Physical properties of metals presentation for a chemistry lesson on the topic

Position of non-metals and metals: periodic table

It is not always possible to find out which group a chemical element belongs to by external signs and physical properties. The properties of metals and nonmetals can be determined by their position on the periodic table.

To do this, you need to visually draw a diagonal from boron to astatine, from 5 to 85 numbers. In the upper right corner there will be predominantly non-metals. There are a minority of them in the table, only 22 elements. Metals are found on the right side of the periodic table at the top—mostly in groups I, II, and III.

Lesson summary - Metals - 9th grade

Communicative skills: be able to express your thoughts in written and oral form, lead a discussion, be able to prove your point of view.

Regulatory:

be able to independently discover and formulate an educational problem, determine a goal, and draw up a plan for solving problems.

The lesson took into account the focus of the class. There are 12 people in the class: 3 boys and 8 girls. The class has average creative potential. The main activity is study, but not all students are interested in acquiring new knowledge. Class performance is average. Students are active, love to prove their positions, have sufficient knowledge and skills, are motivated to self-education, are ready to show a creative approach to business, and look for non-standard ways to solve problems.

The general level of discipline in the class is acceptable. Therefore, the motivational stage went according to my plans. The children became interested.

Each student feels comfortable in the classroom. There were no conflict situations between students in the group. Since not all students in the class are interested in acquiring new knowledge, I set myself the following tasks:

— to interest students using a demonstration of additional sources (samples of metals and alloys and products made from them) and electronic presentation;

- arouse interest in the use of metals and alloys in everyday life;

— application of the research method (studying the properties of metals).

To solve the problems, I used the following didactic materials:

— samples of metals and alloys and products made from them;

— multimedia complex (computer, projector);

— multimedia presentation;

- textbook by O. S. Gabrielyan “Chemistry. 9th grade";

- additional literature.

The study of new material was carried out in accordance with the requirements of the Federal State Educational Standard: it began with leading questions showing its connection with previously covered material, leading students to independently formulate a new topic, determine the purpose of the lesson, and draw up a lesson plan. When determining the topic, the emphasis was placed on the students’ existing knowledge and skills, special attention was paid to the practical significance of the knowledge acquired, so the students were able to name the topic of the lesson.

In this lesson, a systemic activity-based teaching method was used, which was implemented in the educational and practical activities of students.

The research method of teaching is the most effective way to obtain and master material for teenagers, therefore it aims them at practice-oriented activities. The use of a practical task helped students understand how to apply the knowledge acquired in the lesson in everyday life, as well as compliance with safety precautions.

Energy level

The differences between nonmetals and metals are primarily due to the structure of their atoms. Let's start with the number of electrons in the outer energy level. For metal atoms it varies from one to three. As a rule, they have a large radius, so metal atoms easily give up their outer electrons, since they have strong reducing properties.

Nonmetals have a larger number of electrons in the outer level. This explains their oxidative activity. Nonmetals add missing electrons, completely filling the energy level. The strongest oxidizing properties are exhibited by non-metals of the second and third periods of groups VI-VII.

A filled energy level contains 8 electrons. The halogens with valence I have the greatest oxidizing ability. Fluorine is the leader among them, since this element has no free orbitals.

2.2. General chemical properties of nonmetals.

With hydrogen, nonmetals form volatile compounds, such as hydrogen fluoride HF, hydrogen sulfide H3S, ammonia NH4, methane CH5. When dissolved in water, hydrogen compounds of halogens, sulfur, selenium and tellurium form acids of the same formula as the hydrogen compounds themselves: HF, HCl, HCl, HBr, HI, H3S, H3Se, H3Te.

With oxygen, nonmetals form acidic oxides. In some oxides they exhibit a maximum oxidation state equal to the group number (for example, SO2, N2O5), while in others it is lower (for example, SO2, N2O3).

Structure of metals and non-metals: crystal lattices

The physical properties of substances are determined by the arrangement of elementary particles. If you conditionally connect them with imaginary lines, you get a structure called a crystal lattice. Its nodes can contain different structures: atoms, molecules or charged particles - ions.

Some nonmetals form an atomic crystal lattice, the particles of which are connected by covalent bonds. Substances with this structure are solid and non-volatile. For example, phosphorus, silicon and graphite.

In a molecular crystal lattice, the connection between elementary particles is weaker. Typically, such nonmetals are in a liquid or gaseous aggregate state, but in some cases they are solid, fusible nonmetals.

In any metal sample, some of the atoms lose outer electrons. At the same time, they turn into positively charged particles - cations. The latter combine again with electrons, forming neutrally charged particles - cations, electrons and atoms are simultaneously located in the metal lattice.

Test on the topic

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   How do metallic properties change in the periodic table?

   Start test

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Physical properties

Let's start with the state of aggregation. It is traditionally believed that all metals are solids. The only exception is mercury, a viscous silvery liquid. Its vapors are a contaminant - a toxic substance that causes poisoning of the body.

Another characteristic feature is a metallic luster, which is explained by the fact that the metal surface reflects light rays. Another important feature is electrical and thermal conductivity. This property is due to the presence of free electrons in metal lattices, which begin to move directionally in an electric field. Mercury conducts heat and current best of all, silver has the lowest performance.

The metal bond determines malleability and ductility. According to these indicators, gold is the leader, from which you can roll out a sheet as thick as a human hair.

Most often, the physical properties of metals and non-metals are opposite. Thus, the latter are characterized by low electrical and thermal conductivity and lack of metallic luster. Under normal conditions, nonmetals are in a gaseous or liquid state, while solids are always brittle and fusible, which is explained by the molecular structure of nonmetals. Diamond, red phosphorus and silicon are refractory and non-volatile; they are substances with a non-molecular structure.

Structure and properties of metals

3. STRUCTURE AND PROPERTIES OF METALS

3.1. General characteristics of metals.

In technology, metals are understood as materials that have a whole range of specific physical, chemical, technological and mechanical properties.

Physical properties reflect the behavior of materials in various fields (gravitational, thermal, electromagnetic). The most characteristic physical properties of metals include their relatively high density, thermal and electrical conductivity

, as well as
a metallic luster
and the ability to emit electrons when heated.

From the point of view of chemical properties, metals are chemical elements located on the left side of the periodic table. The atoms of these elements have a small number of electrons in their outer electron shell that are weakly bound to the nucleus. When entering into a chemical interaction with nonmetals, metal atoms easily give them their outer valence electrons and become positively charged ions.

Technological properties reflect the ability of materials to be subjected to one or another type of processing. The most characteristic technological properties of metals include their relatively good deformability

(in particular,
stampability, malleability
),
weldability
, as well as the ability to obtain products from them by casting.

Mechanical properties reflect the ability of materials to resist deformation and destruction under the influence of various types of loads. The most characteristic mechanical properties of metals include their fairly high ductility and toughness.

, as well as relatively high strength and hardness.

Most of the above-mentioned characteristic properties of metals are explained by the peculiarities of their structure. Atoms of metals in a solid state are connected to each other by a specific chemical bond called a metallic bond.

. This bond occurs due to the sharing of all valence electrons by metal atoms. In this case, the atoms themselves become positively charged ions, and the electrons shared by them form a “gas”, or more precisely a “liquid”, in the volume of the metal, relatively free electrons. Thus, at the atomic level, metals look like a collection of positively charged ions located at the nodes of a crystal lattice, which are “washed by an electron liquid.”

The presence of electronic liquid (gas) explains such characteristic properties of metals as their high electrical and thermal conductivity, as well as metallic luster. In addition, the metallic bond allows atomic layers to slide relatively easily relative to each other during plastic deformation, which provides metals with fairly high plasticity.

3.2. Classification of metals.

All metals can be divided into two large groups: ferrous metals and non-ferrous metals.

Ferrous metals have a dark gray color, a high melting point and relatively high hardness. Non-ferrous metals have a characteristic color (white, yellow, red), have greater ductility, less hardness and a relatively low melting point.

Ferrous metals, in turn, can be divided into 5 groups:

1. Metals of the iron group - Fe, Co, Ni and Mn.

Fe forms the basis of the most common alloys in industry - steels and cast irons. The remaining metals in this group are used either as additives in iron alloys, or as a base for the corresponding alloys (cobalt, nickel, etc.).

2. Refractory metals - Ti, V, Cr, Mo, W, etc.

Their melting point is higher than that of iron. Metals of this group are usually used as additives to alloy steels, or as a basis for special alloys (for example, titanium). Tungsten in its pure form is used to make filaments in electric lamps.

3. Uranium metals - actinides - Ac, Th, etc. They are used, as a rule, in alloys for nuclear energy.

4. Rare earth metals - lanthanides - La, Ce, etc. Usually found in mixed form and have similar properties. They are usually used in special alloys with special properties.

5. Alkali metals - Li, Na, K, etc. They are highly active and therefore are not used in free form.

Non-ferrous metals are divided into 3 groups:

1. Light metals - Al, Mg, Be. They have a relatively low density. Due to its high electrical conductivity, Al is widely used for the manufacture of electrical wires.

2. Noble metals - Au, Ag, Pt, etc. including Cu. They are characterized by high corrosion resistance, ductility and electrical conductivity. Widely used in microelectronics and jewelry. Copper is also used to produce bronzes and brasses.

3. Low-melting metals - Sn, Pb, Zn, Hg, etc. They have a relatively low melting point. The melting point of mercury (Hg) is below room temperature and therefore this metal is liquid under normal conditions.

The most common metal on the globe is Al (8.8%). In second place is iron (4.65%).

3.3. Crystal structure of metals.

Unlike a covalent bond, a metal bond is not strictly directed in space and allows an arbitrary number of interacting particles. As a result, metal atoms, tending to the state with the lowest energy, are most compactly located in space. Such dense atomic packings correspond to 3 types of crystal structures: body-centered cubic structure (bcc structure), face-centered cubic structure (fcc structure) and hexagonal close-packed structure (hcp structure). These structures are most often observed in metals.

1. The bcc structure (Fig. 3.2.) is observed in such metals as Cr, Mo, W, V, etc. The coordination number in this case is 8 (there are 8 similar atoms at the nearest equal distance from any atom). The compactness coefficient reaches a value of 0.68. This means that 68% of the metal's volume is occupied by atoms, and the rest is voids. The basis is formed by two metal atoms (one atom located in the center of the bcc cell belongs completely to it, and another atom (8 by ⅛) is provided by nodes located at the vertices of the cell).

Rice. 3.2. Unit cell Fig. 3.3. Unit cell

BCC structures. fcc structures.

2. The fcc structure (Fig. 3.3) is characteristic of Al, Cu, Ni, Ag, Au and Pt. The coordination number here is 12, and the compactness coefficient is 0.74. The basis is formed by four metal atoms (each atom located in the center of the face belongs to the cell only half, and since there are 6 such atoms, the result is exactly 3; plus one atom is provided by the nodes located at the vertices of the cell).

3. The hcp structure is observed in metals such as Mg, Zn, Be, etc. Although the hcp structure can be described using a smaller primitive cell, in this case it is better to choose a hexagonal prism as a unit cell, which more clearly reflects the hexagonal symmetry crystal (Fig. 3.4).

Rice. 3.4. Unit cell of the hcp structure.

The coordination number for such a structure is 12 (if we take the atom located in the center of the face as the reference point, then there are 6 atoms at an equal closest distance from it, plus 3 atoms above and below). The compactness coefficient, like that of the fcc structure, has a value of 0.74. The basis is formed by 6 metal atoms (3 atoms inside the prism belong completely to it; the atoms in the center of the upper and lower faces belong to the cell only half, and each of the 12 atoms at the vertices of the prism belongs to the cell in question only 1/6 part, since it is located at the intersection of 6 similar cells).

Other, less dense structures are also found in metals, but much less frequently than the three mentioned above.

3.4. Polymorphism of metals.

Polymorphism

This is a phenomenon when a material in one temperature or pressure range has one crystalline structure, and in another - another.
The temperature and pressure at which a change in the crystal structure of a material is observed is called the temperature and pressure of polymorphic (allotropic) transformation
.

Various crystallographic modifications of one material are usually denoted by the letters of the Greek alphabet α, β, g, δ, ε, σ, etc. The modification observed at the lowest temperatures is denoted by the letter α, at higher temperatures - β, etc.

A striking example of polymorphism in non-metallic materials is the presence of two crystallographic modifications of pure carbon, which we know as diamond and graphite. Both materials are identical in chemical composition, and the difference is only in the crystal structure. As a result, the properties of these materials are significantly different. Graphite is soft, brittle and opaque, while diamond is one of the hardest minerals found in nature and is generally transparent.

Polymorphism is a fairly common phenomenon in the world of metals. For example, with increasing temperature, the hcp structure of Co transforms into an fcc structure, and for Ti, the hcp structure transforms into a bcc structure.

Polymorphism is most pronounced in iron, which changes its crystal structure twice when heated.

bcc fcc bcc liquid

α-Fe β-Fe γ-Fe δ-Fe

768 911 1392 1539 T, °C.

At temperatures below 768°C, iron is ferromagnetic, and at temperatures above 768°C it is paramagnetic. Previously, it was believed that this was due to a change in the crystal structure of iron and therefore ferromagnetic iron began to be designated α-Fe, and paramagnetic iron as β-Fe. Later it turned out that the change in the magnetic properties of iron is not associated with a change in its crystal structure. Both irons have the same bcc structure. However, the historical division of iron into α-Fe and β-Fe was retained.

In the temperature range from 911 to 1392 °C, iron has an fcc structure and such iron is designated γ-Fe. The fcc structure differs from the bcc structure in its higher density. Therefore, when iron is heated to temperatures above 911°C, a decrease in the size (volume) of the sample is observed.

In the temperature range from 1392 to 1539°C, iron again has a bcc structure, but with a lattice parameter slightly larger than that of α-Fe. Such iron is designated δ-Fe. At a temperature of 1539°C, pure iron melts and turns into liquid.

Another striking example of metal polymorphism is the so-called “tin plague”. At temperatures below -30°C, the white and ductile β-tin (β –Sn) turns into α-Sn, which is a gray powder.

What are semimetals

In the periodic table, between metals and non-metals, there are a number of chemical elements that occupy an intermediate position. They are called semimetals. Semimetal atoms are linked by covalent chemical bonds.

These substances combine the characteristics of metals and non-metals. For example, antimony is a silvery-white crystalline substance that reacts with acids to form salts—typical metallic properties. On the other hand, antimony is a very fragile substance that cannot be forged, and it can even be crushed by hand.

So, typical non-metals and metals have opposite properties, but this division is quite arbitrary, since a number of substances combine both characteristics.

Chemical

Metals are strong reducing agents. Elements to the left of hydrogen react with simple and complex substances, forming salts, acids, oxides and hydroxides:

• with oxygen –
  4Al + 3O2 → 2Al2O3;
• with halogens –
  2K + Cl2 → 2KCl;
• with sulfur –
  Fe + S → FeS;
• with phosphorus –
  3Mg + 2P → Mg3P2;
• with nitrogen –
  3Ca + N2 → Ca3N2;
• with acids –
  Zn + 2HCl → ZnCl2 + H2;
• with salts (replaces a less active metal) –
  AgNO3 + Na → NaNO3 + Ag;
• with water –
  Ca + 2H2O → Ca(OH)2 + H2.

Along with the increase in metallic properties in the periodic table, the acid-base properties of metal oxides and hydroxides increase. From left to right, properties change from basic (sodium, potassium, calcium) to amphoteric (antimony, lead, aluminum).

How is wood similar to metal and what are their differences?

Wood is a plant material. Metal is the result of a natural chemical compound. What is the difference between wood and metal:

• Wood does not conduct electricity and ignites at a fairly low temperature compared to metals.
• Wood does not melt when exposed to high temperatures.
• Wood also conducts heat poorly, unlike metals.
• Wood is elastic, but not flexible. Metals have a lower elasticity coefficient, but they are more ductile. This way you can easily fold the wire in half without breaking it; the wood will break in half under this impact.
• Another distinguishing feature of wood from metal is that it does not corrode. There are wood species that can remain in water for a long time without rotting. Under such conditions, metals become covered with rust.
• The density of wood is quite low compared to metals. Although some metals have a density lower than wood, they are classified as light metals.

How do metals differ from each other?

Many people do not know how metals differ from metals. Their differences can be classified:

• Metals differ in color from each other, such as gold and copper.
• Metals also melt at different temperatures. Some metals, such as tin and lead, can be melted at home, but others require higher temperatures.
• Metals are divided into two groups: heavy and light. Heavy metals include those whose density is from 5 g/cm3, light metals have a density less than 5 g/cm3. Light metals include lithium, which has a density of 0.2 g/cm3; the place of the heaviest metal is shared by osmium and iridium. Their density is 22.6 g/cm3.
• Metals differ from each other in ductility and electrical conductivity. Some of them are very flexible. For example, from just 1 gram of gold you can make a thin wire of 3.5 kilometers. It will be flexible and will not break. It will not be possible to repeat this with a less ductile metal.
• Also, some metals conduct current better than others. The most electrically conductive metals are copper, silver and aluminum. They are most often used as conductive elements.