External energy levels: structural features and their role in interactions between atoms. Change in the number of electrons at the external energy level of atoms of chemical elements - Knowledge Hypermarket How to identify atoms at the external level

An atom is an electrically neutral particle consisting of a positively charged nucleus and a negatively charged electron shell. The nucleus is located at the center of the atom and consists of positively charged protons and uncharged neutrons held together by nuclear forces. The nuclear structure of the atom was experimentally proven in 1911 by the English physicist E. Rutherford.

The number of protons determines the positive charge of the nucleus and is equal to the atomic number of the element. The number of neutrons is calculated as the difference between the atomic mass and the atomic number of the element. Elements that have the same nuclear charge (same number of protons) but different atomic mass (different number of neutrons) are called isotopes. The mass of an atom is mainly concentrated in the nucleus, because the negligible mass of electrons can be neglected. Atomic mass equal to the sum of the masses of all protons and all neutrons of the nucleus.
A chemical element is a type of atom with the same nuclear charge. There are currently 118 known chemical elements.

All the electrons of an atom form its electron shell. The electron shell has a negative charge equal to the total number of electrons. The number of electrons in the shell of an atom coincides with the number of protons in the nucleus and is equal to the atomic number of the element. The electrons in the shell are distributed among the electronic layers according to energy reserves (electrons with similar energy values ​​form one electron layer): electrons with lower energy are closer to the nucleus, electrons with higher energy are further from the nucleus. The number of electronic layers (energy levels) coincides with the number of the period in which the chemical element is located.

There are completed and incomplete energy levels. A level is considered complete if it contains the maximum possible number of electrons (first level - 2 electrons, second level - 8 electrons, third level - 18 electrons, fourth level - 32 electrons, etc.). An incomplete level contains fewer electrons.
The level furthest from the nucleus of the atom is called external. Electrons located in the outer energy level are called outer (valence) electrons. The number of electrons in the outer energy level coincides with the number of the group in which the chemical element is located. The outer level is considered complete if it contains 8 electrons. Atoms of group 8A elements (inert gases helium, neon, krypton, xenon, radon) have a completed external energy level.

The region of space around the nucleus of an atom in which an electron is most likely to be found is called an electron orbital. Orbitals differ in energy level and shape. Based on their shape, there are s-orbitals (sphere), p-orbitals (three-dimensional figure eight), d-orbitals and f-orbitals. Each energy level has its own set of orbitals: at the first energy level - one s-orbital, at the second energy level - one s- and three p-orbitals, at the third energy level - one s-, three p-, five d-orbitals , at the fourth energy level there are one s-, three p-, five d-orbitals and seven f-orbitals. Each orbital can accommodate a maximum of two electrons.
The distribution of electrons among orbitals is reflected using electronic formulas. For example, for a magnesium atom, the distribution of electrons across energy levels will be as follows: 2e, 8e, 2e. This formula shows that the 12 electrons of a magnesium atom are distributed over three energy levels: the first level is complete and contains 2 electrons, the second level is complete and contains 8 electrons, the third level is incomplete because contains 2 electrons. For a calcium atom, the distribution of electrons across energy levels will be as follows: 2e, 8e, 8e, 2e. This formula shows that 20 electrons of calcium are distributed over four energy levels: the first level is complete and contains 2 electrons, the second level is complete and contains 8 electrons, the third level is incomplete because contains 8 electrons, the fourth level is not completed, because contains 2 electrons.

>> Chemistry: Change in the number of electrons at the external energy level of atoms of chemical elements Each period of D. I. Mendeleev’s system of elements ends with an inert gas.

The most common of the inert (noble) gases in the Earth's atmosphere is argon, which was isolated in pure form earlier than other analogues. What is the reason for the inertness of helium, neon, argon, krypton, xenon and radon? The fact is that atoms of inert gases have eight electrons at the outer levels farthest from the nucleus (helium has two). Eight electrons in the outer level is the limiting number for each element Periodic table, except hydrogen and helium. This is a kind of ideal of energy level strength to which the atoms of all other elements of the Periodic Table strive.

Atoms can achieve this position of electrons in two ways: by donating electrons from the external level (in this case, the external incomplete level disappears, and the penultimate one, which was completed in previous period, becomes external) or accepting electrons that are not enough to reach the coveted eight. Atoms that have fewer electrons on their outer level give them up to atoms that have more electrons on their outer level. It is easy to give one electron, when it is the only one on the outer level, to the atoms of the elements of the main subgroup of group I. It is more difficult to give two electrons, for example, to atoms of elements of the main subgroup of group II. It is even more difficult to give up your three outer electrons to atoms of group III elements. Metal atoms tend to lose electrons from the outer level. And the easier the atoms of a metal element give up their outer electrons, the more to a greater extent It has metallic properties. It is therefore clear that the most typical metals in the Periodic Table are the elements of the main subgroup of group I. From the above we can draw the following conclusion.

Within a period with increasing charge atomic nucleus, and accordingly, with an increase in the number of external electrons, the metallic properties of chemical elements decrease. Nonmetallic properties, characterized by the ease of accepting electrons to the external level, are enhanced.

The most typical nonmetals are the elements of the main subgroup of group VII. The outer level of the atoms of these elements contains seven electrons. Up to eight electrons at the outer level, that is, they only need one electron to reach a stable state of atoms. They easily attach them, exhibiting non-metallic properties.

How do the atoms of the elements of the main subgroup of group IV behave? After all, they have four electrons at the outer level and they are. it would seem that. it makes no difference whether to give or take four electrons. It turned out that the ability of atoms to give or accept electrons is influenced not only by the number of electrons at the external level, but also by another important characteristic of the atom, such as its radius. Within the period, the number of energy levels of atoms of chemical elements does not change, it is the same, but the radius decreases, as the positive charge of the nucleus (the number of protons in it) increases. As a result, the attraction of electrons to the nucleus increases, and the radius of the atom decreases, the atom seems to shrink. Therefore, it becomes increasingly difficult to give away outer electrons and, conversely, increasingly easier to accept the missing up to eight electrons.

Within the same subgroup, the radius of an atom increases with increasing charge of the atomic nucleus, since with a constant number of electrons in the outer level (it is equal to the group number), the number of energy levels increases (it is equal to the period number). Therefore, it becomes increasingly easier for the atom to give up its outer electrons.

Within the same period, metallic properties decrease, and metallic properties increase, since:
a) the charges of atomic nuclei increase;
b) the number of electrons in the outer level increases

Chemistry lesson in 8th grade. "_____"______ 20_____

Change in the number of electrons at the external energy level of atoms of chemical elements.

Target. Consider changes in the properties of atoms of chemical elements in PSHE D.I. Mendeleev.

Educational. Explain the patterns of changes in the properties of elements within small periods and main subgroups; determine the reasons for changes in metallic and non-metallic properties in periods and groups.

Developmental. Develop the ability to compare and find patterns of changes in properties in PSHE D.I. Mendeleev.

Educational. Foster a culture of academic work in the classroom.

During the classes.

1. Org. moment.

2. Repetition of the studied material.

Independent work.

Option 1.

6-10. Indicate the number of energy levels in the atoms of the following elements.

Option 2.

1-5. Indicate the number of neutrons in the nucleus of an atom.

6-10. Indicate the number of electrons in the outer energy level.

11-15. The indicated electronic formula of the atom corresponds to the element.

3. Studying a new topic.

Exercise. Distribute the electrons among the energy levels of the following elements: Mg, S, Ar.

The completed electronic layers have increased robustness and stability. Atoms that have 8 electrons in their outer energy level - inert gases - are stable.

An atom will always be stable if it has 8ē at its external energy level.

How can atoms of these elements reach the 8-electron outer level?

2 ways to complete:

Donate electrons

Accept electrons.

Metals are elements that donate electrons; at their outer energy level they have 1-3 ē.

Nonmetals are elements that accept electrons; their outer energy level is 4-7ē.

Changing properties in PSHE.

Within one period, as the atomic number of an element increases, the metallic properties weaken and the nonmetallic properties increase.

1. The number of electrons at the external energy level increases.

2. The radius of the atom decreases

3. The number of energy levels is constant

In the main subgroups, non-metallic properties decrease, and metallic properties increase.

1. The number of electrons at the external energy level is constant;

2. The number of energy levels increases;

3. The radius of the atom increases.

Thus, francium is the strongest metal, fluorine is the strongest non-metal.

4. Consolidation.

Exercises.

1. Arrange these chemical elements in order of increasing metallic properties:

A) Al, Na, Cl, Si, P

B) Mg, Ba, Ca, Be

B) N, Sb, Bi, As

D) Cs, Li, K, Na, Rb

2. Arrange these chemical elements in order of increasing non-metallic properties:

B) C, Sn, Ge, Si

B) Li, O, N, B, C

D) Br, F, I, Cl

3. Underline the symbols for chemical metals:

A) Cl, Al, S, Na, P, Mg, Ar, Si

B) Sn, Si, Pb, Ge, C

Arrange in order of decreasing metallic properties.

4. Underline the symbols of the chemical elements of non-metals:

A) Li, F, N, Be, O, B, C

B) Bi, As, N, Sb, P

Arrange in order of decreasing nonmetallic properties.

Homework. Page 61- 63. Ex. 4 page 66

Malyugina 14. External and internal energy levels. Completeness of the energy level.

Let us briefly recall what we already know about the structure of the electron shell of atoms:

ü number of energy levels of an atom = number of the period in which the element is located;

ü the maximum capacity of each energy level is calculated using the formula 2n2

ü the outer energy shell cannot contain more than 2 electrons for elements of the 1st period, and more than 8 electrons for elements of other periods

Let's return once again to the analysis of the scheme for filling energy levels in elements of small periods:

Table 1. Filling energy levels

for elements of small periods

Analyze Table 1. Compare the number of electrons in the last energy level and the number of the group in which the chemical element is located.

Have you noticed that the number of electrons in the outer energy level of atoms coincides with the group number, in which the element is found (with the exception of helium)?

!!! This rule is true only for elements main subgroups

Each period of the system ends with an inert element(helium He, neon Ne, argon Ar). The outer energy level of these elements contains the maximum possible number of electrons: helium -2, the remaining elements - 8. These are elements of group VIII of the main subgroup. An energy level similar to the structure of the energy level of an inert gas is called completed. This is a kind of strength limit of the energy level for each element of the Periodic Table. Molecules of simple substances - inert gases - consist of one atom and are characterized by chemical inertness, that is, they practically do not enter into chemical reactions.

For the rest of the PSHE elements, the energy level differs from the energy level of the inert element; such levels are called unfinished. Atoms of these elements strive to complete the outer energy level by giving or receiving electrons.

Questions for self-control

1. What energy level is called external?

2. What energy level is called internal?

3. What energy level is called complete?

4. Elements of which group and subgroup have a completed energy level?

5. What is the number of electrons in the outer energy level of the elements of the main subgroups?

6. How are they similar in structure? electronic level elements of one main subgroup

7. How many electrons in the outer level do elements of a) group IIA contain;

b) IVA group; c) VII A group

View answer

1. Last

2. Any except the last one

3. The one that contains maximum number electrons. And also the outer level, if it contains 8 electrons for the first period - 2 electrons.

4. Group VIIIA elements (inert elements)

5. Number of the group in which the element is located

6. All elements of the main subgroups at the outer energy level contain as many electrons as the group number

7. a) elements of group IIA have 2 electrons in the outer level; b) group IVA elements have 4 electrons; c) Group VII A elements have 7 electrons.

Tasks for independent solution

1. Identify the element based on the following characteristics: a) has 2 electronic levels, on the outer one - 3 electrons; b) has 3 electronic levels, on the outer one - 5 electrons. Write down the distribution of electrons across the energy levels of these atoms.

2. Which two atoms have the same number of filled energy levels?

View answer:

1. a) Let’s establish the “coordinates” of the chemical element: 2 electronic levels – II period; 3 electrons in the outer level – group III A. This is boron 5B. Diagram of electron distribution by energy levels: 2e-, 3e-

b) III period, VA group, element phosphorus 15P. Diagram of electron distribution by energy levels: 2e-, 8e-, 5e-

2. d) sodium and chlorine.

Explanation: a) sodium: +11 )2)8 )1 (filled 2) ←→ hydrogen: +1)1

b) helium: +2 )2 (filled 1) ←→ hydrogen: hydrogen: +1)1

c) helium: +2 )2 (filled 1) ←→ neon: +10 )2)8 (filled 2)

*G) sodium: +11 )2)8 )1 (filled 2) ←→ chlorine: +17 )2)8 )7 (filled 2)

4. Ten. Number of electrons = atomic number

5 c) arsenic and phosphorus. Atoms located in the same subgroup have the same number of electrons.

Explanations:

a) sodium and magnesium (c different groups); b) calcium and zinc (in the same group, but different subgroups); * c) arsenic and phosphorus (in one, main, subgroup) d) oxygen and fluorine (in different groups).

7. d) number of electrons in the outer level

8. b) number of energy levels

9. a) lithium (located in group IA of period II)

10. c) silicon (IVA group, III period)

11. b) boron (2 levels - IIperiod, 3 electrons in the outer level – IIIAgroup)

MBOU "Gymnasium No. 1 of the city of Novopavlovsk"

Chemistry 8th grade

Subject:

"Change in the number of electrons

at the external energy level

atoms of chemical elements"

Teacher: Tatyana Alekseevna Komarova

Novopavlovsk

Date of: ___________

Lesson– 9

Lesson topic: Change in the number of electrons at the external energy

level of atoms of chemical elements.

Lesson objectives:

— form a concept about the metallic and non-metallic properties of elements at the atomic level;

— show the reasons for changes in the properties of elements in periods and groups based on the structure of their atoms;

— give initial ideas about ionic bonds.

Equipment: PSHE, table “Ionic bonding”.

During the classes

Organizing time.

Check of knowledge

Characteristics of chemical elements according to the table (3 people)

Structure of atoms (2 people)

Learning new material

Let's consider the following questions:

1 . Atoms of which chemical elements have complete energy levels?

- these are atoms of inert gases, which are located in the main subgroup of the 8th group.

The completed electronic layers have increased robustness and stability.

Atoms Group VIII (He Ne Ar Kr Xe Rn) contain 8e - at the outer level, which is why they are inert, i.e. . not chemically active, do not interact with other substances, i.e. their atoms have increased stability and stability. That is, all chemical elements (having different electronic structure) tend at chemical interaction get completed outer energy level ,8е - .

Example:

N a Mg F Cl

11 +12 +9 +17

2 8 1 2 8 2 2 7 2 8 7

1s 2 2s 2 p 6 3 s 1 1s 2 2s 2 p 6 3 s 2 1s 2 2s 2 p 5 1s 2 2s 2 p 6 3 s 2 p 5

How do you think atoms of these elements can achieve eight electrons at the outer level?

If (suppose) we close the last level of Na and Mg with our hand, then we get completed levels. Therefore, these electrons must be given up from the external electronic level! Then, when electrons are released, the pre-outer layer of 8e - , becomes external.

And for the elements F and Cl, you should accept 1 missing electron to your energy level, rather than give 7e - . And so, there are 2 ways to achieve a complete energy level:

A) Release of (“extra”) electrons from the outer layer.

B) Acceptance of (“missing”) electrons to the external level.

2. The concept of metallicity and non-metallicity at the atomic level:

Metals are elements whose atoms give up their outer electrons.

Non-metals – These are elements whose atoms accept electrons into the outer energy level.

The easier the Me atom gives up its electrons, the more pronounced its metallic properties.

The easier the HeMe atom accepts the missing electrons to the outer layer, the more strongly expressed its non-metallic properties.

3. Changes in Me and NeMe properties of ch.e. atoms. in periods and groups in PSHE.

In periods:

Example: Na (1e -) Mg (2e -) – write down the structure of the atom.

— Which element do you think has stronger metallic properties, Na or Mg? Which is easier to give 1e - or 2e -? (Of course 1e - , therefore Na has more pronounced metallic properties).

Example: Al (3e -) Si (4e -), etc.

Over the period, the number of electrons in the outer level increases from left to right.

(metallic properties are more pronounced in Al).

Of course, the ability to give up electrons over a period will decrease, i.e. metallic properties will weaken.

Thus, the strongest Mes are located at the beginning of periods.

— How will the ability to add electrons change? (will increase)

Example:

SiCl

14 r +17 r

2 8 4 2 8 7

It is easier to accept 1 missing electron (from Cl) than 4e from Si.

Conclusion:

Non-metallic properties will increase from left to right over the period, and metallic properties will weaken.

Another reason for the enhancement of NeMe properties is a decrease in the radius of the atom with a constant number of levels.

Because within the 1st period, the number of energy levels for atoms does not change, but the number of external electrons e - and the number of protons p - in the nucleus increases. As a result, the attraction of electrons to the nucleus increases (Coulomb's law), and the radius (r) of the atom decreases, the atom seems to shrink.

General conclusion:

Within one period, with an increase in the order number (N) of an element, the metallic properties of the elements weaken, and non-metallic properties increase, because:

- The number e increases - at the external level it is equal to the group number and the number of protons in the nucleus.

— The radius of the atom decreases

— The number of energy levels is constant.

4. Let us consider the vertical dependence of changes in the properties of elements (within the main subgroups) in groups.

Example: VII group main subgroup (halogens)

FCl

9 +17

2 7 2 8 7

1s 2 2s 2 p 5 1s 2 2s 2 p 6 3s 2 p 5

The number e is the same on the external levels of these elements, but the number of energy levels is different,

at F -2e - , and Cl – 3e - /

—Which atom has a larger radius? (—chlorine has 3 energy levels).

The closer the e are located to the nucleus, the more strongly they are attracted to it.

- Which element atom will be easier to add e - F or Cl?

(F – it is easier to add 1 missing electron), because it has a smaller radius, which means the force of attraction of the electron to the nucleus is greater than that of Cl.

Coulomb's law

The force of interaction between two electric charges is inversely proportional to the square

distances between them, i.e. the greater the distance between atoms, the less force

attraction of two opposite charges (in this case, electrons and protons).

F is stronger than Cl ˃Br ˃J, etc.

Conclusion:

In groups (main subgroups), non-metallic properties decrease, and metallic properties increase, because:

1). The number of electrons on the outer level of atoms is the same (and equal to the group number).

2). The number of energy levels in atoms is growing.

3). The radius of the atom increases.

Orally, according to the PSHE table, consider Group I - the main subgroup. Conclude that the strongest metal is Fr francium, and the strongest non-metal is F fluorine.

Ionic bond.

Let's consider what will happen to the atoms of the elements if they reach the octet (i.e. 8e -) at the external level:

Let's write down the formulas of the elements:

Na 0 +11 2e - 8e - 1e - Mg 0 +12 2e - 8e - 2e - F 0 +9 2e - 7e - Cl 0 +17 2e - 8e - 7e -

Na x +11 2e - 8e - 0e - Mg x +12 2e - 8e - 0e - F x +9 2e - 8e - Cl x +17 2e - 8e - 8e -

The top row of formulas contains the same number of protons and electrons, because These are the formulas of neutral atoms (the zero charge is “0” - this is the oxidation state).

Bottom row - different numbers p + and e -, i.e. These are the formulas for charged particles.

Let's calculate the charge of these particles.

Na +1 +11 2e - 8e - 0e - 2+8=10, 11-10 =1, oxidation state +1

F - +9 2е - 8e - 2+8 =10, 9-10 =-1, oxidation state -1

Mg +2 +12 2e — 8e — 0e — 2+8 =10, 12-10 =-2, oxidation state -2

As a result of the addition and loss of electrons, charged particles are obtained, which are called ions.

Me atoms upon recoil e - acquires “+” (positive charge)

Non-Me atoms accepting “foreign” electrons are charged “-” (negative charge)

The chemical bond formed between ions is called ionic.

An ionic bond occurs between strong Me and strong NeMe.

Examples.

a) formation of an ionic bond. Na + Cl -

N a Cl+ —

11 + +17 +11 +17

2 8 1 2 8 7 2 8 2 8 8

1e—

The process of turning atoms into ions:

1 e -

N a 0 + Cl 0 Na + + Cl — Na + Cl —

atom atom ion ion ionic compound

2e -

b) Ca O 2+ 2-

Ca 0 + 2 C l 0 Ca 2+ Cl 2 —

2 e -

Consolidation of knowledge, skills, abilities.

Atoms Me and NeMe

Ions "+" and "-"

Ionic chemical bond

Coefficients and indices.

D/Z§ 9, No. 1, No. 2, p. 58

Lesson summary

Literature:

1. Chemistry 8th grade. textbook for general education

institutions/O.S. Gabrielyan. Bustard 2009

2. Gabrielyan O.S. Teacher's handbook.

Chemistry 8th grade, Bustard, 2003