The word “atom” itself was first mentioned in the works of philosophers Ancient Greece, and translated it means “indivisible.” Without modern instruments, the philosopher Democritus, using logic and observation, came to the conclusion that any substance cannot be crushed endlessly, and in the end some indivisible smallest particle of matter must remain - an atom of matter.
And if there were no atoms, then any substance or object could be completely destroyed. Democritus became the founder of atomism - a whole doctrine that was based on the concept of the atom.
What is an atom?
An atom is the smallest electrically neutral particle of any chemical element. It consists of a positively charged core and a shell formed by negatively charged electrons. The positively charged nucleus is the core of the atom. It occupies a tiny part of the space in the center of the atom, and almost all the mass of the atom and all the positive charge are concentrated in it.
What does an atom consist of?
The nucleus of an atom is composed of elementary particles - neutrons and protons, and electrons move in closed orbitals around the atomic nucleus.
What is a neutron?
A neutron (n) is an elementary neutral particle whose relative mass is 1.00866 atomic mass unit (amu).
What is a proton?
Proton (p) represents elementary particle, the relative mass of which is 1.00728 atomic mass units, positive charge +1 and spin 1/2. Proton (translated from Greek as main, first) belongs to the baryons. In the nucleus of an atom, the number of protons is equal to the atomic number of the chemical element in Periodic table DI. Mendeleev.
What is an electron?
An electron (e–) is an elementary particle whose mass is 0.00055 amu; conditional charge of an electron: - 1. The number of electrons in an atom is equal to the charge of the nucleus of the atom (corresponds to the serial number of a chemical element in the Mendeleev Periodic System).
Around the nucleus, electrons move in strictly defined orbitals and an electron cloud is formed.
The region of space around the atomic nucleus where electrons are present with a probability of more than 90% determines the shape of the electron cloud.
Electron cloud of p-electron appearance resembles a dumbbell; Three p-orbitals can only hold a maximum of six electrons.
The electron cloud of the s electron is a sphere; at the s-energy sublevel, the maximum number of electrons that can be there is 2.
Orbitals are depicted in the form of a square, and the values of the main and secondary quantum numbers that describe this orbital are written below or above it.
This entry is called a graphical electronic formula. It looks like this:
The arrows in this formula represent an electron. The direction of the arrow corresponds to the direction of the spin - this is the electron’s own magnetic moment. Electrons that have opposite spins (in the picture these are arrows pointing in opposite directions) are called paired.
Electronic configurations of atoms of elements can be represented in the form of formulas in which:
- Indicate sublevel symbols;
- The degree of the symbol shows the number of electrons of a given sublevel;
- The coefficient in front of the sublevel symbol indicates that it belongs to this level.
Determination of the number of neutrons
To determine the number of neutrons N in the nucleus, you need to use the formula:
N=A-Z, where A is the mass number; Z is the charge of the nucleus, which is equal to the number of protons (the serial number of a chemical element in the periodic table).
As a rule, the nuclear parameters are written like this: at the top is the mass number, and to the left below the element symbol is the nuclear charge.
It looks like this:
This entry means the following:
- The mass number is 31;
- The charge of the nucleus (and, as a consequence, the number of protons) for the phosphorus atom is 15;
- The number of neutrons is 16. It is calculated as follows: 31-15=16.
The mass number roughly corresponds to the relative atomic mass of the nucleus. This is due to the fact that the masses of the neutron and proton have practically no differences.
Below we have presented part of the table, which shows the structure of the electron shells of the atoms of the first twenty elements of the Periodic Table chemical elements DI. Mendeleev. The full version is presented in our separate publication.
Chemical elements in the atoms of which the p-sublevel is filled are called p-elements. There can be from 1 to 6 electrons.
Chemical elements in the atoms of which the s-sublevel of the outer level is replenished with 1 or 2 electrons are called s-elements.
The number of electronic layers in an atom of a chemical element is equal to the period number.
Hund's rule
There is Hund's rule, according to which electrons are located in similar orbitals of the same energy level so that the total spin is the maximum possible. This means that when the energy sublevel is filled, each electron first occupies a separate cell, and only then the process of connecting them begins.
Graphic representation of the electronic formula of Nitrogen
Image of the electronic formula of Oxygen in graphical form
Graphic representation of the electronic formula of Neon
For example, in a nitrogen atom all p-electrons will occupy separate cells, and in oxygen their pairing will begin, which will be completed fully in neon.
What are isotopes
Isotopes are atoms of the same element that contain the same number of protons in their nuclei, but the number of neutrons will be different. Isotopes are known for all elements.
For this reason, the atomic masses of elements in the periodic table represent the average of the mass numbers of natural mixtures of isotopes and differ from integer values.
Is there anything smaller than the nucleus of an atom
Let's summarize. The atomic mass of natural mixtures of isotopes cannot serve the most important characteristic atom, and, as a consequence, element.
A similar characteristic of an atom will be the charge of the nucleus, which determines the structure of the electron shell and the number of electrons in it. This is interesting! Science does not stand still and scientists were able to refute the dogma that an atom is the smallest particle of chemical elements. Today the world knows quarks - they make up neutrons and protons.
Basic principles of atomic-molecular theory. Basic stoichiometric laws of chemistry. Laws of conservation of mass of matter, constancy of composition, volumetric relations, Avogadro, equivalents. Molar mass equivalent. Methods for determining atomic and molecular masses.
All substances are made up of molecules.
Molecule is the smallest particle of a substance that retains the properties of that substance. Molecules are destroyed during chemical reactions.
There are gaps between molecules: gases have the largest gaps, solids- the smallest.
Molecules move randomly and continuously.
Molecules of the same substance have the same composition and properties, molecules different substances differ from each other. friend in composition and properties.
Molecules are made up of atoms.
Atom is an electrically neutral particle consisting of a positively charged nucleus and electrons.
Chemical element- a type of atoms with the same positive nuclear charge.
Atoms of one element form molecules simple substance(02, H2, O3, Fe...). Atoms different elements form molecules complex substance(H20, Na2S04, FeClg...).
Law of conservation of mass
The mass of substances that enter into a chemical reaction is equal to the mass of substances formed as a result of the reaction.
scientist M.V. Lomonosov.
Law of Constancy of Composition
Any chemically pure compound, regardless of the method of its preparation, has a well-defined composition.
Based on this law, the composition of substances is expressed chemical formula using chemical signs and indices. For example, H 2 O, CH 4, C 2 H 5 OH, etc.
The law of constancy of composition is valid for substances molecular structure.
The composition of compounds with a molecular structure, that is, consisting of molecules, is constant regardless of the method of preparation.
Law of equivalents
Chemical elements are combined with each other in strictly defined quantities corresponding to their equivalents.
Equivalent ratio means the same number of mole equivalents. That. the law of equivalents can be formulated differently: the number of moles of equivalents for all substances participating in the reaction is the same.
Law of Multiples
Dalton's law of multiple ratios, one of the basic laws of chemistry: if two substances (simple or complex) form more than one compound with each other, then the masses of one substance per the same mass of another substance are related as whole numbers, usually small.
Law of volumetric relations
Gay-Lussac, 1808
“The volumes of gases entering into chemical reactions and the volumes of gases formed as a result of the reaction are related to each other as small whole numbers.”
Consequence. Stoichiometric coefficients in equations chemical reactions for molecules of gaseous substances show in what volume ratios gaseous substances react or are obtained.
V 1:V 2:V 3 = ν 1:ν 2:ν 3.
Periodic law and periodic system of elements by D.I. Mendeleev. Basic ideas about the structure of the atom and nucleus. Periodically changing and periodically unchanging properties of atoms and ions. Variants of the periodic table.
Periodic changes in the properties of chemical elements are caused by the correct repetition of the electronic configuration of the outer energy level (valence electrons) of their atoms with an increase in the charge of the nucleus.
Graphic representation periodic law is the periodic table. It contains 7 periods and 8 groups.
Period - horizontal rows of elements with the same maximum value of the principal quantum number of valence electrons.
The period number indicates the number energy levels in an element's atom.
Periods can consist of 2 (first), 8 (second and third), 18 (fourth and fifth) or 32 (sixth) elements, depending on the number of electrons in the outer energy level. The last, seventh period is incomplete.
All periods (except the first) begin alkali metal(s-element), and end with a noble gas (ns 2 np 6).
Metallic properties are considered as the ability of atoms of elements to easily give up electrons, and non-metallic atoms to gain electrons due to the desire of atoms to acquire a stable configuration with filled sublevels.
Groups - vertical columns of elements with the same number of valence electrons equal to the group number. There are main and secondary subgroups.
The main subgroups consist of elements of small and large periods, the valence electrons of which are located on the outer ns- and np-sublevels.
Side subgroups consist of elements of only large periods. Their valence electrons are located in the outer ns sublevel and the inner (n - 1) d sublevel (or (n - 2) f sublevel).
Depending on which sublevel (s-, p-, d- or f-) is filled with valence electrons, the elements of the periodic table are divided into:
s-elements (elements of the main subgroup of groups I and II),
p-elements (elements of the main subgroups III - VII groups),
d- elements (elements of side subgroups),
f-elements (lanthanides, actinides).
Composition of the atom.
An atom consists of an atomic nucleus and an electron shell.
The nucleus of an atom consists of protons ( p+) and neutrons ( n 0).
A number of notations are introduced to characterize atomic nuclei. The number of protons that make up the atomic nucleus is indicated by the symbol Z and call charge number or atomic number (this is serial number in Mendeleev's periodic table). The nuclear charge is Ze, Where e– elementary charge. The number of neutrons is indicated by the symbol N.
The total number of nucleons (i.e. protons and neutrons) is called mass number A:
| A = Z + N. |
The nuclei of chemical elements are designated by the symbol, where X is chemical symbol element. For example,
– hydrogen, – helium, – carbon, – oxygen, – uranium.
An isotope is a collection of atoms of the same element with the same number of neutrons in the nucleus (or a type of atom with the same number of protons and the same number of neutrons in the nucleus).
Different isotopes differ from each other in the number of neutrons in the nuclei of their atoms.
Designation of an individual atom or isotope: (E - element symbol), for example: .
Structure of the electron shell of an atom
Atomic orbital- state of an electron in an atom. The symbol for the orbital is . Each orbital has a corresponding electron cloud.
Orbitals of real atoms in the ground (unexcited) state are of four types: s, p, d And f
Orbitals of the same type are grouped into electronic (energy) sublevels:
s-sublevel (consists of one s-orbitals), symbol - .
p-sublevel (consists of three p
d-sublevel (consists of five d-orbitals), symbol - .
f-sublevel (consists of seven f-orbitals), symbol - .
The energies of orbitals of the same sublevel are the same.
When designating sublevels, the number of the layer (electronic level) is added to the sublevel symbol, for example: 2 s, 3p, 5d means s-sublevel of the second level, p-sublevel of the third level, d-sublevel of the fifth level.
The total number of sublevels at one level is equal to the level number n. The total number of orbitals at one level is equal to n 2. Accordingly, the total number of clouds in one layer is also equal to n 2 .
Designations: - free orbital (without electrons), - orbital with unpaired electron, - an orbital with an electron pair (with two electrons).
The order in which electrons fill the orbitals of an atom is determined by three laws of nature (the formulations are given in simplified terms):
1. Principle of least energy- electrons fill the orbitals in order of increasing energy of the orbitals.
2. Pauli principle- There cannot be more than two electrons in one orbital.
3. Hund's rule- within a sublevel, electrons first fill empty orbitals (one at a time), and only after that they form electron pairs.
The total number of electrons in the electronic level (or electron layer) is 2 n 2 .
The distribution of sublevels by energy is expressed as follows (in order of increasing energy):
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p ...
Examples electronic structure atoms:
Valence electrons- electrons of the atom that can take part in the formation chemical bonds. For any atom, these are all the outer electrons plus those pre-outer electrons whose energy is greater than that of the outer ones.
For example: the Ca atom has 4 outer electrons s 2, they are also valence; the Fe atom has 4 outer electrons s 2 but he has 3 d 6, therefore the iron atom has 8 valence electrons. Valence electronic formula of the calcium atom is 4 s 2, and iron atoms - 4 s 2 3d 6 .
Electrons
The concept of atom arose in the ancient world to designate particles of matter. Translated from Greek, atom means “indivisible.”
The Irish physicist Stoney, based on experiments, came to the conclusion that electricity is transferred by the smallest particles existing in the atoms of all chemical elements. In 1891, Stoney proposed calling these particles electrons, which means “amber” in Greek. A few years after the electron got its name, the English physicist Joseph Thomson and the French physicist Jean Perrin proved that electrons carry a negative charge. This is the smallest negative charge, which in chemistry is taken as one (-1). Thomson even managed to determine the speed of the electron (the speed of the electron in the orbit is inversely proportional to the orbital number n. The radii of the orbits increase in proportion to the square of the orbital number. In the first orbit of the hydrogen atom (n=1; Z=1) the speed is ≈ 2.2·106 m/ s, that is, about a hundred times less than the speed of light c = 3·108 m/s) and the mass of the electron (it is almost 2000 times less than the mass of the hydrogen atom).
State of electrons in an atom
The state of an electron in an atom is understood as a set of information about the energy of a particular electron and the space in which it is located. An electron in an atom does not have a trajectory of motion, i.e. we can only talk about the probability of finding it in the space around the nucleus.
It can be located in any part of this space surrounding the nucleus, and the totality of its various positions is considered as an electron cloud with a certain negative charge density. Figuratively, this can be imagined this way: if it were possible to photograph the position of an electron in an atom after hundredths or millionths of a second, as in a photo finish, then the electron in such photographs would be represented as dots. If countless such photographs were superimposed, the picture would be of an electron cloud with the greatest density where there would be the most of these points.
The space around the atomic nucleus in which an electron is most likely to be found is called an orbital. It contains approximately 90% electronic cloud, and this means that about 90% of the time the electron is in this part of space. They are distinguished by shape 4 currently known types of orbitals, which are designated by Latin letters s, p, d and f. Graphic representation Some forms of electron orbitals are shown in the figure.
The most important characteristic of the motion of an electron in a certain orbital is energy of its connection with the nucleus. Electrons with similar energy values form a single electron layer, or energy level. Energy levels are numbered starting from the nucleus - 1, 2, 3, 4, 5, 6 and 7.
The integer n, indicating the number of the energy level, is called the principal quantum number. It characterizes the energy of electrons occupying a given energy level. Electrons of the first energy level, closest to the nucleus, have the lowest energy. Compared to electrons of the first level, electrons of subsequent levels will be characterized by a large supply of energy. Consequently, the electrons of the outer level are least tightly bound to the atomic nucleus.
The largest number of electrons at an energy level is determined by the formula:
N = 2n 2 ,
where N is the maximum number of electrons; n is the level number, or the main quantum number. Consequently, the first energy level closest to the nucleus can contain no more than two electrons; on the second - no more than 8; on the third - no more than 18; on the fourth - no more than 32.
Starting from the second energy level (n = 2), each of the levels is divided into sublevels (sublayers), slightly different from each other in the binding energy with the nucleus. The number of sublevels is equal to the value of the main quantum number: the first energy level has one sublevel; the second - two; third - three; fourth - four sublevels. The sublevels, in turn, are formed by orbitals. Each valuen corresponds to the number of orbitals equal to n.
Sublevels are usually denoted by Latin letters, as well as the shape of the orbitals of which they consist: s, p, d, f.
Protons and Neutrons
An atom of any chemical element is comparable to a tiny solar system. Therefore, this model of the atom, proposed by E. Rutherford, is called planetary.
The atomic nucleus, in which the entire mass of the atom is concentrated, consists of particles of two types - protons and neutrons.
Protons have a charge equal to the charge of electrons, but opposite in sign (+1), and a mass equal to the mass of a hydrogen atom (it is taken as one in chemistry). Neutrons carry no charge, they are neutral and have a mass equal to the mass of a proton.
Protons and neutrons together are called nucleons (from the Latin nucleus - nucleus). The sum of the number of protons and neutrons in an atom is called the mass number. For example, the mass number of an aluminum atom is:
13 + 14 = 27
number of protons 13, number of neutrons 14, mass number 27
Since the mass of the electron, which is negligibly small, can be neglected, it is obvious that the entire mass of the atom is concentrated in the nucleus. Electrons are designated e - .
Since the atom electrically neutral, then it is also obvious that the number of protons and electrons in an atom is the same. It is equal to the serial number of the chemical element assigned to it in the Periodic Table. The mass of an atom consists of the mass of protons and neutrons. Knowing the atomic number of the element (Z), i.e. the number of protons, and the mass number (A), equal to the sum of the numbers of protons and neutrons, you can find the number of neutrons (N) using the formula:
N = A - Z
For example, the number of neutrons in an iron atom is:
56 — 26 = 30
Isotopes
Varieties of atoms of the same element that have the same nuclear charge but different mass numbers are called isotopes. Chemical elements found in nature are a mixture of isotopes. Thus, carbon has three isotopes with masses 12, 13, 14; oxygen - three isotopes with masses 16, 17, 18, etc. The relative atomic mass of a chemical element usually given in the Periodic Table is the average value of the atomic masses of a natural mixture of isotopes of a given element, taking into account their relative abundance in nature. Chemical properties The isotopes of most chemical elements are exactly the same. However, hydrogen isotopes differ greatly in properties due to a sharp multiple increase in their relative atomic mass; they are even given individual names and chemical symbols.
Elements of the first period
Diagram of the electronic structure of the hydrogen atom:
Diagrams of the electronic structure of atoms show the distribution of electrons across electronic layers (energy levels).
Graphic electronic formula of the hydrogen atom (shows the distribution of electrons by energy levels and sublevels):
Graphic electronic formulas of atoms show the distribution of electrons not only among levels and sublevels, but also among orbitals.
In a helium atom, the first electron layer is complete - it has 2 electrons. Hydrogen and helium are s-elements; The s-orbital of these atoms is filled with electrons.
For all elements of the second period the first electronic layer is filled, and electrons fill the s and p orbitals of the second electron layer in accordance with the principle of least energy (first s and then p) and the Pauli and Hund rules.
In the neon atom, the second electron layer is complete - it has 8 electrons.
For atoms of elements of the third period, the first and second electronic layers are completed, so the third electronic layer is filled, in which electrons can occupy the 3s-, 3p- and 3d-sublevels.
The magnesium atom completes its 3s electron orbital. Na and Mg are s-elements.
In aluminum and subsequent elements, the 3p sublevel is filled with electrons.
Elements of the third period have unfilled 3d orbitals.
All elements from Al to Ar are p-elements. The s- and p-elements form the main subgroups in the Periodic Table.
Elements of the fourth - seventh periods
A fourth electron layer appears in potassium and calcium atoms, and the 4s sublevel is filled, since it has lower energy than the 3d sublevel.
K, Ca - s-elements included in the main subgroups. For atoms from Sc to Zn, the 3d sublevel is filled with electrons. These are 3d elements. They are included in secondary subgroups, their outermost electronic layer is filled, and they are classified as transition elements.
Pay attention to the structure of the electronic shells of chromium and copper atoms. In them, one electron “fails” from the 4s to the 3d sublevel, which is explained by the greater energy stability of the resulting electronic configurations 3d 5 and 3d 10:
In the zinc atom, the third electron layer is complete - all sublevels 3s, 3p and 3d are filled in it, with a total of 18 electrons. In the elements following zinc, the fourth electron layer, the 4p sublevel, continues to be filled.
Elements from Ga to Kr are p-elements.
The krypton atom has an outer layer (fourth) that is complete and has 8 electrons. But there can be a total of 32 electrons in the fourth electron layer; the krypton atom still has unfilled 4d and 4f sublevels. For elements of the fifth period, sublevels are being filled in the following order: 5s - 4d - 5p. And there are also exceptions related to “ failure» electrons, y 41 Nb, 42 Mo, 44 Ru, 45 Rh, 46 Pd, 47 Ag.
In the sixth and seventh periods, f-elements appear, i.e., elements in which the 4f- and 5f-sublevels of the third outside electronic layer are filled, respectively.
4f elements are called lanthanides.
5f elements are called actinides.
The order of filling electronic sublevels in the atoms of elements of the sixth period: 55 Cs and 56 Ba - 6s elements; 57 La … 6s 2 5d x - 5d element; 58 Ce - 71 Lu - 4f elements; 72 Hf - 80 Hg - 5d elements; 81 T1 - 86 Rn - 6d elements. But here, too, there are elements in which the order of filling the electron orbitals is “violated,” which, for example, is associated with the greater energy stability of half and fully filled f-sublevels, i.e. nf 7 and nf 14. Depending on which sublevel of the atom is filled with electrons last, all elements are divided into four electron families, or blocks:
- s-elements. The s-sublevel of the outer level of the atom is filled with electrons; s-elements include hydrogen, helium and elements of the main subgroups of groups I and II.
- p-elements. The p-sublevel of the outer level of the atom is filled with electrons; p-elements include elements of the main subgroups of groups III-VIII.
- d-elements. The d-sublevel of the pre-external level of the atom is filled with electrons; d-elements include elements of secondary subgroups of groups I-VIII, i.e. elements of plug-in decades of large periods located between s- and p-elements. They are also called transition elements.
- f-elements. The f-sublevel of the third outer level of the atom is filled with electrons; these include lanthanides and antinoids.
The Swiss physicist W. Pauli in 1925 established that in an atom in one orbital there can be no more than two electrons having opposite (antiparallel) spins (translated from English as “spindle”), i.e., having such properties that conditionally can be imagined as the rotation of an electron around its imaginary axis: clockwise or counterclockwise.
This principle is called Pauli principle. If there is one electron in the orbital, then it is called unpaired; if there are two, then these are paired electrons, i.e. electrons with opposite spins. The figure shows a diagram of the division of energy levels into sublevels and the order in which they are filled.
Very often, the structure of the electronic shells of atoms is depicted using energy or quantum cells - so-called graphical electronic formulas are written. For this notation, the following notation is used: each quantum cell is designated by a cell that corresponds to one orbital; Each electron is indicated by an arrow corresponding to the spin direction. When writing a graphical electronic formula, you should remember two rules: Pauli's principle and F. Hund's rule, according to which electrons occupy free cells first one at a time and have the same spin value, and only then pair, but the spins, according to the Pauli principle, will already be in opposite directions.
Hund's rule and Pauli's principle
Hund's rule- a rule of quantum chemistry that determines the order of filling the orbitals of a certain sublayer and is formulated as follows: the total value of the spin quantum number of electrons of a given sublayer must be maximum. Formulated by Friedrich Hund in 1925.
This means that in each of the orbitals of the sublayer, one electron is first filled, and only after the unfilled orbitals are exhausted, a second electron is added to this orbital. In this case, in one orbital there are two electrons with half-integer spins of the opposite sign, which pair (form a two-electron cloud) and, as a result, the total spin of the orbital becomes equal to zero.
Another wording: Lower in energy lies the atomic term for which two conditions are satisfied.
- Multiplicity is maximum
- When the multiplicities coincide, the total orbital momentum L is maximum.
Let us analyze this rule using the example of filling p-sublevel orbitals p-elements of the second period (that is, from boron to neon (in the diagram below, horizontal lines indicate orbitals, vertical arrows indicate electrons, and the direction of the arrow indicates the spin orientation).
Klechkovsky's rule
Klechkovsky's rule - as the total number of electrons in atoms increases (with an increase in the charges of their nuclei, or the serial numbers of chemical elements), atomic orbitals are populated in such a way that the appearance of electrons in an orbital with a higher energy depends only on the main quantum number n and does not depend on all other quantum numbers numbers, including from l. Physically, this means that in a hydrogen-like atom (in the absence of interelectron repulsion), the orbital energy of an electron is determined only by the spatial distance of the electron charge density from the nucleus and does not depend on the characteristics of its motion in the field of the nucleus.
The empirical Klechkovsky rule and the ordering scheme that follows from it are somewhat contradictory to the real energy sequence of atomic orbitals only in two similar cases: for atoms Cr, Cu, Nb, Mo, Ru, Rh, Pd, Ag, Pt, Au, there is a “failure” of an electron with s -sublevel of the outer layer is replaced by the d-sublevel of the previous layer, which leads to an energetically more stable state of the atom, namely: after filling orbital 6 with two electrons s
8th grade
Lesson topic
"Structure of electronic shells of atoms."
Objective of the lesson:
Consideration of the model of atomic structure.
Introduction of the concept of “electron cloud”, “electron orbital”, “movement without trajectory”.
Consideration of the model of energy states of the atom.
Lesson objectives:
Educational: formation of an idea of the electronic shell of an atom and energy levels, consideration of the electronic structure of some elements, development of skills in compiling electronic formulas of atoms, determining elements by their electronic formulas, determining the composition of an atom.
Educational : consideration of the significance of the work of the Russian chemist D.I. Mendeleev;
Educational: developing the skills to work with the periodic table, think logically and formalize the results logical operations, draw parallels between the chemical concepts studied in the topic.
Lesson progress
Organizational aspects.
Good morning, guys, dear guests! My name is Irina Aleksandrovna Gubskaya, I am a chemistry teacher, I represent Ramensky municipal district, Udelninsky gymnasium.
Today, together we have to continue to comprehend the secrets and mysteries that the science of “chemistry” is full of. You only started studying this surprisingly interesting, but at the same time complex subject this year, but you probably already know a lot.
The topic of our lesson is “Structure of electronic shells of atoms” (we will write it down in notebooks).
Guys, do you want to see atoms, electrons?...Is it possible to do this?...
You can….in your imagination. Speculative. We see a lot of things speculatively, why not see an atom or an electron? Let's try it. So, let's go!
Our common task in class - To continue studying the topic “Atoms of chemical elements”, we will have to update our knowledge about the structure of the atom and get acquainted with the structure of the electronic shells of atoms.
2. Explanation of new material
The poet V. Bryusov in 1922, impressed by the amazing discoveries of physicists, wrote:
Perhaps these electrons
Worlds with five continents
Arts, knowledge, wars, thrones
And the memory of forty centuries!
Still, perhaps, every atom
A universe with a hundred planets;
There is everything that is here, in a compressed volume,
But also what is not here.
? How do you understand these lines?
Maybe... The similarity of electrons and atoms with astronomical objects has not yet been confirmed, but “what is not here” turned out to be more than enough, and you will learn about this in chemistry and physics lessons.
It took science more than 2,000 years to determine what it looked like. And even now he still remains a mystery to us.
I suggest you fill out the form on behalf of the atom.
Questionnaire.
1. Name Atom
2. Habitat any body in gaseous, liquid, solid state of aggregation
3. Amazing
quality incredible little
4. Atomic structure
? What does an atom consist of? (scheme)
An atom consists of a positively charged nucleus and electrons moving around it
? What does the nucleus of an atom consist of?
From protons and neutrons
And electrons moving around the nucleus form electron shell
At the beginning of the twentieth century. was accepted planetary model of atomic structure, according to which electrons move around the nucleus, like planets around the sun. Consequently, in an atom there are trajectories along which the electron moves. However, further research showed that there are no trajectories of electron motion in an atom. Motion without path means that we do not know how the electron moves in the atom, but we can determine the region where the electron is most likely to occur. This is no longer an orbit, but an orbital .
Moving around an atom, electrons combine to form it electron shell.
The set of all electrons surrounding a nucleus is called electronic shell ( write down the definition )
? Let's find out how electrons move around the nucleus?
? Randomly or in a certain order? It turns out that the movement of electrons occurs in a certain order.
The electrons in an atom differ in a certain energy, and, as experiments show, some are attracted to the nucleus more strongly, others less. This is explained by the distance of electrons from the nucleus. The closer the electrons are to the nucleus, the greater their connection with the nucleus, but the less energy they have. As you move away from the nucleus of an atom, the force of attraction of an electron to the nucleus decreases, and the energy reserve increases. Each electron, depending on its energy, will be at a certain distance from the nucleus. This is how they are formed electronic layers in the electron shell of the atom.
Each layer consists of electrons with similar energy values, so layers of electrons are calledenergy levels .
An electron layer consisting of electrons with similar energy values is called energy level. (we write down the definition)
? How can one determine how many layers (energy levels) there are in an atom of a particular element?
- The number of levels is determined by the number of the period in which the element is located.
For example:
N a -2 energy levels, because he is in period 2
N has 3, 3 period
Fe has 4, 4 period
? How many electrons can be in each energy level?
The maximum number of electrons that can be at a particular energy level is determined by the formula
N=2n2
Where N- maximum number of electrons per level;
n– energy level number.
For example:
1 energy level, n =1, N =2
n =2, N=8
Each level can hold no more than the calculated number of electrons.
If the electron layer contains the maximum possible number of electrons, then it is called completed. Electronic layers that do not contain the maximum number of electrons are called unfinished.
As was said earlier, an electron does not move in an orbit, but in an orbital and has no trajectory.
The space around the nucleus where it is most likely to be found electron is called the electron's orbital, or electron cloud.
(we write down the definition)
Orbitals, or sublevels, as they are also called, can have different shapes, and their number corresponds to the level number, but does not exceed four. The first energy level has one sublevel ( s), second - two ( s , p), third – three ( s , p , d), etc. Electrons located at the same energy level also differ from each other.
Electrons of different sublevels of the same level have different shapes
electronic cloud: spherical (s ), dumbbell-shaped (p ) and more complex configuration.
S - orbital- it's just a ball. The path of an electron along it resembles the path of a thread that is wound around a ball. Every level starts with it.
P – orbital looks like a voluminous figure eight or a twisted sausage, and the core is located along the twists. There are 3 such orbitals at each energy level, they are located at an angle of 90 - like coordinate axes.
D - orbital- these are two p-orbitals connected by centers - like a three-dimensional four-petal daisy; there can be 5 of them at a sublevel.
F – orbital has more complex shape, it is difficult to describe in words.
Imagine the path of your thoughts when solving a system of equations with 3 unknowns - it is about the same complexity.
Each orbital holds a maximum of 2 electrons with opposite spins.
Spin- this is the conditional direction of motion of the electron around its axis - it can be either clockwise or counterclockwise. Only electrons with different spins coexist in the same orbital, because their repulsion due to charges of the same name is partially extinguished.
Let's draw up a diagram of sequential filling of energy levels with electrons.
2 - 8 - 18 -
n=1 n=2 n=3
s s p s p d
2ē 2ē 6ē 2ē 6ē 8ē
Now we can compose diagram of the structure of electronic shells of atoms:
We determine the total number of electrons on the shell by the atomic number of the element.
We determine the number of energy levels in the electron shell. Their number is equal to the number of the period in D.I. Mendeleev’s table in which the element is located.
Determine the number of electrons at each energy level.
Using Arabic numerals to indicate the level and denoting the orbitals with the letters s and p, and the number of electrons of a given orbital with an Arabic numeral at the top right of the letter, we depict the structure of atoms with more complete electronic formulas.
Example:
The nucleus of a hydrogen atom has a charge of +1, so there is only one electron moving around its nucleus at a single energy level. Let's write down the electronic configuration of the hydrogen atom
Element No. 3 - lithium. The lithium nucleus has a charge of +3, therefore, there are three electrons in the lithium atom. Two of them are in the first energy level, and the third electron begins to fill the second energy level. First, the s orbital of the first level is filled, then the s orbital of the second level.
Element properties change periodically. All atoms of families of elements (alkali metals, halogens, noble gases) have the same number of electrons at the outer energy level.
Alkali metals have 1 electron
Halogens have 7 electrons
For noble gases, the outer level of their atoms is complete, 8 electrons
Conclusion: the properties of chemical elements repeat periodically (at certain intervals - periods) because the identical structure of the external energy levels of their atoms periodically repeats.
3. Consolidation
Option 1
The charge of the nucleus of a NITROGEN atom is equal to
A) 7 b)13 c)4 d)26 e)11
The number of protons in the nucleus of a KRYPTON atom is
A) 36 b)17 c)4 d)31 e)6
3 .The number of neutrons in the nucleus of a ZINC atom is equal to
a)8 b) 35 c)11 d)30 d)4
4 .The number of electrons in an IRON atom is
a)11 b)8 c)56 d) 26 e)30
Option 2
Maximum number of electrons at energy level 4
a) 32 b) 36 c) 16 d) 24
The number of electronic levels in a calcium atom is equal to
a)1 b)2 c)3 d)4
3. The number of electrons in the outer level of the BROMOINE atom is equal to
a) 7 b) 6 c)5 d)4
4. The total number of s-electrons in a LITHIUM atom is
a) 1 b)2 c)3 d)4
The electronic formula of the outer level 2s2 2p 6 corresponds to the atom
a) oxygen b) sulfur
c) fluorine d ) neon
Summing up. Reflection.
Homework : notes in notebooks, 8, ex. by cards
Homework:
1. Draw the structure of atoms of the following elements:
1 option
phosphorus
Option 2
Magnesium
2 . Compare the structure of atoms
1 option
boron and fluorine
Option 2
oxygen and sulfur
3 . Using data on the distribution of valence electrons, find the element:
A ) 2s 1
b ) 2s 2 2p 4
V ) 3s 2 3p 6
G ) 3d 10 4s 1
e) 4 s 2 4p 3
e) 4 s 2 4p 5
g) 3 s 2 3p 4
Let's summarize the lesson.
? What did we learn new today?
An electron has no trajectory and moves in an orbital.
Using the scheme of sequential filling of energy levels with electrons, we learned to compose electronic formulas of elements.
We learned how to determine a chemical element using electronic formulas.
“Far lies beyond the limits of our senses all nature began”
Titus Lucretius Carus
I century BC
In the quoted words of the ancient Roman poet, the entire difficulty of the structure of the atom is concentrated.
But we tried to describe it using mathematical approaches and formulas.
You have cards on your desks for self-assessment of the lesson. Please mark “+” or “-” your self-esteem. I was glad to meet you. Well done, you did a good job, I would like to say thank you for your cooperation. Goodbye, lesson is over, good luck in your chemistry studies.
An atom is the smallest particle of matter, consisting of a nucleus and electrons. The structure of the electronic shells of atoms is determined by the position of the element in the Periodic Table of Chemical Elements by D. I. Mendeleev.
Electron and electron shell of an atom
An atom, which is generally neutral, consists of a positively charged nucleus and a negatively charged electron shell (electron cloud), while the total positive and negative charges are equal in absolute value. When calculating the relative atomic mass, the mass of electrons is not taken into account, since it is negligible and 1840 times less than the mass of a proton or neutron.
Rice. 1. Atom.
An electron is a completely unique particle that has a dual nature: it has both the properties of a wave and a particle. They continuously move around the nucleus.
The space around the nucleus where the probability of finding an electron is most likely is called an electron orbital, or electron cloud. This space has a specific shape, which is designated by the letters s-, p-, d-, and f-. S-electron orbital has a spherical shape, the p-orbital has the shape of a dumbbell or a three-dimensional figure eight, the shapes of the d- and f-orbitals are much more complex.
Rice. 2. Shapes of electron orbitals.
Around the nucleus, electrons are arranged in electron layers. Each layer is characterized by its distance from the nucleus and its energy, which is why electronic layers are often called electronic energy levels. The closer the level is to the nucleus, the lower the energy of the electrons in it. One element differs from another in the number of protons in the nucleus of the atom and, accordingly, in the number of electrons. Consequently, the number of electrons in the electron shell of a neutral atom is equal to the number of protons contained in the nucleus of this atom. Every next element has one more proton in the nucleus, and one more electron in the electron shell.
The newly entering electron occupies the orbital with the lowest energy. However, the maximum number of electrons per level is determined by the formula:
where N is the maximum number of electrons, and n is the number of the energy level.
The first level can only have 2 electrons, the second can have 8 electrons, the third can have 18 electrons, and the fourth level can have 32 electrons. The outer level of an atom cannot contain more than 8 electrons: as soon as the number of electrons reaches 8, the next level, further from the nucleus, begins to be filled.
Structure of electronic shells of atoms
Each element stands in a certain period. A period is a horizontal collection of elements arranged in order of increasing charge of the nuclei of their atoms, which begins with an alkali metal and ends with an inert gas. The first three periods in the table are small, and the next ones, starting from fourth period– large, consist of two rows. The number of the period in which the element is located has physical meaning. It means how many electronic energy levels there are in an atom of any element of a given period. Thus, the element chlorine Cl is in the 3rd period, that is, its electron shell has three electronic layers. Chlorine is in group VII of the table, and in the main subgroup. The main subgroup is the column within each group that begins with period 1 or 2.
Thus, the state of the electron shells of the chlorine atom is as follows: the atomic number of the chlorine element is 17, which means that the atom has 17 protons in the nucleus and 17 electrons in the electron shell. At level 1 there can only be 2 electrons, at level 3 - 7 electrons, since chlorine is in the main subgroup of group VII. Then at level 2 there are: 17-2-7 = 8 electrons.
