saline, alkaline and acid solutions, as well as plasma and some types of long organic molecules.
In this regard, it is important to remember that electrical conductivity can be due to the presence in a substance not only of free electrons, but also of free positively and negatively charged ions of chemical compounds. In particular, even in ordinary tap water, so many different salts are dissolved, decomposing when dissolved into negatively charged cations and positively charged anions, that water (even fresh) is a very good conductor, and this should not be forgotten when working with electrical equipment in conditions of high humidity - otherwise, you can get a very noticeable electric shock.
Insulators
In many other substances (in particular, glass, porcelain, plastics), electrons are firmly attached to atoms or molecules and
not capable of free movement under the influence of an external voltage applied. These materials are called insulators.
Most often in modern technology, various plastics are used as electrical insulators. In fact, any plastic consists of polymer molecules - that is, very long chains of organic (hydrogen-carbon) compounds - which, moreover, form complex and very strong interweaving. The easiest way to imagine the structure of the polymer is in the form of a plate of tangled and stuck together long and thin noodles. In such materials, electrons are firmly attached to their ultra-long molecules and are unable to leave them under the influence of external stress. Amorphous substances such as glass, porcelain or rubber, which do not have a rigid crystalline structure, also have good insulating properties. They are also often used as electrical insulators.
Both conductors and insulators play an important role in our technogenic civilization, which uses electricity as the main means of transmitting energy over a distance. Electricity travels through conductors from power plants to our homes and to all kinds of industrial enterprises, and insulators ensure our safety, protecting us from the destructive consequences of direct contact of the human body with high electrical voltage.
Semiconductors
Finally, there is a small category of chemical elements that occupy an intermediate position between metals and insulators (the most famous of them are silicon and germanium). In the crystal lattices of these substances, all the valence electrons, at first glance, are linked by chemical bonds and free electrons to ensure electrical conductivity, it would seem, should not remain. However, in reality, the situation looks somewhat different, since some of the electrons are knocked out of their outer orbits as a result of thermal motion due to insufficient energy of their binding with atoms. As a result, at temperatures above absolute zero, they still have a certain electrical conductivity under the influence of external voltage. Their conductivity coefficient is rather low (the same silicon conducts an electric current millions of times worse than copper), but they still conduct some kind of current, albeit insignificant. Such substances are called semiconductors.
As it turned out as a result of research, electrical conductivity in semiconductors, however, is due not only to the movement of free electrons (the so-called n-conductivity due to the directional movement of negatively charged particles). There is also a second mechanism of electrical conductivity, which is quite unusual. When an electron is released from the crystal lattice of a semiconductor due to thermal motion, a so-called hole is formed in its place - a positively charged cell of the crystal structure, which can at any time be occupied by a negatively charged electron that has jumped into it from the outer orbit of a neighboring atom, where, in turn , a new positively charged hole is formed. Such a process can continue for an arbitrarily long time, and it will look from the outside (on a macroscopic scale) that the electric current under external voltage is not due to the movement of electrons (which just jump from the outer orbit of one atom to the outer orbit of a neighboring atom), but directed migration of a positively charged hole (electron deficit) towards the negative pole of the applied potential difference. As a result, a second type of conductivity is also observed in semiconductors (the so-called hole, or p-conductivity), which is, of course, also caused by the movement of negatively charged electrons, but from the point of view of the macroscopic properties of the substance, it is represented by a directed current of positively charged holes to the negative pole.
The hole conduction phenomenon is most easily illustrated with the example of a traffic jam. As the car stuck in it moves forward, free space is formed in its place, which is immediately occupied by the next car, the place of which is immediately taken by the third car, etc. This process can be imagined in two ways: you can describe the rare advance of individual cars from among those standing in a long traffic jam; it is easier, however, to characterize the situation from the point of view of episodic movement in the opposite direction of a few voids between cars stuck in a traffic jam. It is guided by a similar analogy that physicists talk about hole conduction, conditionally taking for granted that an electric current is conducted not due to the movement of numerous negatively charged electrons that rarely move from their place, but due to the movement in the opposite direction of positively charged voids in the outer orbits of semiconductor atoms, which they agreed to call holes. Thus, the dualism of electron-hole conduction is purely conditional, since from a physical point of view, the current in semiconductors is in any case due exclusively to the directional motion of electrons.
Semiconductors have found wide practical application in modern radio electronics and computer technologies precisely because their conductive properties are easily and accurately controlled by changing external conditions.
electronic theory of conduction
The electrical conductivity of solids is due to the collective directional motion of free electrons
During the formation of crystal lattices of solids from atoms of various substances, valence electrons located in the outer orbits of atoms interact with each other in different ways and, as a result, behave differently ( cm. Band theory of conductivity of solids and Theory of molecular orbitals). Thus, the freedom of valence electrons to move inside a substance is determined by its molecular crystal structure. On the whole, according to the electrically conductive properties, all substances can (with some degree of convention) be subdivided into three categories, each of which has pronounced characteristics of the behavior of valence electrons under the influence of an external electric field.
Conductors
In some substances, valence electrons move freely between atoms. First of all, this category includes metals in which the electrons of the outer shells are literally in the "common property" of the atoms of the crystal lattice ( cm. Chemical Bonds and Electronic Theory of Conduction). If you apply an electric voltage to such a substance (for example, connect the poles of a storage battery to its two ends), the electrons will begin an unobstructed, orderly movement in the direction of the south pole potential difference, thereby creating an electric current. Conductive substances of this kind are usually called guides. The most common conductors in technology are, of course, metals, primarily copper and aluminum, which have a minimum electrical resistance and are quite widespread in earthly nature. It is from them that high-voltage electrical cables and household electrical wiring are mainly made. There are other types of materials with good electrical conductivity, such as saline, alkaline and acid solutions, as well as plasma and some types of long organic molecules.
In this regard, it is important to remember that electrical conductivity can be due to the presence in a substance not only of free electrons, but also of free positively and negatively charged ions of chemical compounds. In particular, even in ordinary tap water, so many different salts are dissolved, which decompose when dissolved into negatively charged cations and positively charged anions that water (even fresh) is a very good conductor, and this should not be forgotten when working with electrical equipment in conditions of high humidity - otherwise you can get a very noticeable electric shock.
Insulators
In many other substances (in particular, glass, porcelain, plastics), electrons are firmly attached to atoms or molecules and are not capable of free movement under the influence of an external electric voltage. Such materials are called insulators.
Most often in modern technology, various plastics are used as electrical insulators. In fact, any plastic consists of polymer molecules- that is, very long chains of organic (hydrogen-carbon) compounds - which, moreover, form complex and very strong interweaving. The easiest way to imagine polymer structures is to imagine a plate of tangled and stuck together long and thin noodles. In such materials, electrons are firmly attached to their ultra-long molecules and are unable to leave them under the influence of external stress. They have good insulating properties and amorphous substances such as glass, porcelain or rubber that do not have a rigid crystalline structure. They are also often used as electrical insulators.
Both conductors and insulators play an important role in our technogenic civilization, which uses electricity as the main means of transmitting energy over a distance. Electricity travels along conductors from power plants to our homes and to all kinds of industrial enterprises, and insulators ensure our safety, protecting us from the destructive consequences of direct contact of the human body with high electrical voltage.
Semiconductors
Finally, there is a small category of chemical elements that occupy an intermediate position between metals and insulators (the most famous of them are silicon and germanium). In the crystal lattices of these substances, all valence electrons, at first glance, are bound by chemical bonds, and it would seem that there should not be any free electrons to ensure electrical conductivity. However, in reality, the situation looks somewhat different, since some of the electrons are knocked out of their outer orbits as a result of thermal motion due to insufficient energy of their binding with atoms. As a result, at temperatures above absolute zero, they still have a certain electrical conductivity under the influence of external voltage. Their conductivity coefficient is rather low (the same silicon conducts an electric current millions of times worse than copper), but they still conduct some kind of current, albeit insignificant. Such substances are called semiconductors.
As it turned out as a result of research, electrical conductivity in semiconductors, however, is due not only to the movement of free electrons (the so-called n-conduction due to the directed motion of negatively charged particles). There is also a second mechanism of electrical conductivity, which is quite unusual. When an electron is released from the crystal lattice of a semiconductor due to thermal motion, a so-called hole- a positively charged cell of the crystal structure, which can at any moment be occupied by a negatively charged electron that has jumped into it from the outer orbit of a neighboring atom, where, in turn, a new positively charged hole is formed. Such a process can continue for an arbitrarily long time - and it will look from the outside (on a macroscopic scale) that the electric current under external voltage is not due to the movement of electrons (which just jump from the outer orbit of one atom to the outer orbit of a neighboring atom), but directed migration of a positively charged hole (electron deficit) towards the negative pole of the applied potential difference. As a result, the second type of conductivity is also observed in semiconductors (the so-called hole or p-conductivity), due, of course, also to the motion of negatively charged electrons, but from the point of view of the macroscopic properties of matter, which is represented by a directed current of positively charged holes towards the negative pole.
The hole conduction phenomenon is most easily illustrated with the example of a traffic jam. As the car stuck in it moves forward, free space is formed in its place, which is immediately occupied by the next car, the place of which is immediately taken by the third car, etc. This process can be imagined in two ways: you can describe the rare the numbers of people in a long traffic jam; it is easier, however, to characterize the situation in terms of episodic movement in the opposite direction of a few voids between cars stuck in traffic. It is guided by a similar analogy that physicists talk about hole conduction, conditionally taking for granted that an electric current is conducted not due to the movement of numerous negatively charged electrons that rarely move from their place, but due to the movement in the opposite direction of positively charged voids in the outer orbits of semiconductor atoms, which they agreed to call "holes". Thus, the dualism of electron-hole conduction is purely arbitrary, since from a physical point of view, the current in semiconductors, in any case, is due exclusively to the directional motion of electrons.
Semiconductors have found wide practical application in modern radio electronics and computer technologies precisely because their conductive properties are easily and accurately controlled by changing external conditions.
PART A. Multiple Choice Tests
1. Distribution of electrons by energy levels in a lithium atom:
2. The number of electrons on the outer electron layer of alkali metal atoms:
3. The type of chemical bond in a simple sodium substance:
4. A simple substance with the most pronounced metallic properties:
5. The radius of the atoms of the elements of the main subgroup with an increase in the nuclear charge:
6. The calcium atom differs from the calcium ion:
7. Reacts most vigorously with water:
8.Does not interact with hydrochloric acid:
9. Aluminum hydroxide interacts with a substance, the formula of which is:
10. A row in which all substances react with iron:
PART B. Tasks with a free answer
11. Suggest three ways to obtain calcium hydroxide. Confirm the answer with the reaction equations.
12. Determine the substances X, Y, Z, write down their chemical formulas.
13. How, using any reagents (substances) and lithium, to get oxide, base, salt? Write the reaction equations in molecular form.
14. Arrange the metals: aluminum, lead, gold, copper in order of increasing relative conductivity (Fig. 2).
Option 1.
1. Distribution of electrons by energy levels in the magnesium atom:
G. 2e, 8e, 2e.
A.1.
3. The type of chemical bond in a simple substance of lithium:
G. Metallic.
G. Strontium.
5. The radius of the atoms of the elements of the 3rd period with an increase in the charge of the nucleus from an alkali metal to a halogen:
G. Decreases.
6. The aluminum atom differs from the aluminum ion:
B. The radius of the particle.
A. Potassium.
eight . Does not interact with dilute sulfuric acid:
V. Platina.
9. Beryllium hydroxide interacts with a substance, the formula of which is:
A. KON (solution).
10. A row in which all substances react with zinc:
A. HCl, NaOH, H2SO4.
11. Suggest three ways to get potassium hydroxide. Confirm the answer with the reaction equations.
2K + 2H2O = 2KON + H2
K2O + H2O = 2KON
K2CO3 + Ca (OH) 2 = CaCO3 ↓ + 2KON
X CuO
Y CuSO4
Z Cu (OH) 2
13. How, using any reagents (substances) and barium, to get oxide, base, salt? Write the reaction equations in molecular form.
13.2Ba + O2 = 2BaO
Ba + 2H2O = Ba (OH) 2 + H2
Ba + Cl2 = BaCl2
14. Arrange metals: iron, tin, tungsten, lead in order of increasing relative hardness (fig. 1).
lead - tin - iron - tungsten
15. Calculate the mass of metal that can be obtained from 144 g of iron oxide (II).
n (FeO) = 144g / 72g / mol = 2 mol
n (Fe) = 2 mol
m (Fe) = 2mol * 56g / mol = 112g
Option 2.
PART A. Multiple Choice Tests
1. Distribution of electrons by energy levels in a lithium atom:
B. 2e, 1f.
2. The number of electrons on the outer electron layer of alkali metal atoms:
A. 1.
3. The type of chemical bond in a simple sodium substance:
G. Metallic.
4. A simple substance with the most pronounced metallic properties:
G. Indium.
B. Increases.
6. The calcium atom differs from the calcium ion:
B. The number of electrons in the external energy level.
7. Reacts most vigorously with water:
A. Barium.
B. Silver.
9. Aluminum hydroxide interacts with a substance, the formula of which is:
B. NaOH (p-p).
10. A row in which all substances react with iron:
B. Cl2, CuC12, HC1.
PART B. Tasks with a free answer
11. Suggest three ways to obtain calcium hydroxide. Confirm the answer with the reaction equations.
Ca + 2H2O = Ca (OH) 2 + H2
CaO + H2O = Ca (OH) 2
CaCl2 + 2KOH = Ca (OH) 2 + 2KCl
12. Determine the substances X, Y, Z, write down their chemical formulas.
X ZnO
Y ZnCl2
Z Zn (OH) 2
13. How, using any reagents (substances) and lithium, to get oxide, base, salt? Write the reaction equations in molecular form.
4Li + O2 = 2Li2O
2Li + 2H2O = 2LiOH + H2
2Li + Cl2 = 2LiCl
14. Arrange the metals: aluminum, lead, gold, copper in order of increasing relative conductivity (Fig. 2).
Lead, aluminum, gold, copper.
15. Calculate the mass of metal that can be obtained from 80 g of iron (III) oxide.
n (Fe2O3) = 80g / 160g / mol = 0.5 mol
n (Fe) = 2n (Fe2O3) = 1 mol
m (Fe) = 1 mol * 56g / mol = 56g
Option 3.
PART A. Multiple Choice Tests
1. Distribution of electrons by energy levels in the sodium atom:
B. 2e, 8e, 1e.
2. The number of the period in the Periodic Table of D. I. Mendeleev, in which there are no chemical elements-metals:
A. 1.
3. The type of chemical bond in a simple calcium substance:
G. Metallic.
4. A simple substance with the most pronounced metallic properties:
G. Natrii.
5. The radius of the atoms of the elements of the 2nd period with an increase in the charge of the nucleus from an alkali metal to a halogen:
G. Decreases.
6. The magnesium atom differs from the magnesium ion:
B. Particle charge.
7. Reacts most vigorously with water:
G. Rubidium.
8.Does not interact with dilute sulfuric acid:
G. Mercury.
9. Beryllium hydroxide does not interact with a substance, the formula of which is:
B. NaCl (solution)
10. A row in which all substances react with calcium:
B. C12, H2O, H2SO4.
PART B. Tasks with a free answer
11. Suggest three ways to obtain iron sulfate (III). Confirm the answer with the reaction equations.
Fe + H2SO4 = FeSO4 + H2
FeO + H2SO4 = FeSO4 + H2O
Fe + CuSO4 = FeSO4 + Cu
12. Determine the substances X, Y, Z, write down their chemical formulas.
X Fe2O3
Y FeCl3
Z Fe (OH) 3
13. How, using any reagents (substances) and aluminum, to obtain an oxide, amphoteric hydroxide? Write the reaction equations in molecular form.
4Al + 3O2 = 2Al2O3
2Al + 6H2O = 2Al (OH) 3 + 3H2
14. Arrange the metals: copper, gold, aluminum, lead in order of increasing density (fig. 3).
aluminum, copper, lead, gold
15. Calculate the mass of the metal obtained from 160 g of copper oxide (II).
n (CuO) = 160g / 80g / mol = 2mol
n (Cu) = n (CuO) = 2 mol
m (Cu) = 2 mol * 64g / mol = 128g
Option 4.
PART A. Multiple Choice Tests
1. Distribution of electrons by energy levels in the aluminum atom:
B. 2f, 8f, 3f.
2. The number of a group in the Periodic Table of D. I. Mendeleev, consisting only of chemical elements-metals:
B. II.
3. The type of chemical bond in a simple substance magnesium:
G. Metallic.
4. A simple substance with the most pronounced metallic properties:
G. Rubidium.
5. The radius of the atoms of the elements of the main subgroup with an increase in the nuclear charge:
B. Increases.
6. The sodium atom and ion are different:
B. The radius of the particle.
7. Reacts most vigorously with water:
B. Potassium.
8.Does not interact with hydrochloric acid:
B. Copper.
9. Aluminum hydroxide does not interact with a substance, the formula of which is:
B. KNO3 (p-p).
10. The row in which all substances react with magnesium:
B. C12, O2, HC1.
PART B. Tasks with a free answer
11. Suggest three ways to obtain aluminum oxide. Confirm the answer with the reaction equations.
2Al (OH) 3 = Al2O3 + 3H2O
4Al + 3O2 = 2Al2O3
2Al + Cr2O3 = Al2O3 + 2Cr
12. Determine the substances X, Y, Z, write down their chemical formulas.
X CaO
Y Ca (OH) 2
Z CaCO3
13. How, using any reagents (substances), to get oxide, base, salt from zinc? Write the reaction equations in molecular form.
2Zn + O2 = 2ZnO
Zn + 2H2O = Zn (OH) 2 + H2
Zn + Cl2 = ZnCl2
14. Arrange metals: aluminum, tungsten, tin, mercury in decreasing order of melting point (fig. 4).
tungsten, aluminum, tin, mercury
15. Calculate the mass of metal that can be obtained by aluminothermy from 34 g of chromium oxide (II).
n (CrO) = 34g / 68g / mol = 0.5 mol
n (Cr) = n (CrO) = 0.5 mol
m (Cr) = 0.5 mol * 52g / mol = 26g
PART 1
1. Metals (M) are located in groups I-III, or in the lower part of groups IV-VI. Only metals are in the B group.
2. Metal atoms have 1-3 electrons in the outer electron layer and a relatively large radius of the atom. Metal atoms tend to donate external electrons.
3. Simple substances- metals consist of elements linked by a metallic chemical bond, which can be displayed by the general scheme:
4. All M - solids except for Hg. The softest metals of the IA group, the hardest — Cr.
5.M have thermal and electrical conductivity and have a metallic luster.
6. Tin has the property of forming two simple substances- white and gray, that is, by the property of allotropy.
7. Complete the table "Properties and uses of some metals".
PART 2
1. Select the names of simple substances - metals. From the letters corresponding to the correct answers, you will compose the name of the metal, which in Greek means "stone": lithium.
2) magnesium L
3) calcium AND
5) copper T
7) gold and
8) mercury Y
2. The following statements about metals are incorrect:
5) non-plastic and non-forging
3. Select the four most electrically conductive metals (place the numbers in descending order of conductivity) from the list:
1) silver
2) gold
3) aluminum
4) iron
5) manganese
6) potassium
7) sodium
Answer: 1, 2, 3, 7.
4. Make schemes for the formation of a metallic chemical bond for substances with the formulas:
5. Analyze the picture "Metal crystal lattice".
Make a conclusion about the reasons for the plasticity, thermal and electrical conductivity of metals.
Each metal atom is surrounded by eight neighboring atoms. The detached outer electrons freely move from one formed ion to another, connecting the ionic core of the metal into a giant molecule. High thermal conductivity, electrical conductivity of metals are due to the presence in their crystal lattices of mobile electrons moving under the action of an electric field. Most metals are plastic due to the displacement of layers of metal atoms without breaking the bond between them.
6. Fill in the "Metals" table. Find the data for the table using additional sources of information, including the Internet.
7. Using the Internet and other sources of information, prepare a short message on the topic "Mercury in Human Life" according to the following plan:
1) knowledge about mercury in antiquity and the Middle Ages;
2) toxicity of mercury and safety measures when working with it;
3) the use of mercury in modern industry.
1) Mercury was one of the 7 metals, it is considered the progenitor of all metals, they used not only mercury itself, but also its alloy, cinnabar.
2) It is very toxic, it evaporates at room temperature and, if inhaled, can be toxic to humans. Accumulating in the body, it affects the internal organs, respiratory tract, hematopoietic organs and the brain.
3) Mercury is widely used. In the chemical industry as a cathode in the production of sodium hydroxide, as a catalyst in the production of many organic compounds, in the dissolution of uranium blocks (in nuclear power). This element is used in the manufacture of fluorescent lamps, quartz lamps, pressure gauges, thermometers and other scientific instruments.
