Electronic formulas of atoms of chemical elements of the 3rd period. Electronic formulas of atoms

Problem 56.
Write an electron-graphical formula for the elements of the 4th period, determine their 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 groups of characters nl x , Where n – principal quantum number, l – orbital quantum number (instead indicate the corresponding letter designation – s, p, d, f ), x – the number of electrons in a given sublevel (orbital). It should be taken into account that the electron occupies the energy sublevel at which it has the lowest energy - a smaller amount n+1 (Klechkovsky's rule ). The sequence of filling energy levels and sublevels is as follows:

1s 2s 2р 3s 3р 4s 3d 4р 5s 4d 5р 6s (5d1) 4f 5d 6р 7s (6d1-2) 5f 6d 7р

a) Element No. 19
Since the number of electrons in an atom of a particular element is equal to its serial number in the D.I. table. Mendeleev, then for the 19th element - potassium (K - atomic number 19) the electronic formula is:

Valence electron potassium 4s 1 - are on 4s -sublevel There is 1 electron in the valence orbital of the K atom. Therefore, the element is placed in the first group of D.I. Mendeleev’s periodic table.

b) Element No. 20
For element No. 20 - calcium (Ca - atomic number 20) the electronic formula is:

Valence electrons calcium 4s 2 - are on 4s -sublevel The valence orbital of the Ca atom contains 2 electrons. Therefore, the element is placed in the second group of D.I. Mendeleev’s periodic table.

c) Element No. 21
For element No. 21 - scandium (Ca - atomic number 21) the electronic formula is:

1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 1

Valence electrons scandia 4s 2 3d 1 - are on 4s - And 3d -sublevels. There are 3 electrons in the valence orbitals of the Sc atom. Therefore, the element is placed in the third group of D.I. Mendeleev’s periodic table.

d) Element No. 22
For element No. 22 - titanium (Ti – atomic number 22) the electronic formula is:

1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 2

Scandium valence electrons 4s 2 3d 2 - are on 4s- And 3d- sublevels. There are 4 electrons in the valence orbitals of a Ti atom. Therefore, the element is placed in the fourth group of D.I. Mendeleev’s periodic table.

e) Element No. 23
For element No. 23 - vanadium (V – atomic number 23) the electronic formula is:

1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 3

Scandium valence electrons 4s 2 3d 3 - are on 4s- And 3d- sublevels. There are 5 electrons in the valence orbitals of the V atom. Therefore, the element is placed in the fifth group of D.I. Mendeleev’s periodic table.

f) Element No. 24
For the element chromium (Cr – atomic number 24) the electronic formula is:

1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5

Valence electrons chromium 4s 1 3d 5 - are on 4s- And 3- sublevels. There are 6 electrons in the valence orbitals of the Cr atom. Therefore, the element is placed in the sixth group of D.I. Mendeleev’s periodic table.
In the chromium atom, one electron moves from the 4s sublevel to the 3d sublevel, and in this case the chromium atom acquires a more stable state 4s 1 3d 5 than 4s 2 3d 4. This is explained by the fact that it is energetically more favorable for the chromium atom when the 3d sublevel contains not 4 but 5 electrons - all cells are filled with one electron. Thus, the valence electron configuration 4s 1 3d 5 is energetically more favorable for the chromium atom rather than 4s 2 3d 4 .

g) Element No. 25 - manganese (Mn – atomic number 25) electronic formula is:

1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5

Valence electrons of manganese 4s 2 3d 5 - are on 4s- And 3d- sublevels. There are 7 electrons in the valence orbitals of the Mn atom. Therefore, the element is placed in the seventh group of D.I. Mendeleev’s periodic table.

h) Element No. 26 - iron (Fe – atomic number 26) electronic formula is:

1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6

Valence electrons gland 4s 2 3d 6 - are on 4s- And 3d -sublevels. There are 8 electrons in the valence orbitals of the Fe atom. Therefore, the element is placed in the eighth group of D.I. Mendeleev’s periodic table.

j) Element No. 27 - sobalt (Co – atomic number 27), the electronic formula is:

1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 7

Valence electrons sobalta 4s 2 3d 7 - are on 4s- And 3d- sublevels. There are 9 electrons in the valence orbitals of the Co atom. Therefore, the element is placed in the ninth group of D.I. Mendeleev’s periodic table.

k) Element No. 28 - nickel (Ni – serial No. 28) electronic formula is:

1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 8

Nickel valence electrons 4s 2 3d 8 - are on 4s- And 3d- sublevels. There are 10 electrons in the valence orbitals of the Ni atom. Therefore, the element is placed in the tenth group of D.I. Mendeleev’s periodic table.

m) Element No. 29 - copper (Cu – serial No. 29) electronic formula is:

1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 10

Valence electrons copper 4s 1 3d 10 - are on 4s- And 3d- sublevels. There are 11 electrons in the valence orbitals of a Cu atom. Therefore, the element is placed in the eleventh group of D.I. Mendeleev’s periodic table.
The copper atom exhibits a breakthrough ( "failure"): one electron from the 4s sublevel goes to the 3d sublevel. This is explained by the fact that the state of the atom is considered more energetically favorable if the d-sublevel contains not 9, but 10 electrons. Because it is energetically more favorable for a copper atom when all five d-cells on the 3d sublevel are filled, but not when four d-cells are filled, and there is only one electron on the fifth. To fill the fifth d-cell of the 3d sublevel, one electron of the 4s sublevel moves to the 3d sublevel, as if " fails". Thus, the valence electron configuration 4s 1 3d 10 is energetically more favorable for the copper atom rather than 4s 2 3d 9.

m) Element No. 30 - zinc (Zn – atomic number 30) electronic formula is:

1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10

Valence electrons of zinc 4s 2 3d 10 - are on 4s- And 3d- sublevels. There are 12 electrons in the valence orbitals of the Zn atom. Therefore, the element is placed in the twelfth group of D.I. Mendeleev’s periodic table.

o) Element No. 31 - gallium (Ga – atomic number 31) electronic formula is:

1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4р 1

Valence electrons of gallium 4s 2 3d 10 4р 1 - are located on 4s-, 3d- And 4p- sublevels. There are 13 electrons in the valence orbitals of a Ga atom. Therefore, the element is placed in the thirteenth group of D.I. Mendeleev’s periodic table.

n) Element No. 32 - germanium (Ge – atomic number 32) electronic formula is:

1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4р 2

Valence electrons of germanium 4s 2 3d 10 4р 2 - are on 4s-, 3d- And 4p- sublevels. There are 14 electrons in the valence orbitals of the Ge atom. Therefore, the element is placed in the fourteenth group of D.I. Mendeleev’s periodic table.

p) Element No. 33 - arsenic (As – atomic number 33) electronic formula is:

1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 3

Valence electrons arsenic 4s 2 3d 10 4р 3 - are on 4s-, 3d- And 4p- sublevels. There are 15 electrons in the valence orbitals of the As atom. Therefore, the element is placed in the fifteenth group of D.I. Mendeleev’s periodic table.

c) Element No. 34 - selenium (Se – atomic number 34) electronic formula is:

1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4р 4

Valence electrons Selena 4s 2 3d 10 4р 4 - are on 4s-, 3d- And 4p- sublevels. There are 16 electrons in the valence orbitals of the Se atom. Therefore, the element is placed in the sixteenth group of D.I. Mendeleev’s periodic table.

c) Element No. 35 - bromine (Br – atomic number 35) electronic formula is:

1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4р 5

Valence electrons bromine 4s 2 3d 10 4 r 5 - are on 4s-, 3d- And 4p -sublevels. There are 17 electrons in the valence orbitals of the Br atom. Therefore, the element is placed in the seventeenth group of D.I. Mendeleev’s periodic table.

r) Element No. 36 - krypton (Kr – atomic number 36) electronic formula is:

1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4р 6

Valence electrons krypton 4s 2 3d 10 4p 6 - are on 4s-, 3d- And 4p- sublevels. There are 18 electrons in the valence orbitals of the Kr atom. Therefore, the element is placed in the eighteenth group of D.I. Mendeleev’s periodic table.

Let's find out how to create the electronic formula of a chemical element. This question is important and relevant, as it gives an idea not only of the structure, but also of the expected physical and chemical properties of the atom in question.

Compilation rules

In order to compose a graphical and electronic formula of a chemical element, it is necessary to have an understanding of the theory of atomic structure. To begin with, there are two main components of an atom: the nucleus and the negative electrons. The nucleus includes neutrons, which have no charge, as well as protons, which have a positive charge.

Discussing how to compose and determine the electronic formula of a chemical element, we note that to find the number of protons in the nucleus, the Mendeleev periodic system will be required.

The number of an element corresponds in order to the number of protons found in its nucleus. The number of the period in which the atom is located characterizes the number of energy layers on which electrons are located.

To determine the number of neutrons devoid of electrical charge, it is necessary to subtract its serial number (number of protons) from the relative mass of an element’s atom.

Instructions

In order to understand how to compose the electronic formula of a chemical element, consider the rule for filling sublevels with negative particles, formulated by Klechkovsky.

Depending on how much free energy the free orbitals have, a series is compiled that characterizes the sequence of filling the levels with electrons.

Each orbital contains only two electrons, which are arranged in antiparallel spins.

In order to express the structure of electronic shells, graphic formulas are used. What do the electronic formulas of atoms of chemical elements look like? How to create graphic options? These questions are included in the school chemistry course, so we will dwell on them in more detail.

There is a certain matrix (basis) that is used when drawing up graphic formulas. The s-orbital is characterized by only one quantum cell, in which two electrons are located opposite each other. They are indicated graphically by arrows. For the p-orbital, three cells are depicted, each also containing two electrons, the d orbital contains ten electrons, and the f orbital is filled with fourteen electrons.

Examples of compiling electronic formulas

Let's continue the conversation about how to compose the electronic formula of a chemical element. For example, you need to create a graphical and electronic formula for the element manganese. First, let's determine the position of this element in the periodic table. It has atomic number 25, therefore, there are 25 electrons in the atom. Manganese is a fourth period element and therefore has four energy levels.

How to write the electronic formula of a chemical element? We write down the sign of the element, as well as its serial number. Using Klechkovsky’s rule, we distribute electrons among energy levels and sublevels. We place them sequentially on the first, second, and third levels, placing two electrons in each cell.

Next, we sum them up, getting 20 pieces. Three levels are completely filled with electrons, and only five electrons remain on the fourth. Considering that each type of orbital has its own energy reserve, we distribute the remaining electrons into the 4s and 3d sublevels. As a result, the finished electronic graphic formula for the manganese atom has the following form:

1s2 / 2s2, 2p6 / 3s2, 3p6 / 4s2, 3d3

Practical significance

Using electron graphic formulas, you can clearly see the number of free (unpaired) electrons that determine the valence of a given chemical element.

We offer a generalized algorithm of actions with which you can create electron graphic formulas for any atoms located in the periodic table.

First of all, it is necessary to determine the number of electrons using the periodic table. The period number indicates the number of energy levels.

Belonging to certain group is related to the number of electrons located in the outer energy level. The levels are divided into sublevels and filled in taking into account the Klechkovsky rule.

Conclusion

In order to determine the valence possibilities of any chemical element located in the periodic table, it is necessary to compile an electronic graphic formula of its atom. The algorithm given above will allow you to cope with the task, determine possible chemical and physical properties atom.

In order to learn how to compose electron graphic formulas, it is important to understand the theory of the structure of the nuclear nucleus. The nucleus of an atom is made up of protons and neutrons. There are electrons around the nucleus of an atom in electron orbitals.

You will need

• - pen;
• – paper for notes;
• – periodic table of elements (periodic table).

Instructions

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 . One orbital can contain two electrons with opposite spins - directions of rotation.

2. The design of electronic shells is expressed using graphical electronic formulas. Use a matrix to write the formula. One or two electrons with opposite spins can be located in one cell. Electrons are represented by arrows. The matrix clearly shows that two electrons can be located in the s orbital, 6 electrons in the p orbital, 10 in the d orbital, and -14 in the f orbital.

3. Consider the rule for drawing up an electronic graphic formula using manganese as an example. Find manganese in the periodic table. Its atomic number is 25, which means there are 25 electrons in the atom, it 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 the 1s, 2s, 2p, 3s, 3p, 4s tiers step by step, writing two electrons per cell. You get 2+2+6+2+6+2=20 electrons. These tiers are completely filled.

5. You still have five electrons left and an unfilled 3d tier. Arrange the electrons in the d-sublevel cells, starting from the left. Place electrons with identical spins in cells one at a time. If all the cells are filled, starting from the left, add a second electron with the opposite spin. Manganese has five d-electrons, distributed one throughout the cell.

6. Electron graphic formulas clearly show the number of unpaired electrons that determine valence.

When creating theoretical and actual work 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, you can type an email formula every difficulty.

Instructions

1. Open newest document in Microsoft Word. Give it a name and save it in the same folder where you have your work, so you don’t have to look for it in the future.

2. Go to the "Insert" tab. On the right you will find the symbol ?, and next to it 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 the top bar will display a variety of symbols that you may need when writing this specific formula. By changing it the way you need, you can save it. From now on, it will appear in the list of built-in formulas.

4. If you need to transfer the formula into text that you later need to place on the site, then right-click on the active field with it and select not the highly professional, but the linear writing method. 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 choose all the signs that may be required to write an equation and solve any problem.

6. Some linear notation symbols may be unclear to a reader unfamiliar with computer symbology. 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, scale up the document with the formula 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 high-quality image with the necessary formula.

Video on the topic

Pay attention!
Remember that chemistry is a science of exceptions. In atoms of side subgroups of the Periodic Table, electron “leakage” occurs. Let's say, in chromium with serial number 24, one of the electrons from the 4s-tier goes to the d-tier cell. A similar result is found for molybdenum, niobium, etc. In addition, there is a representation of the excited state of the atom, when paired electrons are paired and transferred to neighboring orbitals. Consequently, when compiling electronic graphic formulas for the elements of the fifth and subsequent periods of the secondary subgroup, check the reference book.

The electronic structure of an atom can be shown by an electronic formula and an electron graphic diagram. In electronic formulas, energy levels and sublevels are written sequentially in the order in which they are filled and the total number of electrons in the sublevel. In this case, the state of an individual electron, in particular its magnetic and spin quantum numbers, is not reflected in the electronic formula. In electronic graphic circuits, each electron is “visible” completely, i.e. it can be characterized by all four quantum numbers. Electron graphic diagrams are usually given for external electrons.

Example 1. Write the electronic formula of fluorine, express the state of the outer electrons with an electronic graphic diagram. How many unpaired electrons are there in an atom of this element?

Solution. The atomic number of fluorine is nine, therefore, its atom has nine electrons. In accordance with the principle of least energy, using Fig. 7 and taking into account the consequences of the Pauli principle, we write the electronic formula of fluorine: 1s 2 2s 2 2p 5. For the outer electrons (second energy level), we draw up an electron graphic diagram (Fig. 8), from which it follows that the fluorine atom has one unpaired electron.

Rice. 8. Electron graphic diagram of valence electrons of a fluorine atom

Example 2. Make electronic graphic diagrams of possible states of the nitrogen atom. Which of them reflect a normal state, and which ones reflect an excited state?

Solution. The electronic formula of nitrogen is 1s 2 s 2 2p 3, the formula of outer electrons is: 2s 2 2p 3. Sublevel 2p is incomplete because the number of electrons on it is less than six. Possible options The distributions of three electrons at the 2p sublevel are shown in Fig. 9.

Rice. 9. Electron graphic diagrams of possible states of the 2p sublevel in the nitrogen atom.

Maximum (by absolute value) the spin value (3 / 2) corresponds to states 1 and 2, therefore, they are ground, and the rest are excited.

Example 3. Determine the quantum numbers that determine the state of the last electron in the vanadium atom?

Solution. The atomic number of vanadium is Z = 23, therefore, the complete electronic formula of the element is: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 3. The electronic graphic diagram of external electrons (4s 2 3d 3) is as follows (Fig. 10):

Rice. 10. Electron graphic diagram of the valence electrons of the vanadium atom

Principal quantum number of the last electron n = 3 (third energy level), orbital l= 2 (sublevel d). The magnetic quantum number for each of the three d-electrons is different: for the first it is –2, for the second –1, for the third – 0. The spin quantum number for all three electrons is the same: m s = + 1 / 2. Thus, the state of the last electron in a vanadium atom is characterized by quantum numbers: n = 3; l= 2; m = 0; m s = + 1 / 2 .

7. Paired and unpaired electrons

Electrons that fill orbitals in pairs are called paired, and single electrons are called unpaired. Unpaired electrons provide chemical bonds between an atom and other atoms. The presence of unpaired electrons is established experimentally by studying magnetic properties. Substances with unpaired electrons paramagnetic(they are drawn into a magnetic field due to the interaction of electron spins, like elementary magnets, with an external magnetic field). Substances that have only paired electrons diamagnetic(external magnetic field does not affect them). Unpaired electrons are found only at the outer energy level of the atom and their number can be determined from its electron-graphic diagram.

Example 4. Determine the number of unpaired electrons in a sulfur atom.

Solution. The atomic number of sulfur is Z = 16, therefore the full electronic formula of the element is: 1s 2 2s 2 2p 6 3s 2 3p 4. The electronic graphic diagram of external electrons is as follows (Fig. 11).

Rice. 11. Electron graphic diagram of valence electrons of a sulfur atom

From the electron graphic diagram it follows that the sulfur atom has two unpaired electrons.

According to the ideas of Heitler and London, the valence of elements is determined by the number of unpaired electrons. Let's consider the electronic graphic formulas of some elements, in which the orbitals are represented in the form of square cells, and the electron in the form of arrows + ½; -1/2.

From these formulas it follows that in the normal (unpaired) state, carbon has valency II, Sc – I. Atoms can go into an excited state, in which the lower lying sublevels can go from the lower lying sublevels to the higher lying empty sublevels (within one sublevel).

6. Periodic law and periodic system D.I. Mendeleev Structure of the periodic system (period, group, subgroup). The meaning of the periodic law and the periodic system.

Periodic law D.I. Mendeleev:Properties simple tel, A Also forms And properties connectopinion elements are V periodic dependencies from quantities atomic scales elements.(The properties of elements are periodically dependent on the charge of the atoms of their nuclei).

Periodic table of elements. Series of elements within which properties change sequentially, such as the series of eight elements from lithium to neon or from sodium to argon, Mendeleev called periods. If we write these two periods one below the other so that sodium is under lithium and argon is under neon, we get the following arrangement of elements:

With this arrangement, the vertical columns contain elements that are similar in their properties and have the same valency, for example, lithium and sodium, beryllium and magnesium, etc.

Having divided all the elements into periods and placing one period under another so that elements similar in properties and type of compounds formed were located under each other, Mendeleev compiled a table that he called the periodic system of elements by groups and series.

The meaning of the periodic systemWe. The periodic table of elements had a great influence on the subsequent development of chemistry. Not only was it the first natural classification of chemical elements, showing that they form a harmonious system and are in close connection with each other, but it was also a powerful tool for further research.

7. Periodic changes in the properties of chemical elements. Atomic and ionic radii. Ionization energy. Electron affinity. Electronegativity.

The dependence of atomic radii on the charge of the nucleus of an atom Z is periodic. Within one period, as Z increases, there is a tendency for the size of the atom to decrease, which is especially clearly observed in short periods

With the beginning of the construction of a new electronic layer, more distant from the nucleus, i.e., during the transition to the next period, atomic radii increase (compare, for example, the radii of fluorine and sodium atoms). As a result, within a subgroup, with increasing nuclear charge, the sizes of atoms increase.

The loss of electron atoms leads to a decrease in its effective size, and the addition of excess electrons leads to an increase. Therefore, the radius of a positively charged ion (cation) is always smaller, and the radius of a negatively charged non (anion) is always greater than the radius of the corresponding electrically neutral atom.

Within one subgroup, the radii of ions of the same charge increase with increasing nuclear charge. This pattern is explained by an increase in the number of electronic layers and the growing distance of outer electrons from the nucleus.

The most characteristic chemical property of metals is the ability of their atoms to easily give up external electrons and transform into positively charged ions, while non-metals, on the contrary, are characterized by the ability to add electrons to form negative ions. To remove an electron from an atom and transform the latter into a positive ion, it is necessary to expend some energy, called ionization energy.

Ionization energy can be determined by bombarding atoms with electrons accelerated in an electric field. The lowest field voltage at which the electron speed becomes sufficient to ionize atoms is called the ionization potential of the atoms of a given element and is expressed in volts.

With the expenditure of sufficient energy, two, three or more electrons can be removed from an atom. Therefore, they speak of the first ionization potential (the energy of the removal of the first electron from the atom) and the second ionization potential (the energy of the removal of the second electron)

As noted above, atoms can not only donate, but also gain electrons. The energy released when an electron attaches to a free atom is called the atom's electron affinity. Electron affinity, like ionization energy, is usually expressed in electron volts. Thus, the electron affinity of the hydrogen atom is 0.75 eV, oxygen - 1.47 eV, fluorine - 3.52 eV.

The electron affinities of metal atoms are typically close to zero or negative; It follows from this that for atoms of most metals the addition of electrons is energetically unfavorable. The electron affinity of nonmetal atoms is always positive and the greater, the closer the nonmetal is located to the noble gas in the periodic table; this indicates an increase in non-metallic properties as the end of the period approaches.