Task 11.
Write an electron-graphic formula for the 17th element, determine its valence electrons and characterize them using quantum numbers.
Solution:
Electronic configuration nlx
, where n
is the principal quantum number, l
x
n+1
(Klechkovsky's rule
1s>2s>2p>3s>3p>4s>3d>4p>5s>4d>5p>6s>(5d1)>4f>5d>6p>7s>(6d1-2)>5f>6d>7p
Since the number of electrons in an atom of an element is equal to its serial number in the table of D.I. Mendeleev, then for the 17th element - chlorine (Cl - serial number 17) the electronic formula is:
1s 2 2s 2 2p 6 3s 2 3p 5
Valence electrons of chlorine 3s 2 3p 5
- are on the 3s and 3p sublevels There are 7 electrons in the valence orbitals of the Cl atom. Therefore, the element is placed in the seventh group of the periodic system of D.I. Mendeleev.
Electronic formula for the titanium atom
Task 12.
Write an electronic formula for the titanium atom, determine the valence electrons and characterize them using quantum numbers.
Solution:
Electronic formulas display the distribution of electrons in an atom by energy levels, sublevels (atomic orbitals). Electronic configuration denoted by character groups nlx
, where n
is the principal quantum number, l
- orbital quantum number (instead of it indicate the corresponding letter designation - s, p, d, f), x
is the number of electrons in a given sublevel (orbitals). In this case, it should be taken into account that the electron occupies the energy sublevel at which it has the lowest energy - a smaller sum n+1
(Klechkovsky's rule). The sequence of filling energy levels and sublevels is as follows:
1s>2s>2p>3s>3p>4s>3d>4p>5s>4d>5p>6s>(5d1)>4f>5d>6p>7s>(6d1-2)>5f>6d>7p
Since the number of electrons in an atom of an element is equal to its serial number in the table of D.I. Mendeleev, then for the 22nd element -Ti the electronic formula has the form:
1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 2
Valence electrons of titanium 4s 2 3d 2 are on 4s 3d sublevels. In the electronic graphic formulas of atoms, each atomic orbital is denoted by a square ().
An atom is an electrically neutral system consisting of a positively charged nucleus and negatively charged electrons. Electrons are located in the atom, forming energy levels and sublevels.
Electronic formula atom is the distribution of electrons in an atom over energy levels and sublevels in accordance with the principle of least energy (Klechkovsky), Pauli's principle, Hund's rule.
The state of an electron in an atom is described using a quantum mechanical model - an electron cloud, the density of the corresponding sections of which is proportional to the probability of finding an electron. Usually, the electron cloud is understood as the region of the nuclear space, which covers approximately 90% of the electron cloud. This region of space is also called an orbital.
Atomic orbitals form an energy sublevel. Orbitals and sublevels are assigned letter designations. Each sublevel has a certain number of atomic orbitals. If the atomic orbital is depicted as a magnetic-quantum cell, then the atomic orbitals located at sublevels can be represented as follows:
Each atomic orbital can contain no more than two electrons at the same time, differing in spin (Pauli principle). This difference is indicated by arrows ¯. Knowing that on s-sublevel one s-orbital, on R-sublevel three R-orbitals, on d-sublevel five d-orbitals, on f-sublevel seven f- orbitals, you can find the maximum number of electrons in each sublevel and level. Yes, on s-sublevel, starting from the first energy level, 2 electrons; on the R-sublevel, starting from the second energy level, 6 electrons; on the d-sublevel, starting from the third energy level, 10 electrons; on the f-sublevel, starting from the fourth energy level, 14 electrons. Electrons on s-, p-, d-, f- sublevels are named respectively s-, p-, d-, f-electrons.
According to principle of least energy, the successive filling of energy sublevels with electrons occurs in such a way that each electron in an atom occupies a sublevel with the lowest energy corresponding to its strong bond with the nucleus. The change in the energy of sublevels can be represented as a Klechkovsky series or an energy scale:
1s<2s<2p<3s<3p<4s<3d<4p<5s<4d<5p<6s<4f<5d<6p<7s<5f<6d<7p...
According to Hund's rule, each quantum cell (orbital) of the energy sublevel is first filled with single electrons with the same spin, and then with a second electron with the opposite spin. Two electrons with opposite spins in the same atomic orbital are called paired electrons. Single electrons are unpaired.
Example 1 Place 7 electrons on d-sublevel, taking into account the Hund's rule.
Solution.
On the d sublevel - five atomic orbitals. The energy of orbitals that are at the same sublevel is the same. Then d sublevel can be represented as follows: d 
. After filling the atomic orbitals with electrons, taking into account the Hund's rule d-sublevel will look like 
.
Using now the concepts of the principles of least energy and Pauli, we distribute electrons in atoms according to energy levels (Table 1).
Table 1
The distribution of electrons over the energy levels of atoms
Using this scheme, it is possible to explain the formation of the electronic structures of the atoms of the elements of the periodic system, written in the form of electronic formulas. The total number of electrons in an atom is determined by the atomic number of the element.
So, in the atoms of the elements of the first period, one s-orbital of the first energy level (Table 1). Since there are two electrons at this level, there are only two elements in the first period (1 H and 2 He), the electronic formulas of which are as follows: 1 H 1 s 1 and 2 Not 1 s 2 .
In atoms of elements of the second period, the first energy level is completely filled with electrons. will be successively filled with electrons s- and R-sublevels of the second energy level. Sum s- and R-electrons that filled this level is eight, so there are 8 elements in the second period (3 Li ... 10 ne).
In atoms of elements of the third period, the first and second energy levels are completely filled with electrons. will be filled in succession s- and R-sublevels of the third energy level. Sum s- and R-electrons that filled the third energy level is eight. Therefore, in the third period there are 8 elements (11 Na ... 18 Ar).
In the atoms of the elements of the fourth period, the first, second and third are filled 3 s 2 3R 6 energy levels. At the third energy level, the free remains d-sublevel (3 d). The filling of this sublevel with electrons from one to ten begins after it is filled with maximum electrons 4 s-sublevel. Further, the placement of electrons occurs on 4 R-sublevel. Amount 4 s-, 3d- and 4p-electrons is equal to eighteen, which corresponds to 18 elements of the fourth period (19 K ... 36 Kr).
Similarly, the formation of electronic structures of atoms of elements of the fifth period occurs with the only difference that s- and R- sublevels are on the fifth, and d- sublevel on the fourth energy levels. Since the sum is 5 s-, 4d- and 5 R-electrons is eighteen, then in the fifth period there are 18 elements (37 Rb ... 54 Xe).
There are 32 elements in the extra-large sixth period (55 Cs ... 86 Rn). This number corresponds to the sum of electrons by 6 s-, 4f-, 5d- and 6 R-sublevels. The sequence of filling the sublevels with electrons is as follows. First filled with electrons 6 s-sublevel. Then, contrary to the Klechkovsky series, it will be filled with one electron 5 d-sublevel. After that, 4 will be filled to the maximum. f-sublevel. Next, 5 will be filled d- and 6 R-sublevels. The previous energy levels are filled with electrons.
A similar phenomenon is observed during the formation of electronic structures of atoms of elements of the seventh period.
Thus, in order to write the electronic formula of an atom of an element, you need to know the following.
1. Ordinal number of the element in the periodic system of elements D.I. Mendeleev, corresponding to the total number of electrons in an atom.
2. The number of the period, which determines the total number of energy levels in the atom. In this case, the number of the last energy level in the atom corresponds to the number of the period in which the element is located. In atoms of elements of the second and third periods, the filling of the last energy level with electrons occurs in the following sequence: ns 1–2 …np 1–6. In atoms of elements of the third and fourth periods, the sublevels of the last and penultimate energy levels are filled with electrons as follows: ns 1–2 …(n–1)d 1–10 …np 1–6. In the atoms of the elements of the sixth and seventh periods, the sequence of filling sublevels with electrons is as follows: ns 1–2 …(n–1)d 1 …(n-2)f 1–14 …(n–1)d 2–10 …np 1–6 .
3. In the atoms of the elements of the main subgroups, the sum s- and R-electrons at the last energy level is equal to the group number.
4. In atoms of elements of secondary subgroups, the sum d-electrons on the penultimate and s-electrons at the last energy levels is equal to the group number, except for the atoms of the elements of the cobalt, nickel, copper and zinc subgroups.
The placement of electrons in atomic orbitals of the same energy sublevel occurs in accordance with Gund's rule: the total value of the spin of electrons located at the same sublevel should be maximum, i.e. a given sublevel per orbital first accepts one electron with parallel spins, and then a second electron with opposite spin.
Example 2 . Write the electronic formulas of the atoms of elements that have serial numbers 4, 13, 22.
Solution. The element with atomic number 4 is beryllium. Therefore, there are 4 electrons in a beryllium atom. Beryllium is in the second period, in the second group of the main subgroup. The period number corresponds to the number of energy levels, i.e. two. These energy levels must accommodate four electrons. The first energy level has two electrons (1 s 2) and the second also has two electrons (2 s 2) (see Table 1). Thus, the electronic formula has the following form: 4 Be 1 s 2 2s 2. The number of electrons in the last energy level corresponds to the number of the group in which it is located.
The element aluminum corresponds to the element 13 in the periodic system. Aluminum is in the third period, in the third group, in the main subgroup. Therefore, there must be three electrons in the third energy level, which will be placed in this way: 3 s 2 3R 1 (sum s- and R-electrons is equal to the group number). Ten electrons are in the first and second energy levels: 1 s 2 2s 2 2p 6 (see Table 1). In general, the electronic formula of aluminum is as follows: 13 Al 1 s 2 2s 2 2p 6 3s 2 3p 1 .
In the periodic system, the element with the atomic number 22 is titanium. There are twenty-two electrons in a titanium atom. They are placed on four energy levels, since the element is in the fourth period. When placing electrons in sublevels, it must be taken into account that this is an element of the fourth group of the side subgroup. Therefore, at the fourth energy level, s-there are two electrons in the sublevel: 4 s 2. First, second, third levels s- and R- sublevels are completely filled with electrons 1 s 2 2s 2 2p 6 3s 2 3p 6 (see Table 1). The remaining two electrons will be located on d- sublevel of the third energy level: 3 d 2. In general, the electronic formula of titanium is: 22 Ti 1 s 2 2s 2 2p 6 3s 2 3p 6 3d 2 4s 2 .
"Slip" of electrons
When writing electronic formulas, one should take into account the "leakage" of electrons from s- sublevel of the external energy level ns on the d- sublevel of the preexternal level ( n – 1)d. It is assumed that such a state is the most energetically favorable. "Slippage" of an electron occurs in the atoms of some d-elements, for example, 24 Cr, 29 Cu, 42 Mo, 47 Ag, 79 Au, 41 Nb, 44 Ru, 45 Rh, 46 Pd.
Example 3. Write the electronic formula of the chromium atom, taking into account the "breakthrough" of one electron.
Solution. The electronic formula of chromium, according to the principle of minimum energy, should be: 24 Cr 1 s 2 2s 2 2p 6 3s 2 3p 6 3d 4 4s 2. However, in the atom of this element, there is a "slip" of one s-electron from external 4 s- sublevel to sublevel 3 d. Therefore, the arrangement of electrons in a chromium atom is: 24 Cr 1 s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 1 .
In order to learn how to compose electron-graphic formulas, it is significant to realize the theory of the structure of the nuclear nucleus. The nucleus of an atom is made up of protons and neutrons. Electrons are located in electron orbitals around the nucleus of an atom.
You will need
- - a pen;
- - note paper;
- - the periodic system of elements (Mendeleev's table).
Instruction
1. Electrons in an atom occupy vacant orbitals in a sequence called the energy scale: 1s/2s, 2p/3s, 3p/4s, 3d, 4p/5s, 4d, 5p/6s, 4d, 5d, 6p/7s, 5f, 6d, 7p . Two electrons with opposite spins - directions of rotation can be located on one orbital.
2. The design of electron shells is expressed with the support of graphic electronic formulas. Use a matrix to write a formula. One cell can contain one or two electrons with opposite spins. Electrons are represented by arrows. The matrix clearly shows that two electrons can be located in the s-orbital, 6 in the p-orbital, 10 in the d-orbital, and 14 in the f-orbital.
3. Consider the rule for compiling an electronic graphic formula using manganese as an example. Find manganese in the periodic table. Its serial number is 25, which means there are 25 electrons in the atom, this is an element of the fourth period.
4. Write down the serial number and symbol of the element next to the matrix. In accordance with the energy scale, fill in the 1s, 2s, 2p, 3s, 3p, 4s tiers step by step, entering two electrons per cell. You get 2+2+6+2+6+2=20 electrons. These tiers are completely filled.
5. You have five more electrons left and an empty 3d tier. Arrange the electrons in the cells of the d-sublevel, starting from the left. Place the electrons with identical spins in the cells first one by one. If all cells are filled, starting from the left, add a second electron with the opposite spin. Manganese has five d-electrons, located one at a time in the entire cell.
6. Electron graphic formulas clearly show the number of unpaired electrons that determine the valence.
When creating theoretical and factual works in mathematics, physics, chemistry, a student or schoolchild is faced with the need to insert special symbols and difficult formulas. Having the Word application from the Microsoft office suite, it is allowed to type an electronic formula every difficulty.
Instruction
1. Open the newest document in Microsoft Word. Give it a name and save it in the same folder where your work is, so that you don’t look for it in the future.
2. Go to the "Insert" tab. On the right, find the symbol ?, and next to it is the inscription "Formula". Click on the arrow. A window will appear where you can prefer a built-in formula, say a quadratic equation formula.
3. Click on the arrow and a variety of symbols will appear on the top panel that you may need when writing this particular formula. By changing it the way you want it, you can save it. From now on, it will drop out in the list of built-in formulas.
4. If you need to transfer the formula to text, the one that later needs to be placed on the site, then click on the energetic field with it with the right mouse button and select not the highly professional, but the linear method of writing. In particular, the formula of the same quadratic equation in this case will take the form: x=(-b±?(b^2-4ac))/2a.
5. Another option for writing an electronic formula in Word is through the constructor. Hold down the Alt and = keys at the same time. You will immediately have a field for writing a formula, and a constructor will open in the top panel. Here you can prefer all the signs that may be required to write an equation and solve any problem.
6. Some linear notation symbols may be obscure to a reader unfamiliar with computer symbols. In this case, it makes sense to save the most difficult formulas or equations in graphical form. To do this, open the easiest graphic editor Paint: "Start" - "Programs" - "Paint". After that, zoom in on the formula document so that it takes up every screen. This is necessary so that the saved image has the highest resolution. Press PrtScr on your keyboard, go to Paint and press Ctrl+V.
7. Trim off any excess. As a result, you will get a solid image with the necessary formula.
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Note!
Remember that chemistry is a science of exceptions. The atoms of the secondary subgroups of the Periodic system have an electron "breakthrough". For example, in chromium with atomic number 24, one of the electrons from the 4s-tier goes to the d-tier cell. Molybdenum, niobium, etc. have a similar result. In addition, there is a representation of the excited state of the atom, when paired electrons are unpaired and transferred to neighboring orbitals. Therefore, when compiling electronic graphic formulas for the elements of the fifth and subsequent periods of the secondary subgroup, refer to the reference book.
Many metals are common in nature not only in the composition of various rocks or minerals, but also in a free - native form. Examples include gold, silver and copper. However, active metallic elements such as sodium, whose electron-graphic formula we will study, do not occur as a simple substance. The reason is their high reactivity, which leads to the rapid oxidation of the substance by atmospheric oxygen. That is why in the laboratory the metal is stored under a layer of kerosene or industrial oil. The chemical activity of all alkali metal elements can be explained by the structural features of their atoms. Let's consider the electron-graphic formula of sodium and find out how its characteristics affect the physical properties and features of interaction with other substances.
sodium atom
The position of an element in the main subgroup of the first group of the periodic system affects the structure of its electrically neutral particle. This diagram illustrates the arrangement of electrons around the nucleus of an atom and determines the number of energy levels in it:
The number of protons, neutrons, electrons in a sodium atom will be equal to 11, 12, 11, respectively. The proton number and the number of electrons are determined by the element's serial number, and the number of neutral nuclear particles will be equal to the difference between the nucleon number (atomic mass) and the proton number (serial number ). To record the distribution of negatively charged particles in an atom, you can use the following electronic formula: 1s 2 2s 2 2p 6 3s 1.
The relationship between the structure of the atom and the properties of matter
The properties of sodium as an alkali metal can be explained by the fact that it belongs to the s-elements, its valency is 1, and the oxidation state is +1. One unpaired electron on the third, last, layer determines its reduction characteristics. In reactions with other atoms, sodium always donates its own negative particle to more electronegative elements. For example, being oxidized by atmospheric oxygen, Na atoms become positively charged particles - cations that are part of the basic oxide Na 2 O molecule. This reaction has the following form:
4Na + O 2 \u003d 2Na 2 O.
Physical properties
The electron-graphic formula of sodium and its crystal lattice determine such element parameters as the state of aggregation, melting and boiling points, as well as the ability to conduct heat and electric current. Sodium is a light (density 0.97 g/cm3) and very soft silvery metal. The presence of freely moving electrons in the crystal lattice causes high thermal and electrical conductivity. It occurs naturally in minerals such as common salt NaCl and sylvinite NaCl × KCl. Sodium is very common not only in inanimate nature, for example, in the composition of rock salt deposits or sea water of the seas and oceans. He, along with chlorine, sulfur, calcium, phosphorus and other elements, is among the ten most important organogenic chemical elements that form living biological systems.
Features of chemical properties
The electron-graphic formula of sodium clearly shows that the only s-electron rotating on the last, third energy layer of the Na atom is weakly bound to the positively charged nucleus. It easily leaves the limits of the atom, so sodium in reactions with oxygen, water, hydrogen and nitrogen behaves like a strong reducing agent. Here are examples of reaction equations typical for alkali metals:
2Na + H 2 \u003d 2NaH;
6Na + N 2 \u003d 2Na 3 N;
2Na + 2H 2 O \u003d 2NaOH + H 2.
The reaction with water ends with the formation of chemically aggressive compounds - alkalis. Sodium hydroxide, also called, exhibits the properties of active bases and in the solid state has found application as a gas desiccant. Sodium metal is produced in industry by electrolysis of a salt melt - sodium chloride or the corresponding hydroxide, while a layer of sodium metal is formed on the cathode.
In our article, we examined the electronic graphic formula of sodium, and also studied its properties and production in industry.
A record that reflects the distribution of electrons in an atom of a chemical element over energy levels and sublevels is called electronic configuration this atom. In the ground (unexcited) state of an atom, all electrons satisfy the principle of minimum energy. This means that the sublevels are filled first, for which:
1) The main quantum number n is minimal;
2) Inside the level, the s-sublevel is first filled, then p- and only then d- (l is minimal);
3) Filling occurs so that (n + l) is minimal (Klechkovsky's rule);
4) Within one sublevel, electrons are located in such a way that their total spin is maximum, i.e. contained the largest number of unpaired electrons (Hund's rule).
5) When filling electronic atomic orbitals, the Pauli principle is fulfilled. Its consequence is that the energy level with number n can have no more than 2n 2 electrons located on n 2 sublevels.
In the record of electronic formulas (or configurations) reflecting this sequence, the first digit is equal to n, the letter after it corresponds to l, and the upper right index is equal to the number of electrons in this state.
For example, cesium (Cs) is in the 6th period, its 55 electrons (serial number 55) are distributed over 6 energy levels and their sublevels, following the sequence of filling the orbitals with electrons, we get: 55 Cs 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 4 s 2 4 p 6 4 d 10 5 s 2 5 p 6 5 d 10 6 s 1
In turn, the electronic formula of lithium - 1 s 2 2 s 1 , carbon - 1 s 2 2 s 2 2 p 2 , chlorine - 1 s 2 2 s 2 2 p 6 3 s 2 3 p 5 .
The population of electron shells can be represented as quantum cells (squares or horizontal lines). Unlike electronic formulas, not two, but all four quantum numbers are used here. It can be seen that the energy of electrons in multielectron atoms is defined as the quantum number n, and l; electrons differ in value ml, and only spins are different for paired electrons. Free cells in our example mean free p-orbitals that can occupy electrons when an atom is excited (Fig. 8).
Rice. 8. Graphic representation of the electronic formula of boron.
Investigating the change in the chemical properties of elements depending on the value of their relative atomic mass (atomic weight), D. I. Mendeleev in 1869 discovered law of periodicity these properties: The properties of the elements, and therefore the properties of the simple and complex bodies they form, are in a periodic dependence on the atomic weights of the elements". Since the chemical properties are determined by the structure of the electron shells of the atom, periodic system of Mendeleev - this is a natural classification of elements according to the electronic structures of their atoms (Appendix 4). The simplest basis for such a classification is the number of electrons in a neutral atom, which is equal to the charge of the nucleus. But when a chemical bond is formed, electrons can be redistributed between atoms, and the charge of the nucleus remains unchanged, so the modern formulation of the periodic law reads: "The properties of the elements are in a periodic dependence on the charges of the nuclei of their atoms".
This circumstance is reflected in the periodic system in the form of horizontal and vertical rows - periods and groups.
Period - a horizontal row with the same number of electronic levels, the period number coincides with the value of the main quantum number n outer level (layer); There are seven such periods in the periodic system. The second and subsequent periods begin with an alkaline element ( ns 1) and ends with a noble gas ( ns 2 np 6).
Vertically, the periodic table is divided into eight groups, which are divided into main - A , consisting of s- and p-elements, and side - B-subgroups containing d-elements. Subgroup III B, except d-elements, contains 14 4 f- and 5 f-elements (families 4 f-lanthanides and 5 f-actinides). The main subgroups contain the same number of electrons on the outer electron layer, which is equal to the group number. In the main subgroups, valence electrons (electrons capable of forming chemical bonds) are located on s- and p-orbitals of the outer energy level, in side - on s-orbitals of the outer and d-orbitals of the preexternal layer. For f-elements are valence ( n – 2)f- (n – 1)d- and ns-electrons. The similarity of elements within each group is the most important pattern in the periodic table. In addition, it should be noted that diagonal similarity for pairs of elements Li and Mg, Be and Al, B and Si, etc. This pattern is due to the tendency to change properties vertically (in groups) and their change horizontally (in periods).
The structure of the electron shell of the atoms of an element changes periodically with an increase in the ordinal number of the element, on the one hand, and, on the other hand, the properties are determined by the structure of the electron shell and, therefore, are in a periodic dependence on the charge of the atomic nucleus.
Periodicity of atomic characteristics
The periodic nature of the change in the chemical properties of the atoms of elements depends on changes in the radius of the atom and ion.
The position of the main maximum density of the outer electron shells is taken as the radius of a free atom. This so-called orbital radius . If we consider the relative values of atomic radii, then it is easy to detect the periodicity of their dependence on the number of the element.
In periods orbital atomic radii as nuclear charge increases Z generally decrease monotonically due to an increase in the degree of interaction of external electrons with the nucleus. In subgroups the radii mainly increase due to the increase in the number of electron shells.
At s- and p-elements, the change in radii, both in periods and in subgroups, is more pronounced than in d- and f-elements, since d- and f electrons are internal. Reducing the radii d- and f-elements in periods is called d - andf - compression. Consequence f-compression is that the atomic radii of the electronic counterparts d-elements of the fifth and sixth periods are almost the same.
These elements, due to the proximity of their properties, are called twin elements.
The formation of ions leads to a change in ionic radii compared to atomic ones. In this case, the cation radii are always smaller, and the anion radii are always larger than the corresponding atomic radii.
The properties of atoms are considered as the ability to give or receive electrons due to the desire of atoms to acquire a stable electronic configuration, similar to inert gases. Metallic properties are considered as the ability of element atoms to donate electrons and exhibit reducing properties, while non-metallic properties are considered to accept electrons and exhibit oxidizing properties.
Ionization energy atom I is the energy required to convert a neutral atom into a positively charged ion. Its value depends on the value of the charge of the nucleus, on the radius of the atom and on the interaction between electrons. The ionization energy is expressed in kJ∙mol –1 or eV. For chemical research, the most important ionization potential the first order is the energy expended on the complete removal of a weakly bound electron from an atom in an unexcited state.
E o - e- \u003d E +, I 1 – first ionization potential;
E + - e- \u003d E 2+, I 2 - the second ionization potential, etc. I 1 < I 2 < I 3 < I 4 ...
The ionization energy determines the nature and strength of the chemical bond, and restorative properties of elements (Table 28).