chemistry lesson

An atom is a complex particle

The purpose of the lesson: to summarize information about the most important discoveries of physics of the XIX —XX centuries., proving the complexity of the structure of atoms of chemical elements; to teach to explain the structure of the atom, based on some models of classical theory; to consolidate knowledge of modern ideas about the structure of the atom based on quantum mechanics.

Basic concepts: macro-world, micro-world, quantum mechanics, nucleons (protons, neutrons), nuclides, isotopes, particle-wave dualism of micro-world particles, chemical element.

Equipment: Mendeleev PSCE, tables "Structure of the atom".

Lesson progress

I. Organizational moment

Inform students of the results of the test of the previous lesson, on the basis of which to set the students the main goals and objectives of studying the topic "Structure of the atom", familiarize them with the nodal issues of the topic, types of control of acquired knowledge, skills

II. Learning new material

Plan of presentation

1. the most Important discoveries of physics of the late XIX—early XX century.

2. Models of the classical theory of atomic structure, explanation of their failure.

3. Modern ideas about the structure of the atom based on quantum mechanics. Proton-neutron theory.

4. Nuclides are different forks of atoms. Isotopes. Hydrogen isotope.

5. Forms of existence of a chemical element.

It is desirable to read the first point of the plan on page 3 of the textbook the concept of "atom", fundamental discoveries proving the complexity of the structure of the atom, followed by a note in the workbook.

In 1904, J. Thomson proposed a model of the atom called "plum pudding". The atom as a whole is electroneutral, since it is like a spherical pudding drop with a positive charge, inside the sphere of which negatively charged slithinelectrons are embedded. performing oscillatory movements, through which the atom emits electromagnetic energy. However, this model has not been experimentally confirmed and remains a hypothesis.

In 1911, E. Rutherford proposed a planetary model of the atom. Like the movement of planets in closed orbits around the Sun, the atom model is a positively charged nucleus and electrons rotating around the nucleus in closed stationary orbits. However, this model could not explain the phenomena of radiation and absorption of energy by the atom. E. Rutherford is considered the founder of the modern theory of the atom, and we still use his theoretical model of the structure of the atom.

In 1900, M. Planck, in 1905, A. Einstein and N. Bohr introduced theoretical ideas and quantum representations to the Rutherford planetary model — postulates (a postulate is a statement accepted without proof).

The first postulate: an electron can not rotate around the nucleus in any, but only in some specific circular orbits. These orbits are called stationaryorbits . In this case, the energy of the atom is neither absorbed nor radiated.

The second postulate: radiation or absorption of energy by an atom occurs when an electron jumps from one stationary orbit to another. In this case, a separate portion of energy — a quantum-is emitted or absorbed.

N. Bohr introduced quantum concepts about the structure of the atom, but he used traditional classical concepts of mechanics, considering the electron as a particle moving at strictly defined speeds along strictly defined trajectories. His theory was an important step in the development of ideas about the structure of the atom.

The hypothesis proposed by M. Planck and A. Einstein about light quanta (photons) shows that it is impossible to automatically extend the laws of nature, which are valid for most bodies-objects of the macrocosm, to negligibly small objects-of the microcosm (atoms, electrons, etc.)

In the 20s of the XX century, after the emergence and development of a new branch of theoretical physics — quantum or wave mechanics — the problem of describing the properties and behavior of particles in the microcosm was solved. This theory characterizes particles of the microcosm as objects with a dual nature-particle-wave dualism: they are simultaneously particles (corpuscles) and waves. The wave-particle dualism of micro-world objects is also confirmed experimentally by the interference and diffraction of electrons familiar from the physics course. Interference — the superimposition of waves on each other. Diffraction — огибаниеthe wave's circumference around an obstacle. This proves that the v electron has wave properties. Blackening of the photolayer only in one place indicates the presence of its corpuscular properties. If the electron were only a wave, it would more or less evenly illuminate the photographic plate (Fig. 1 p. 5 of the textbook).

In 1932, the proton-neutron theory of the nucleus was developed, according to which the nuclei of atoms consist of protons having a charge of +1 and mass of 1, and neutrons having a charge of 0 and mass of 1. They are called nucleons.

An atom is an electroneutral system of interacting elementary particles consisting of a nucleus (formed by protons and neutrons) and electrons.

The ordinal number of an element in D. I. Mendeleev's PSE corresponds to the charge of the nucleus of an atom, i.e. it indicates the number of protons in it. The number of neutrons is determined by the formula N-A-Z, where A is the mass number and Z is the ordinal number of the element. The number of electrons in an atom corresponds to the ordinal number of the element in the PSE.

Example: The element's sequential number is 25. the Mass number is 55. What is the composition of its atom?

Answer: The charge of the nucleus of an atom is +25; in the nucleus of an atom there are 25 protons, neutrons 55-25 = 30; in the atom there are 25 electrons.

Question: What should we expect if the number of protons and neutrons in an atom changes?

Answer: Changing the number of protons in an atom leads to the formation of a new chemical element because the charge of the atom's nucleus changes.

Changing the number of neutrons in an atom leads to a change in the atomic mass of the element, the charge of the nucleus of the atom does not change. Isotopes are formed-varieties of atoms of the same element, having the same charge of the nucleus, but different relative atomic mass.

Example: Isotopes of chlorine: ₊₁₇SL, at. weight 35, and₊₁₇CC, at. mass 37; potassium isotopes₊₁₉K, at. weight 39, and₊₁₉K, at. weight 40.

The properties of isotopes of the same element are the same, because they have the same nuclear charge, although their relative atomic mass is different, because they contain a different number of neutrons; the change in the atomic mass of the elements is insignificant — it has a fractional value.

The isotopes of hydrogen have their own names and chemical symbols:

Protium-N-has a nuclear charge of +1 and a mass of atom 1, there are no neutrons in the nucleus.

Deuterium-D-has the charge of the nucleus of the atom +1 and the mass of the atom 2, the neutrons in the nucleus-I.

Tritium-T has the charge of the nucleus of an atom +1 and the mass of an atom 3, neutrons in the nucleus-2.

Question: Why do hydrogen isotopes differ significantly in their properties?

Answer: The isotopes of hydrogen have mass change is highly significant in a multiple of the value of time.

On the basis of the above, we should give a modern interpretation of the chemical element.

A chemical element is a collection of atoms with the same charge of the nucleus, i.e., with the same number of protons in it.

The following forms are known (methods) existence of a chemical element: free atoms, simple substances, complex substances.

Example: Hydrogen can exist in the form of free atoms, in the form of diatomic molecules, and also be part of the molecules of a complex substance.

Then the teacher together with the students makes a summary table.

Relationship of content and form on the example of three forms of existence of a chemical element

Conclusion: content and form взаимосвязаныare interrelated. The determining role is given to the content (the charge of the atomic nucleus, the composition of simple and complex substances), but the form is not passive, it affects the content (isotopes , allotropes, isomers).

III. Anchoring on key issues of the topic

Working with questions № 1, 2, 3, 4 § 1.

Students read out the question in the paragraph and write the answer to it according to the summary in the workbook or according to the text of the textbook.

IV. Homework assignment

I) § 2: 2) determine the composition of atoms № 13, № 56, № 30, № 101: 3) answer the question, what are the similarities and differences of argon atoms with masses of 39 and 40?