Basic provisions of the atomic-molecular theory. Basic stoichiometric laws of chemistry. Laws of conservation of mass of matter, constancy of composition, volumetric ratios, Avogadro, equivalents. Molar mass of the 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 by chemical reactions.
There are gaps between molecules: gases have the largest, solids have the smallest.
Molecules move randomly and continuously.
The molecules of one substance have the same composition and properties, the molecules of 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- the type of atoms with the same positive charge of the nucleus.
Atoms of one element form molecules of a simple substance (02, H2, O3, Fe...). Atoms of different elements form molecules of a complex substance (H20, Na2SO4, FeClg...).
Law of conservation of mass
The mass of substances that entered into a chemical reaction is equal to the mass of substances formed as a result of the reaction.
scientists 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 by a 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 of molecular structure.
The composition of compounds of molecular structure, that is, consisting of molecules, is constant regardless of the method of preparation.
Law of Equivalents
Chemical elements combine with each other in strictly defined quantities corresponding to their equivalents.
An equivalent ratio means the same number of mole equivalents. That. the law of equivalents can be formulated differently: the number of mole equivalents for all substances participating in the reaction is the same.
Law of multiple ratios
Multiple ratios Dalton's law, 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 integers, 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 integers."
Consequence. Stoichiometric coefficients in the equations of chemical reactions for molecules of gaseous substances show in what volume ratios gaseous substances react or are obtained.
V 1: V 2: V 3 = v 1: v 2: v 3.
Periodic law and periodic system of elements of DIMendeleev. Basic ideas about the structure of the atom and the nucleus. Periodically changing and periodically unchanged properties of atoms and ions. Variants of the periodic table.
Periodic changes in the properties of chemical elements are due to the correct repetition of the electronic configuration of the external energy level (valence electrons) of their atoms with an increase in the nuclear charge.
The graphic representation of the 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 main quantum number of valence electrons.
The period number denotes the number of 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 with an alkali metal (s-element), and end with a noble gas (ns 2 np 6).
Metallic properties are considered as the ability of element atoms to easily give up electrons, while non-metallic properties are considered to accept electrons due to the tendency 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.
Secondary subgroups consist of elements of only large periods. Their valence electrons are 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 system 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 secondary subgroups),
f-elements (lanthanides, actinides).
The composition of the atom.
An atom consists of an atomic nucleus and an electron shell.
The nucleus of an atom is made up 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 denoted by the symbol Z and call charge number or atomic number (this is the serial number in the periodic table of Mendeleev). The nuclear charge is Ze, Where e is the elementary charge. The number of neutrons is denoted 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 denoted by the symbol , where X is the chemical symbol of the element. For example,
– hydrogen, – helium, – carbon, – oxygen, – uranium.
Isotope - a collection of atoms of the same element with the same number of neutrons in the nucleus (or a type of atoms 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 a single atom or isotope: (E - element symbol), for example: .
The structure of the electron shell of the atom
atomic orbital is the state of an electron in an atom. Orbital symbol - . Each orbital corresponds to an electron cloud.
The orbitals of real atoms in the ground (unexcited) state are of four types: s, p, d And f
Orbitals of the same level 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 the 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 in one level is equal to the level number n. The total number of orbitals in one level is n 2. Accordingly, the total number of clouds in one layer is also n 2 .
Designations: - free orbital (without electrons), - orbital with an unpaired electron, - 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 (formulations are given in a simplified way):
1. The principle of least energy- electrons fill the orbitals in order of increasing energy of the orbitals.
2. Pauli principle One orbital cannot contain more than two electrons.
3. Hund's rule- within the sublevel, electrons first fill free orbitals (one at a time), and only after that they form electron pairs.
The total number of electrons in the electronic level (or in the electronic layer) is 2 n 2 .
The distribution of sublevels by energy is expressed next (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 of the electronic structure of atoms:
Valence electrons- electrons of an atom that can take part in the formation of 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: Ca atom has 4 outer electrons s 2, they are also valence; the Fe atom has external electrons - 4 s 2 but he has 3 d 6, hence the iron atom has 8 valence electrons. The valence electronic formula of the calcium atom is 4 s 2, and iron atoms - 4 s 2 3d 6 .
Let us mentally take an atom of any chemical element. What states are the electrons in? It is clear from the previous paragraph that for each electron it is necessary to know the values of four quantum numbers that characterize its state. But we don't yet know how many electrons are in each state. Which conditions are more and which are less likely? These questions are answered by two important principle(law). The first of them was discovered in 1925 by the Swiss physicist V. Pauli (1900-1958) and named after him - the Pauli principle.
All electrons in an atom are in different states, i.e. are characterized by different sets of four quantum numbers.
In this case, the concept of "principle" denotes one of the fundamental laws of nature, which makes the atom what it is - a microparticle of matter with an individual electronic structure for each chemical element. The role of the Pauli principle in nature becomes clearer if we imagine that it does not work. Then the electronic environment of the atomic nucleus loses structural certainty. All electrons roll into some one most favorable state.
It should be noted that this law is valid for all fermions.
A corollary follows from the Pauli principle, which determines the capacity of the orbital, i.e. the number of electrons that can form a single electron cloud. By choosing any of the orbitals, we fix the first three quantum numbers. For example, for an orbital 2 r 2:p = 2, /= 1, mj= 0. But you can also change the spin quantum number m s Two sets of quantum numbers are obtained:
Therefore, an orbital can hold no more than two electrons, and atoms can have one- and two-electron clouds.
Two electrons in the same orbital are called an electron pair.
Knowing the capacity of the orbital, it is easy to understand that the capacity of the energy sublevel is equal to twice the number of orbitals (Table 5.1).
Table 5.1
Structure of sublevels in atoms
A set of electrons of one energy sublevel is called a subshell of an atom.
The capacity of the energy level is the sum of the capacity of the sublevels (Table 5.2). In the first column of the table, in addition to the values of the main quantum number, there are letter designations for the electron shells of the atom.
Table 5.2
The structure of energy levels in atoms
A set of electrons of the same energy level is called the shell of an atom.
The real filling ("settlement") of orbitals, sublevels and levels with electrons determines the second principle - the principle of least energy.
The ground (stable) state of an atom corresponds to the minimum total energy of electrons.
The states of an atom with increased energy are called excited. An atom in an excited state is unstable in the sense that in a very short time (~10 -8 s) it passes into the ground state, radiating energy quanta.
Any physical system is the more stable, the lower its potential energy. Therefore, we invariably observe that a thrown body hits the ground or rolls down a hill, a bent spring straightens, and so on. Also, the electron shells of atoms are in a stable state if the total energy of the electrons is minimal. We already know the set of possible energy states of an atom (see Fig. 5.7). Let us consider how the corresponding sublevels and levels are populated by electrons. In this case, the Pauli principle is strictly observed, which has priority over the principle of least energy and is not violated. We will depict the electronic structure of atoms using energy diagrams and electronic formulas. The energy diagram is a part of the general sequence of sublevels (see Fig. 5.7), containing populated sublevels. The electronic formula lists the occupied sublevels in ascending order of energy, with superscripts indicating the number of electrons. The first two elements of the periodic system can be represented by diagrams I and II. The diagram shows that the position of the 1n* level in the helium atom is lower than in the hydrogen atom, since helium has a larger nuclear charge and electrons are more strongly attracted to the nucleus. The capacity of the first energy level in the helium atom is exhausted.
In the elements following helium, the second energy level is populated. Consider the energy diagrams of the three nearest elements - lithium, beryllium and boron (diagrams III, IV and V).
In lithium and beryllium, the sublevel is populated 2s. The fifth electron of the boron atom begins to populate sublevel 2 R according to the Pauli principle. At carbon and nitrogen atoms, the population of this sublevel continues (diagrams VI and VII).
In the structure of these elements, another important regularity in the formation of electron shells is manifested - Hund's rule (1927).
The basic) 7 state of the atom corresponds to the population of electrons of the maximum number of energetically equivalent orbitals. In this case, the electrons have the same values of spin quantum numbers (all +1/2 or all -1/2).
When considering the energy diagram of an atom, it seems that the transfer of an electron between identical orbitals 2 R does not change its energy. In fact, when electrons move in different orbitals, the repulsion between them decreases, due to which the potential energy still decreases. Electrons occupying single orbitals are called unpaired. Further, when studying the nature of chemical bonds, we will see that the valence of atoms is determined by the number of unpaired electrons. Nitrogen has three unpaired electrons and is indeed trivalent. Suffice it to recall the formula for ammonia NH 3. Carbon, according to the diagram, is divalent. However, upon absorption of a relatively small energy, one electron is transferred from sublevel 25 to sublevel 2r. Carbon goes into an excited state with the electronic formula s 2 2s ( 2p s . In this state, it has four unpaired electrons. A free atom can only be in an excited state for a very short time. But, being in the composition of the molecule, the atom receives additional electrons to populate the orbitals. After that, the possibility of transition to the ground state is excluded, and the carbon atom remains tetravalent. In fact, the energy spent on excitation of an electron is compensated by the energy of formation of additional chemical bonds.
Population of 2p orbitals by second electrons occurs in oxygen, fluorine, and neon (diagrams VIII, IX, X). In this case, the number of remaining unpaired electrons and, accordingly, the valency of atoms decreases successively. This corresponds to elementary knowledge about the properties of oxygen, fluorine and neon: oxygen is bivalent, fluorine is monovalent, and neon does not form chemical bonds, i.e. its valency is zero.
We have seen that the elements from lithium to neon have a second energy level populated by electrons, and that is why they are
- 2nd period of the periodic table. At the sodium following neon, the population of the third energy level begins, and then
- 3rd period as sublevels 35 and 3 are populated R. Energy diagrams and electronic formulas of elements from sodium to argon can be represented in an abbreviated form, designating the repeating set of neon electrons in them as. The meaning of the abbreviated electronic formula is that only the valence electrons of the atom are indicated in it. The rest of the electrons that make up electron core of an atom, are of secondary importance for chemistry. As an example, let's write abbreviated formulas and diagrams for sodium, silicon and argon (diagrams XI, XII and XIII).
The number of chemical elements in the 2nd and 3rd periods is determined by the total capacity of the 5- and /^-sublevels, which is eight electrons. Thus, the presence of exactly eight groups in the periodic table receives a physical explanation. The reason for the observed similarity of chemical elements in groups also becomes clear. Comparing the energy diagrams of elements of the same group - lithium and sodium, carbon and silicon, etc. - we notice that they are characterized by the same population of the external energy level. From this follows, first of all, the same valence of atoms, which is the reason for the similarity of chemical properties. But the electronic structures of atoms, taken as a whole, are different. From period to period, the number of electron shells increases, which entails an increase in the atomic radii. Therefore, as already noted, along with the similarity, there is also a certain direction in the change in properties.
From the electronic formulas and energy diagrams of atoms, it is obvious that in groups IA and PA, electrons fill the outer 5-sublevel, and in groups I HA-V111A, the outer p-sublevel. This provides a basis for classifying chemical elements into blocks. The first two groups are considered as block of s-elements, and groups from ША to VIIIА - as block of p-elements.
In the periodic table there are more groups with the same numbers, but with the addition of the symbol "B". How is the existence of these groups explained? From fig. 5.6 it is obvious that the sublevel 3d energy is between sublevels 45 and 4 R. In the periodic table, the 4th period, like the previous ones, begins with two 5-elements - potassium ([Ar] 45 l) and calcium (fAr] 4l 2). After calcium, the settlement of a non-sublevel begins R, as in the 2nd and 3rd periods, and the sublevel 3d, which has a capacity of 10 electrons. Electrons at the ^-sublevel appear one after another in scandium and the elements following it, including zinc. They are included in block of d-elements. The numbering of groups of d-elements is based on the fact that in groups III to VIII there is the same number of electrons in the two upper sublevels of both p-elements (5- and p-sublevels) and d-elements (5- and d- sublevels). Groups IB and PV are numbered according to the population of the outer 5-sublevel, like 5-elements.
The fourth period is completed by p-elements following zinc. The filled Zr/-nolevel in them is energetically stabilized and becomes lower than the sublevel As. This is explained by the different course of lowering the energy of the orbitals of the 45- and 3^/-sublevels as the charge of the atomic nucleus increases (Fig. 5.9).
Rice. 5.9.
Example 5.1. Write the abbreviated electronic formulas for iron and krypton.
Solution. For both iron and krypton, the nearest antecedent noble gas is argon (Z = 18). Iron (Z = 26) has eight electrons left to fill the upper 45 and 36/ sublevels. We write the formula 45 2 3rf 6 . Krypton (Z = 36) has 10 more electrons added, which completely populate the sublevels 3d And Ar. Filled 3d-set the sublevel in the formula up to the 45th sublevel: [Ar]3 10 45 2 4/? 6.
The fifth period of the periodic table is similar in structure to the fourth. Both of them contain 18 chemical elements. In the 5th period, rubidium and strontium belong to the 5-block of elements, 10 elements from yttrium to cadmium belong to the d-block and the remaining six elements from indium to xenon belong to R- block.
This is followed by the longest 6th and 7th periods containing but 32 elements. In the 6th period, a family of 14 chemical elements is added - from lanthanum to ytterbium, called lanthanides, and in the 7th - a similar family actinides - from actinium to nobelium. In their atoms, the 4/- and 5/-sublevels are filled with electrons, respectively. The lanthanides and actinides make up the block of /-elements. Due to the special characteristics of the orbitals of the / sublevels, all lanthanides and all actinides exhibit a great similarity in chemical properties.
Example 5.2. What explains why families of /-elements contain 14 chemical elements each?
Solution. In accordance with the formula 2/+1 sublevel f(1=3) consists of seven orbitals. Therefore, its capacity is 14 electrons, and the gradual filling of the /-sublevel occurs in 14 chemical elements.
Thus, a brief review of the electronic structure of atoms in general terms reveals the physical basis for the periodicity of changes in the properties of chemical elements and, consequently, the periodic law of D. I. Mendeleev. Briefly, we can say that the periodic law is a consequence of the Pauli principle and the principle of least energy.
8th grade
Lesson topic
"The structure of the electron shells of atoms".
The purpose of the lesson:
Consideration of the model of the structure of the atom.
Introduction of the concept of "electron cloud", "electronic orbital", "motion without a trajectory".
Consideration of the model of the energy states of the atom.
Lesson objectives:
Educational: formation of an idea about the electron 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;
Developing: the formation of skills to work with the periodic system, to think logically and draw up the results of logical operations, to draw parallels between the chemical concepts studied in the topic.
During the classes
organizational moments.
Good morning guys, dear guests! My name is Irina Aleksandrovna Gubskaya, I am a chemistry teacher, I represent the Ramensky municipal district, the Udelnaya gymnasium.
Today, together we have to continue to comprehend the secrets and mysteries that the science of “chemistry” is full of. You only this year began to study this surprisingly interesting, but at the same time complex subject, but you probably already know a lot.
The topic of our lesson is “The structure of the electron shells of atoms” (we will write it down in notebooks).
Guys, do you want to see atoms, electrons?... Can this be done?...
You can .... in the imagination. Speculative. We see a lot of things speculatively, why not see an atom or an electron? Let's try. So, go!
Our common goal in the classroom is to continue studying the topic "Atoms of chemical elements", we have to update knowledge about the structure of the atom and get acquainted with the structure of the electron 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 where there are five continents,
Arts, knowledge, wars, thrones
And the memory of forty centuries!
Also, perhaps every atom
Universe, where one hundred planets;
There - 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 over 2,000 years to figure out what it looks like. And even now it is still a mystery to us.
I suggest you fill out a questionnaire on behalf of the atom.
Questionnaire.
1. Name Atom
2. Habitat any body in a gaseous, liquid, solid state of aggregation
3. Striking
quality incredible smallness
4. The structure of the atom
? What is an atom made of? (scheme)
An atom consists of a positively charged nucleus and electrons moving around it.
? What is the nucleus of an atom made of?
From protons and neutrons
And electrons moving around the nucleus form electron shell
At the beginning of the twentieth century. was adopted planetary model of the structure of the atom, according to which electrons move around the nucleus, like planets around the sun. Therefore, in an atom there are trajectories along which an electron moves. However, further studies showed that there are no trajectories of electrons in the atom. Movement without a trajectory means that we do not know how the electron moves in the atom, but we can determine the region where the electron is most often encountered. It's not an orbit, it's an orbital .
Moving around the atom, the electrons together form its electron shell.
The totality of all electrons surrounding the nucleus is called electron 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.
Electrons in an atom differ in a certain energy, and, as experiments show, some are attracted to the nucleus more strongly, others weaker. This is explained by the remoteness of electrons from the nucleus. The closer the electrons to the nucleus, the greater their bond with the nucleus, but the less energy. As the distance from the nucleus of the atom, the force of attraction of the electron to the nucleus decreases, and the energy supply increases. Each electron, depending on its energy, will be at a certain distance from the nucleus. This is how electronic layers in the electron shell of an atom.
Each layer consists of electrons with close energy values, so the layers of electrons are calledenergy levels .
An electron layer consisting of electrons with close energy values is called energy level. (write down the definition)
? But how to determine how many layers (energy levels) are in the atom of an 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 it is in period 2
N - 3, 3 period
Fe - 4, 4 period
? How many electrons can be in each energy level?
The maximum number of electrons that can be in a particular energy level is determined by the formula
N = 2n2
Where N is the 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. The electron layers that do not contain the maximum number of electrons are called unfinished.
As previously mentioned, the electron does not move in an orbit, but in an orbit and has no trajectory.
The space around the nucleus where it is most likely to find a given electron is called the orbital of this electron, or electron cloud.
(write down the definition)
Orbitals, or sublevels, as they are also called, can have a different shape, and their number corresponds to the level number, but does not exceed four. The first energy level has one sublevel ( s), the second - two ( s , p), the third - three ( s , p , d) etc. Electrons that are at the same energy level also differ from each other.
Electrons of different sublevels of the same level have different shapes
electron 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. It starts every level.
P – orbital looks like a voluminous figure eight or a twisted sausage, and the core is located along the twist. There are -3 such orbitals at each energy level, they are located at an angle of 90 - as coordinate axes.
D - orbital- these are two p-orbitals connected by centers - like a voluminous four-petal daisy, there can be 5 of them at a sublevel.
F – orbital has a more complex form, it is difficult to describe in words.
Imagine the path of your thought when solving a system of equations with 3 unknowns - this is about the same complexity.
Each orbital holds a maximum of 2 electrons with opposite spins.
Spin- this is the conditional direction of electron movement 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 like charges is partially extinguished.
Let us draw up a scheme of successive filling of energy levels with electrons.
2nd 8th 18th
n=1 n=2 n=3
s s p s p d
2nd 2nd 6th 2nd 6th 8th
Now we can compose diagram of the structure of the electron shells of atoms:
We determine the total number of electrons on the shell by the ordinal 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 the table of D. I. Mendeleev, in which the element is located.
Determine the number of electrons in each energy level.
Using Arabic numerals to designate the level and designating the orbitals with the letters s and p, and the number of electrons of a given orbital with an Arabic numeral in the upper right above 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 only one electron moves around its nucleus at a single energy level. Let's write down the electronic configuration of the hydrogen atom
Element number 3 - lithium. The lithium nucleus has a charge of +3, therefore, there are three electrons in the lithium atom. Two of them are at 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 the element families (alkali metals, halogens, noble gases) have the same number of electrons at the external energy level.
Alkali metals have 1 electron
Halogens have 7 electrons
Noble gases have the outer level of their atoms completed, 8 electrons
Conclusion: the properties of chemical elements periodically (at certain intervals - periods) repeat because the same structure of the external energy levels of their atoms is periodically repeated.
3. Fixing
Option 1
The charge of the nucleus of the NITROGEN atom is equal to
A) 7 b)13 c)4 d)26 e)11
The number of protons in the nucleus of an atom of KRYPTO is equal to
A) 36 b)17 c)4 d)31 e)6
3 .The number of neutrons in the nucleus of a ZINC atom is
a) 8 b) 35 c) 11 d) 30 e) 4
4 .The number of electrons in an IRON atom is
a) 11 b) 8 c) 56 d) 26 e) 30
Option 2
The maximum number of electrons in the 4th energy level
a) 32 b) 36 c) 16 d) 24
The number of electronic levels in a calcium atom is
a)1 b)2 c)3 d)4
3. The number of electrons at the outer level of the BROMINE atom is
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 g ) not she
Summarizing. Reflection.
Homework: Notebook entries, 8, ex. by cards
Homework:
1. Draw the structure of the 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 . Based 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?
The electron does not have a trajectory and its movement occurs in an orbit.
According to the scheme of sequential filling of energy levels with electrons, they learned how to compose electronic formulas of elements.
We learned how to determine a chemical element using electronic formulas.
"Far lies beyond our senses the whole nature of beginnings"
Titus Lucretius Kar
1st century BC.
In the above words of the ancient Roman poet, all the difficulty of the structure of the atom is concentrated.
But we tried to describe it using mathematical approaches and formulas.
You have cards on the tables for self-assessment of the lesson. Please mark "+" or "-" your self-assessment. I was glad to meet you. Well done, you did a good job, I would like to note, thank you for your cooperation. Goodbye, the lesson is over, good luck with your study of chemistry.
The outstanding Danish physicist Niels Bohr (Fig. 1) suggested that electrons in an atom can move not along any, but along strictly defined orbits.
The electrons in an atom differ in their energy. As experiments show, some of them are attracted to the nucleus more strongly, others - weaker. The main reason for this is the different removal of electrons from the nucleus of an atom. The closer the electrons are to the nucleus, the stronger they are bound to it and the more difficult it is to pull them out of the electron shell. Thus, as the distance from the nucleus of the atom increases, the energy of the electron increases.
Electrons moving near the nucleus, as it were, block (shield) the nucleus from other electrons, which are attracted to the nucleus weaker and move at a greater distance from it. This is how electronic layers are formed.
Each electron layer consists of electrons with close energy values; Therefore, the electronic layers are also called energy levels.
The nucleus is located in the center of the atom of each element, and the electrons that form the electron shell are placed around the nucleus in layers.
The number of electron layers in an atom of an element is equal to the number of the period in which the element is located.
For example, sodium Na is an element of the 3rd period, which means that its electron shell includes 3 energy levels. There are 4 energy levels in the bromine atom Br, since bromine is located in the 4th period (Fig. 2).
Sodium atom model: Bromine atom model:
The maximum number of electrons in an energy level is calculated by the formula: 2n 2 , where n is the number of the energy level.
Thus, the maximum number of electrons per:
3rd layer - 18 etc.
For elements of the main subgroups, the number of the group to which the element belongs is equal to the number of external electrons of the atom.
The outer electrons are called the last electron layer.
For example, in a sodium atom there is 1 external electron (because it is an element of the IA subgroup). The bromine atom has 7 electrons on the last electron layer (this is an element of the VIIA subgroup).
The structure of the electron shells of elements of 1-3 periods
In the hydrogen atom, the nuclear charge is +1, and this charge is neutralized by a single electron (Fig. 3).
The next element after hydrogen is helium, also an element of the 1st period. Therefore, there is 1 energy level in the helium atom, on which two electrons are located (Fig. 4). This is the maximum possible number of electrons for the first energy level.
Element #3 is lithium. There are 2 electron layers in the lithium atom, since this is an element of the 2nd period. On the 1st layer in the lithium atom there are 2 electrons (this layer is completed), and on the 2nd layer - 1 electron. The beryllium atom has 1 more electron than the lithium atom (Fig. 5).
Similarly, it is possible to depict the schemes of the structure of atoms of the remaining elements of the second period (Fig. 6).
In the atom of the last element of the second period - neon - the last energy level is complete (it has 8 electrons, which corresponds to the maximum value for the 2nd layer). Neon is an inert gas that does not enter into chemical reactions, therefore, its electron shell is very stable.
American chemist Gilbert Lewis gave an explanation and put forward octet rule, according to which the eight-electron layer is stable(with the exception of 1 layer: since it can contain no more than 2 electrons, a two-electron state will be stable for it).
Neon is followed by an element of the 3rd period - sodium. There are 3 electron layers in the sodium atom, on which 11 electrons are located (Fig. 7).
Rice. 7. Scheme of the structure of the sodium atom
Sodium is in group 1, its valency in compounds is I, like that of lithium. This is due to the fact that there is 1 electron on the outer electron layer of sodium and lithium atoms.
The properties of the elements are periodically repeated because the atoms of the elements periodically repeat the number of electrons in the outer electron layer.
The structure of the atoms of the remaining elements of the third period can be represented by analogy with the structure of the atoms of the elements of the 2nd period.
The structure of the electron shells of elements 4 periods
The fourth period includes 18 elements, among them there are elements of both the main (A) and secondary (B) subgroups. A feature of the structure of atoms of the elements of side subgroups is that they sequentially fill the pre-external (internal), and not external, electronic layers.
The fourth period begins with potassium. Potassium is an alkali metal that exhibits valence I in compounds. This is in complete agreement with the following structure of its atom. As an element of the 4th period, the potassium atom has 4 electron layers. The last (fourth) electronic layer of potassium has 1 electron, the total number of electrons in a potassium atom is 19 (the serial number of this element) (Fig. 8).
Rice. 8. Scheme of the structure of the potassium atom
Calcium follows potassium. The calcium atom on the outer electron layer will have 2 electrons, like beryllium and magnesium (they are also elements of the II A subgroup).
The next element after calcium is scandium. This is an element of the secondary (B) subgroup. All elements of the secondary subgroups are metals. A feature of the structure of their atoms is the presence of no more than 2 electrons on the last electron layer, i.e. sequentially filled with electrons will be the penultimate electron layer.
So, for scandium, we can imagine the following model of the structure of the atom (Fig. 9):
Rice. 9. Scheme of the structure of the scandium atom
Such a distribution of electrons is possible, since the maximum allowable number of electrons on the third layer is 18, i.e. eight electrons on the 3rd layer is a stable, but not complete, state of the layer.
In ten elements of the secondary subgroups of the 4th period from scandium to zinc, the third electron layer is successively filled.
The scheme of the structure of the zinc atom can be represented as follows: on the outer electron layer - two electrons, on the pre-outer layer - 18 (Fig. 10).
Rice. 10. Scheme of the structure of the zinc atom
The elements following zinc belong to the elements of the main subgroup: gallium, germanium, etc. up to krypton. In the atoms of these elements, the 4th (i.e., outer) electron layer is successively filled. In an atom of an inert gas of krypton there will be an octet on the outer shell, i.e., a stable state.
Summing up the lesson
In this lesson, you learned how the electron shell of an atom is arranged and how to explain the phenomenon of periodicity. We got acquainted with the models of the structure of the electron shells of atoms, with the help of which it is possible to predict and explain the properties of chemical elements and their compounds.
Bibliography
- Orzhekovsky P.A. Chemistry: 8th grade: textbook for general education. inst. / P.A. Orzhekovsky, L.M. Meshcheryakova, M.M. Shalashova. - M.: Astrel, 2013. (§44)
- Rudzitis G.E. Chemistry: inorgan. chemistry. Organ. chemistry: textbook. for 9 cells. / G.E. Rudzitis, F.G. Feldman. - M.: Enlightenment, JSC "Moscow textbooks", 2009. (§37)
- Khomchenko I.D. Collection of problems and exercises in chemistry for high school. - M.: RIA "New Wave": Publisher Umerenkov, 2008. (p. 37-38)
- Encyclopedia for children. Volume 17. Chemistry / Chapter. ed. V.A. Volodin, leading. scientific ed. I. Leenson. - M.: Avanta +, 2003. (p. 38-41)
- Chem.msu.su().
- Dic.academic.ru ().
- Krugosvet.ru ().
Homework
- With. 250 Nos. 2-4 from the textbook P.A. Orzhekovsky "Chemistry: 8th grade" / P.A. Orzhekovsky, L.M. Meshcheryakova, M.M. Shalashova. - M.: Astrel, 2013.
- Write down the distribution of electrons over layers in an atom of argon and krypton. Explain why the atoms of these elements enter into chemical interaction with great difficulty.
The outstanding Danish physicist Niels Bohr (Fig. 1) suggested that electrons in an atom can move not along any, but along strictly defined orbits.
The electrons in an atom differ in their energy. As experiments show, some of them are attracted to the nucleus more strongly, others - weaker. The main reason for this is the different removal of electrons from the nucleus of an atom. The closer the electrons are to the nucleus, the stronger they are bound to it and the more difficult it is to pull them out of the electron shell. Thus, as the distance from the nucleus of the atom increases, the energy of the electron increases.
Electrons moving near the nucleus, as it were, block (shield) the nucleus from other electrons, which are attracted to the nucleus weaker and move at a greater distance from it. This is how electronic layers are formed.
Each electron layer consists of electrons with close energy values; Therefore, the electronic layers are also called energy levels.
The nucleus is located in the center of the atom of each element, and the electrons that form the electron shell are placed around the nucleus in layers.
The number of electron layers in an atom of an element is equal to the number of the period in which the element is located.
For example, sodium Na is an element of the 3rd period, which means that its electron shell includes 3 energy levels. There are 4 energy levels in the bromine atom Br, since bromine is located in the 4th period (Fig. 2).
Sodium atom model: Bromine atom model:
The maximum number of electrons in an energy level is calculated by the formula: 2n 2 , where n is the number of the energy level.
Thus, the maximum number of electrons per:
3rd layer - 18 etc.
For elements of the main subgroups, the number of the group to which the element belongs is equal to the number of external electrons of the atom.
The outer electrons are called the last electron layer.
For example, in a sodium atom there is 1 external electron (because it is an element of the IA subgroup). The bromine atom has 7 electrons on the last electron layer (this is an element of the VIIA subgroup).
The structure of the electron shells of elements of 1-3 periods
In the hydrogen atom, the nuclear charge is +1, and this charge is neutralized by a single electron (Fig. 3).
The next element after hydrogen is helium, also an element of the 1st period. Therefore, there is 1 energy level in the helium atom, on which two electrons are located (Fig. 4). This is the maximum possible number of electrons for the first energy level.
Element #3 is lithium. There are 2 electron layers in the lithium atom, since this is an element of the 2nd period. On the 1st layer in the lithium atom there are 2 electrons (this layer is completed), and on the 2nd layer - 1 electron. The beryllium atom has 1 more electron than the lithium atom (Fig. 5).
Similarly, it is possible to depict the schemes of the structure of atoms of the remaining elements of the second period (Fig. 6).
In the atom of the last element of the second period - neon - the last energy level is complete (it has 8 electrons, which corresponds to the maximum value for the 2nd layer). Neon is an inert gas that does not enter into chemical reactions, therefore, its electron shell is very stable.
American chemist Gilbert Lewis gave an explanation and put forward octet rule, according to which the eight-electron layer is stable(with the exception of 1 layer: since it can contain no more than 2 electrons, a two-electron state will be stable for it).
Neon is followed by an element of the 3rd period - sodium. There are 3 electron layers in the sodium atom, on which 11 electrons are located (Fig. 7).
Rice. 7. Scheme of the structure of the sodium atom
Sodium is in group 1, its valency in compounds is I, like that of lithium. This is due to the fact that there is 1 electron on the outer electron layer of sodium and lithium atoms.
The properties of the elements are periodically repeated because the atoms of the elements periodically repeat the number of electrons in the outer electron layer.
The structure of the atoms of the remaining elements of the third period can be represented by analogy with the structure of the atoms of the elements of the 2nd period.
The structure of the electron shells of elements 4 periods
The fourth period includes 18 elements, among them there are elements of both the main (A) and secondary (B) subgroups. A feature of the structure of atoms of the elements of side subgroups is that they sequentially fill the pre-external (internal), and not external, electronic layers.
The fourth period begins with potassium. Potassium is an alkali metal that exhibits valence I in compounds. This is in complete agreement with the following structure of its atom. As an element of the 4th period, the potassium atom has 4 electron layers. The last (fourth) electronic layer of potassium has 1 electron, the total number of electrons in a potassium atom is 19 (the serial number of this element) (Fig. 8).
Rice. 8. Scheme of the structure of the potassium atom
Calcium follows potassium. The calcium atom on the outer electron layer will have 2 electrons, like beryllium and magnesium (they are also elements of the II A subgroup).
The next element after calcium is scandium. This is an element of the secondary (B) subgroup. All elements of the secondary subgroups are metals. A feature of the structure of their atoms is the presence of no more than 2 electrons on the last electron layer, i.e. sequentially filled with electrons will be the penultimate electron layer.
So, for scandium, we can imagine the following model of the structure of the atom (Fig. 9):
Rice. 9. Scheme of the structure of the scandium atom
Such a distribution of electrons is possible, since the maximum allowable number of electrons on the third layer is 18, i.e. eight electrons on the 3rd layer is a stable, but not complete, state of the layer.
In ten elements of the secondary subgroups of the 4th period from scandium to zinc, the third electron layer is successively filled.
The scheme of the structure of the zinc atom can be represented as follows: on the outer electron layer - two electrons, on the pre-outer layer - 18 (Fig. 10).
Rice. 10. Scheme of the structure of the zinc atom
The elements following zinc belong to the elements of the main subgroup: gallium, germanium, etc. up to krypton. In the atoms of these elements, the 4th (i.e., outer) electron layer is successively filled. In an atom of an inert gas of krypton there will be an octet on the outer shell, i.e., a stable state.
Summing up the lesson
In this lesson, you learned how the electron shell of an atom is arranged and how to explain the phenomenon of periodicity. We got acquainted with the models of the structure of the electron shells of atoms, with the help of which it is possible to predict and explain the properties of chemical elements and their compounds.
Bibliography
- Orzhekovsky P.A. Chemistry: 8th grade: textbook for general education. inst. / P.A. Orzhekovsky, L.M. Meshcheryakova, M.M. Shalashova. - M.: Astrel, 2013. (§44)
- Rudzitis G.E. Chemistry: inorgan. chemistry. Organ. chemistry: textbook. for 9 cells. / G.E. Rudzitis, F.G. Feldman. - M.: Enlightenment, JSC "Moscow textbooks", 2009. (§37)
- Khomchenko I.D. Collection of problems and exercises in chemistry for high school. - M.: RIA "New Wave": Publisher Umerenkov, 2008. (p. 37-38)
- Encyclopedia for children. Volume 17. Chemistry / Chapter. ed. V.A. Volodin, leading. scientific ed. I. Leenson. - M.: Avanta +, 2003. (p. 38-41)
- Chem.msu.su().
- Dic.academic.ru ().
- Krugosvet.ru ().
Homework
- With. 250 Nos. 2-4 from the textbook P.A. Orzhekovsky "Chemistry: 8th grade" / P.A. Orzhekovsky, L.M. Meshcheryakova, M.M. Shalashova. - M.: Astrel, 2013.
- Write down the distribution of electrons over layers in an atom of argon and krypton. Explain why the atoms of these elements enter into chemical interaction with great difficulty.
