How the electronic formula of an item is spelled. Electronic formulas of chemical elements. Informative value of electronic formulas

DEFINITION

Electronic formula(configuration) of an atom of a chemical element shows the arrangement of electrons on electron shells (levels and sublevels) in an atom or molecule.

Most often, electronic formulas are written for atoms in the ground or excited state and for ions.

There are several rules that must be taken into account when drawing up the electronic formula of an atom of a chemical element. This is Pauli's principle, Klechkovsky's rules or Hund's rule.

When drawing up an electronic formula, it should be borne in mind that the period number of a chemical element determines the number of energy levels (shells) in an atom, and its ordinal number determines the number of electrons.

According to the Klechkovsky rule, the filling of the energy levels occurs in the increasing order of the sum of the principal and orbital quantum numbers (n + l), and for equal values ​​of this sum, in the increasing order of n:

1s< 2s < 2p < 3s < 3p < 4s ≈ 3d < 4p < 5s ≈ 4d < 5p < 6s ≈ 5d ≈ 4f < 6p и т.д.

Thus, the value n + l = 5 corresponds to the energy sublevels 3d (n = 3, l = 2), 4d (n = 4, l = 1), and 5s (n = 5, l = 0). The first of these sublevels is filled with the one with the lower value of the principal quantum number.

The behavior of electrons in atoms obeys the exclusion principle formulated by the Swiss scientist W. Pauli: there cannot be two electrons in an atom that have all four quantum numbers the same. According to Pauli principle, in one orbital, characterized by certain values ​​of the three quantum numbers (principal, orbital and magnetic), there can be only two electrons that differ in the value of the spin quantum number. Pauli's principle implies consequence: the maximum possible number of electrons at each energy level is equal to twice the square of the principal quantum number.

Electronic formula of the atom

The electronic formula of the atom is depicted as follows: each energy level corresponds to a certain principal quantum number n, denoted Arabic numerals; each number is followed by a letter corresponding to the energy sublevel and denoting the orbital quantum number. The superscript next to the letter indicates the number of electrons in the sublevel. For example, the electronic formula of the sodium atom has next view:

11 N 1s 2 2s 2 2p 6 3s 1.

When filling the energy sublevels with electrons, it is also necessary to observe Hund's rule: in this sublevel, electrons tend to occupy energy states in such a way that the total spin is maximum (this is most clearly reflected when drawing up electronic-graphic formulas).

Examples of problem solving

EXAMPLE 1

When graphically depicting the formulas of substances, the sequence of arrangement of atoms in a molecule is indicated using the so-called valence strokes (the term "valence stroke" was proposed in 1858 by A. Cooper to denote the chemical forces of adhesion of atoms), otherwise called valence trait (each valence trait, or valence prime, are equivalent to one pair of electrons in covalent compounds or one electron participating in the formation of an ionic bond). The graphic representation of formulas is often mistaken for structural formulas that are acceptable only for compounds with a covalent bond and show the mutual arrangement of atoms in a molecule.

Let's show this with examples. Mentally, we preliminarily "break" a sheet of paper into several columns and perform actions according to algorithms for a graphical representation of the formulas of oxides, bases, acids, salts in the following order.

Graphical representation of oxide formulas (for example, A l 2 O 3 )

III II

1. Determine the valence of the atoms of the elements in A l 2 O 3

2. We write down the chemical signs of metal atoms in the first place (first column). If there are more than one metal atoms, then we write in one column and denote the valence (the number of bonds between atoms) with valence primes

H. The second place (column), also in one column, is occupied by the chemical signs of oxygen atoms, and two valence primes must fit to each oxygen atom, since oxygen is divalent

lll ll l

Graphical representation of base formulas(for example F e (OH) 3)

1. Determine the valence of atoms of elements Fe (OH) 3

2. In the first place (first column) we write the chemical signs of metal atoms, we designate their valence F e

H. The second place (column) is occupied by the chemical signs of oxygen atoms, which are attached by one bond to the metal atom, the second bond is still "free"

4. The third place (column) is taken by the chemical signs of hydrogen atoms joining to the "free" valence of oxygen atoms

Graphical representation of acid formulas (for example, H 2 SO 4 )

lVlll

1. Determine the valence of the atoms of the elements Н 2 SO 4 .

2. In the first place (first column) we write the chemical signs of hydrogen atoms in one column with the designation of the valence

H—

H—

H. The second place (column) is occupied by oxygen atoms, joining one valence bond to the hydrogen atom, while the second valence of each oxygen atom is still "free"

BUT -

BUT -

4. The third place (column) is taken by the chemical signs of the acid-forming atoms with the designation of the valency

5. Oxygen atoms are attached to the "free" valences of the acid-forming atom according to the valence rule

Graphical representation of salt formulas

Medium salts (for example,Fe 2 SO 4 ) 3) In medium salts, all hydrogen atoms of an acid are replaced by metal atoms, therefore, when graphically depicting their formulas, the first place (first column) is occupied by the chemical signs of metal atoms with the designation of valency, and then - as in acids, that is, the second place (column) are occupied by the chemical signs of oxygen atoms, the third place (column) are the chemical signs of the acid-forming atoms, there are three of them and they are attached to six oxygen atoms. Oxygen atoms are attached to the "free" valences of the acidifier according to the valence rule

Acid salts ( for example, Ba (H 2 PO 4 ) 2) Acid salts can be considered as products of partial replacement of hydrogen atoms in acid with metal atoms, therefore, when drawing up graphic formulas of acid salts, the chemical signs of metal and hydrogen atoms with the designation of valency are written in the first place (first column)

H—

H—

Ba =

H—

H—

The second place (column) is taken by the chemical signs of oxygen atoms

Electronic configuration an atom is a numerical representation of its electron orbitals. Electronic orbitals are regions of various shapes located around an atomic nucleus in which it is mathematically likely to find an electron. Electronic configuration helps to quickly and easily tell the reader how many electron orbitals an atom has, as well as determine the number of electrons in each orbital. After reading this article, you will have mastered the method of generating electronic configurations.

Steps

Distribution of electrons using the periodic system of D. I. Mendeleev

Find the atomic number of your atom. Each atom has a specific number of electrons associated with it. Find the symbol for your atom in the periodic table. An atomic number is a positive integer starting at 1 (for hydrogen) and increasing by one for each subsequent atom. An atomic number is the number of protons in an atom, and therefore it is also the number of electrons in an atom with zero charge.

Determine the charge of an atom. Neutral atoms will have the same number of electrons as shown in the periodic table. However, charged atoms will have more or fewer electrons, depending on the amount of their charge. If you are working with a charged atom, add or subtract electrons as follows: add one electron for each negative charge and subtract one for each positive one.

• For example, a sodium atom with a charge of -1 will have an extra electron in addition to its base atomic number 11. In other words, the total atom will have 12 electrons.
• If we are talking about a sodium atom with a charge of +1, one electron must be subtracted from the base atomic number 11. Thus, the atom will have 10 electrons.

1. Remember the basic list of orbitals. As the number of electrons increases, they fill the various sublevels of the electron shell of the atom according to a certain sequence. Each sublevel of the electron shell, when filled, contains an even number of electrons. The following sublevels are available:

   Understand the electronic configuration record. Electronic configurations are recorded to clearly reflect the number of electrons in each orbital. Orbitals are written sequentially, with the number of atoms in each orbital being superscript to the right of the orbital name. The completed electronic configuration takes the form of a sequence of sublevel designations and superscripts.

   • For example, here is the simplest electronic configuration: 1s 2 2s 2 2p 6. This configuration shows that there are two electrons at the 1s sublevel, two electrons at the 2s sublevel, and six electrons at the 2p sublevel. 2 + 2 + 6 = 10 electrons in total. This is the electronic configuration of a neutral neon atom (neon atomic number is 10).

2. Remember the order of the orbitals. Keep in mind that the electron orbitals are numbered in ascending order of the electron shell number, but in ascending order of energy. For example, a filled 4s 2 orbital has less energy (or less mobile) than a partially filled or filled 3d 10, so the 4s orbital is recorded first. Once you know the order of the orbitals, you can easily fill them in according to the number of electrons in the atom. The order of filling the orbitals is as follows: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p.

   • The electronic configuration of an atom in which all orbitals are filled will have the following form: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 10 6p 6 7s 2 5f 14 6d 10 7p 6
   • Note that the above notation, when all orbitals are filled, is the electronic configuration of the element Uuo (ununoctium) 118, the highest numbered atom in the periodic table. Therefore, this electronic configuration contains all the currently known electronic sublevels of a neutrally charged atom.

3. Fill in the orbitals according to the number of electrons in your atom. For example, if we want to write down the electronic configuration of a neutral calcium atom, we must start by looking for its atomic number in the periodic table. Its atomic number is 20, so we will write the configuration of an atom with 20 electrons according to the above order.

   • Fill in the orbitals in the order above until you reach the twentieth electron. The first 1s orbital will contain two electrons, the 2s orbitals will also have two, 2p - six, 3s - two, 3p - 6, and 4s - 2 (2 + 2 + 6 +2 + 6 + 2 = 20 .) In other words, the electronic configuration of calcium is: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2.
   • Note that the orbitals are in ascending order of energy. For example, when you are ready to go to the 4th energy level, then first write down the 4s orbital, and then 3d. After the fourth energy level, you go to the fifth, where the same order is repeated. This happens only after the third energy level.

4. Use the periodic table as a visual clue. You've probably already noticed that the shape of the periodic table corresponds to the order of electronic sublevels in electronic configurations. For example, the atoms in the second column from the left always end in "s 2", while the atoms on the right edge of the thin middle section always end in "d 10", and so on. Use the periodic table as a visual guide to writing configurations - as the order in which you add to orbitals corresponds to your position in the table. See below:

   • In particular, the two leftmost columns contain atoms whose electronic configurations end in s-orbitals, the right block of the table contains atoms whose configurations end in p-orbitals, and in the lower part, atoms end in f-orbitals.
   • For example, when you write down the electronic configuration of chlorine, think like this: "This atom is located in the third row (or" period ") of the periodic table. It is also located in the fifth group of the p orbital block of the periodic system. Therefore, its electronic configuration will end in. ..3p 5
   • Please note: the elements in the region of the d and f orbitals of the table are characterized by energy levels that do not correspond to the period in which they are located. For example, the first row of the block of elements with d-orbitals corresponds to 3d orbitals, although it is located in the 4th period, and the first row of elements with f-orbitals corresponds to the 4f orbital, despite the fact that it is in the 6th period.

5. Learn the shorthand for writing long electronic configurations. The atoms on the right edge of the periodic table are called noble gases. These elements are chemically very stable. To shorten the process of writing long electron configurations, simply write in square brackets the chemical symbol of the nearest noble gas with fewer electrons than your atom, and then continue writing the electronic configuration of subsequent orbital levels. See below:

   • To understand this concept, it is helpful to write an example configuration. Let's write the configuration for zinc (atomic number 30) using the noble gas abbreviation. The complete configuration of zinc looks like this: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10. However, we see that 1s 2 2s 2 2p 6 3s 2 3p 6 is the electronic configuration of argon, a noble gas. Just replace part of the electronic configuration of zinc with the chemical symbol argon in square brackets (.)
   • So, the electronic configuration of zinc, written in an abbreviated form, is: 4s 2 3d 10.
   • Note that if you are writing the electronic configuration of a noble gas, say argon, you cannot write it! One must use the reduction of the noble gas facing this element; for argon it will be neon ().

   Using the periodic table ADOMAH

   1. Learn the ADOMAH periodic table. This method Recording the electronic configuration does not require memorization, however, it requires a revised periodic table, since in the traditional periodic table, starting from the fourth period, the period number does not correspond to the electronic shell. Find the ADOMAH Periodic Table - a special type of periodic table developed by scientist Valery Zimmerman. It is easy to find it with a short search on the Internet.

      • In the periodic table of ADOMAH, horizontal rows represent groups of elements such as halogens, noble gases, alkali metals, alkaline earth metals, etc. The vertical columns correspond to the electronic levels, and the so-called "cascades" (diagonal lines connecting blocks s, p, d and f) correspond to periods.
      • Helium is moved to hydrogen as both of these elements have a 1s orbital. Period blocks (s, p, d and f) are shown on the right side, and level numbers are shown at the bottom. Elements are shown in boxes numbered 1 through 120. These numbers are common atomic numbers that represent the total number of electrons in a neutral atom.

   2. Find your atom in the ADOMAH table. To record the electronic configuration of an element, find its symbol in the ADOMAH periodic table and cross out all elements with a higher atomic number. For example, if you need to write down the electronic configuration of erbium (68), cross out all elements from 69 to 120.

      • Note the numbers 1 through 8 at the bottom of the table. These are electronic level numbers, or column numbers. Ignore columns that contain only crossed out items. For erbium, the columns numbered 1, 2, 3, 4, 5 and 6 remain.

   3. Count the orbital sublevels to your element. Looking at the block symbols shown to the right of the table (s, p, d, and f) and the column numbers shown at the bottom, ignore the diagonal lines between blocks and break the columns into column blocks, listing them in order from bottom to top. Again, ignore the boxes with all the elements crossed out. Write down the column blocks, starting with the column number followed by the block symbol, thus: 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 6s (for erbium).

      • Note: The above electronic configuration Er is written in ascending order of the electronic sublevel number. It can also be written in the order of filling the orbitals. To do this, follow the cascades from bottom to top, and not along the columns when you write the column blocks: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 12.

   4. Count the electrons for each electronic sublevel. Count the elements in each block-column that were not crossed out, attaching one electron from each element, and write their number next to the block symbol for each block-column as follows: 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 4f 12 5s 2 5p 6 6s 2. In our example, this is the electronic configuration of erbium.

   5. Consider incorrect electronic configurations. There are eighteen typical exceptions related to the electronic configurations of atoms in the lowest energy state, also called the ground energy state. They don't obey general rule only in the last two or three positions occupied by electrons. In this case, the actual electronic configuration assumes that the electrons are in a state with a lower energy in comparison with the standard configuration of the atom. Exception atoms include:

      • Cr(..., 3d5, 4s1); Cu(..., 3d10, 4s1); Nb(..., 4d4, 5s1); Mo(..., 4d5, 5s1); Ru(..., 4d7, 5s1); Rh(..., 4d8, 5s1); Pd(..., 4d10, 5s0); Ag(..., 4d10, 5s1); La(..., 5d1, 6s2); Ce(..., 4f1, 5d1, 6s2); Gd(..., 4f7, 5d1, 6s2); Au(..., 5d10, 6s1); Ac(..., 6d1, 7s2); Th(..., 6d2, 7s2); Pa(..., 5f2, 6d1, 7s2); U(..., 5f3, 6d1, 7s2); Np(..., 5f4, 6d1, 7s2) and Cm(..., 5f7, 6d1, 7s2).
   • To find the atomic number of an atom when written in electronic configuration, simply add up all the numbers that follow the letters (s, p, d, and f). This only works for neutral atoms, if you are dealing with an ion, then nothing will work - you have to add or subtract the number of extra or lost electrons.
   • The number following the letter is a superscript, do not make a mistake in the check.
   • There is no "stability of a half-filled" sublevel. This is a simplification. Any stability that relates to the "half filled" sublevels is due to the fact that each orbital is occupied by one electron, so the repulsion between the electrons is minimized.
   • Each atom tends to a stable state, and the most stable configurations have filled sublevels s and p (s2 and p6). Noble gases have such a configuration, therefore they rarely enter into reactions and are located on the right in the periodic table. Therefore, if the configuration ends at 3p 4, then it needs two electrons to reach a stable state (it will take more energy to lose six, including electrons of the s-sublevel, so it is easier to lose four). And if the configuration ends in 4d 3, then in order to achieve a stable state, it needs to lose three electrons. In addition, half-filled sublevels (s1, p3, d5 ..) are more stable than, for example, p4 or p2; however, s2 and p6 will be even more stable.
   • When you are dealing with an ion, this means that the number of protons is not equal to the number of electrons. In this case, the charge of an atom will be shown at the top right (as a rule) of the chemical symbol. Therefore, an antimony atom with a charge of +2 has the electronic configuration 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 1. Note that 5p 3 has changed to 5p 1. Be careful when the configuration of a neutral atom ends up at sublevels other than s and p. When you pick up electrons, you can only pick them up from the valence orbitals (s and p orbitals). Therefore, if the configuration ends at 4s 2 3d 7 and the atom gets a charge of +2, then the configuration will end at 4s 0 3d 7. Please note that 3d 7 not changes, instead of losing s-orbital electrons.
   • There are conditions when the electron is forced to "go to a higher energy level." When a sublevel lacks one electron to half or full filling, take one electron from the nearest s or p-sublevel and move it to the sublevel that needs an electron.
   • There are two options for recording an electronic configuration. They can be written in ascending order of energy level numbers or in the order of filling of electron orbitals, as was shown above for erbium.
   • You can also write down the electronic configuration of an element by writing down only the valence configuration, which is the last s and p sublevels. Thus, the valence configuration of antimony will have the form 5s 2 5p 3.
   • Jonah is not the same. It is much more difficult with them. Skip two levels and follow the same pattern depending on where you started and how large the number of electrons is.

Problem 56.
Write an electron-graphic 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 symbols nl x , where n Is the principal quantum number, l - orbital quantum number (instead of it indicate the corresponding letter designation - s, p, d, f ), x - the number of electrons in a given sublevel (orbital). It should be borne in mind that the electron occupies the energy sublevel at which it has the lowest energy - the smaller amount n + 1 (Klechkovsky 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

a) Element No. 19
Since the number of electrons in an atom of this or that element is equal to its ordinal number in the table of D.I. Mendeleev, then for element 19 - potassium (K - ordinal number 19), the electronic formula has the form:

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

b) Element number 20
For element number 20 - calcium (Ca - ordinal number 20), the electronic formula is:

Valence electrons calcium 4s 2 - are located on 4s -sublevel On the valence orbital of the Ca atom there are 2 electrons. Therefore, the element is placed in the second group of the periodic system of D.I. Mendeleev.

c) Element number 21
For element number 21 - scandium (Ca - ordinal number 21), the electronic formula is:

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

Valence electrons scandium 4s 2 3d 1 - are located 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 the periodic system of D.I. Mendeleev.

d) Element number 22
For element number 22 - titanium (Ti - ordinal number 22), the electronic formula is:

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

Valence electrons of scandium 4s 2 3d 2 - are located on 4s- and 3d- sublevels. There are 4 electrons in the valence orbitals of the Ti atom. Therefore, the element is placed in the fourth group of the periodic system of D.I. Mendeleev.

e) Element number 23
For element number 23 - vanadium (V - ordinal number 23), the electronic formula is:

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

Valence electrons of scandium 4s 2 3d 3 - are located 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 the periodic system of D.I. Mendeleev.

f) Element No. 24
For the element chromium (Cr - ordinal number 24), the electronic formula is:

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

Valence electrons chrome 4s 1 3d 5 - are located 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 the periodic system of D.I. Mendeleev.
In the chromium atom, one electron from the 4s sublevel goes over 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 there are not 4 but 5 electrons on the 3d-sublevel - all cells are filled with one electron. Thus, the valence electron configuration 4s 1 3d 5 is energetically more favorable to the chromium atom than the 4s 2 3d 4.

g) Element number 25 - manganese (Mn - ordinal number 25), the electronic formula has the form:

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

Valence electrons of manganese 4s 2 3d 5 - are located 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 the periodic system of D.I. Mendeleev.

h) Element number 26 - iron (Fe - ordinal number 26), the 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 located 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 the periodic system of D.I. Mendeleev.

j) Element number 27 - sablet (Co - ordinal number 27), the electronic formula has the form:

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

Valence electrons sablet 4s 2 3d 7 - are located 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 the periodic system of D.I. Mendeleev.

k) Element number 28 - nickel (Ni - ordinal number 28), the electronic formula has the form:

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

Valence electrons of nickel 4s 2 3d 8 - are located 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 the periodic system of D.I. Mendeleev.

m) Element number 29 - copper (Cu - ordinal number 29), the 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 located on 4s- and 3d- sublevels. There are 11 electrons in the valence orbitals of the Cu atom. Therefore, the element is placed in the eleventh group of the periodic system of D.I. Mendeleev.
A breakthrough is observed for a copper atom ( "failure"): one electron of the 4s sublevel goes over to the 3d sublevel. This is explained by the fact that the state of the atom is considered more energetically favorable if there are not 9, but 10 electrons on the d-sublevel. 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, but only one electron on the fifth. To fill the fifth d-cell of the 3d sublevel, one electron of the 4s sublevel goes over to the 3d sublevel, as if " falls through Thus, the valence electron configuration 4s 1 3d 10 is energetically more favorable to the copper atom than the 4s 2 3d 9.

m) Element number 30 - zinc (Zn - ordinal number 30), the electronic formula is:

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

Zinc valence electrons 4s 2 3d 10 - are located 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 the periodic system of D.I. Mendeleev.

o) Element number 31 - gallium (Ga - ordinal number 31), the electronic formula is:

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

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

n) Element number 32 - germanium (Ge - ordinal number 32), the electronic formula has the form:

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

Valence electrons of germanium 4s 2 3d 10 4p 2 - are located 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 the periodic system of D.I. Mendeleev.

p) Element number 33 - arsenic (As - ordinal number 33), the electronic formula has the form:

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

Valence electrons arsenic 4s 2 3d 10 4p 3 - are located 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 the periodic system of D.I. Mendeleev.

c) Element number 34 - selenium (Se - ordinal number 34), the electronic formula is:

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

Valence electrons Selena 4s 2 3d 10 4p 4 - are located 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 the periodic system of D.I. Mendeleev.

c) Element number 35 - bromine (Br - ordinal number 35), the electronic formula is:

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

Valence electrons bromine 4s 2 3d 10 4 p 5 - are located 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 the periodic system of D.I. Mendeleev.

r) Element number 36 - krypton (Kr - ordinal number 36), the electronic formula has the form:

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

Valence electrons krypton 4s 2 3d 10 4p 6 - are located 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 the periodic system of D.I. Mendeleev.

Algorithm for drawing up an electronic formula for an element:

1. Determine the number of electrons in an atom using the Periodic Table of Chemical Elements of D.I. Mendeleev.

2. By the number of the period in which the element is located, determine the number of energy levels; the number of electrons in the last electronic level corresponds to the group number.

3. Divide the levels into sublevels and orbitals and fill them with electrons in accordance with the rules for filling the orbitals:

It must be remembered that there is a maximum of 2 electrons at the first level. 1s 2, on the second - a maximum of 8 (two s and six R: 2s 2 2p 6), on the third - a maximum of 18 (two s, six p and ten d: 3s 2 3p 6 3d 10).

• Principal Quantum Number n should be minimal.
• First filled s- sublevel then p-, d- b f- sublevels.
• Electrons fill the orbitals in ascending order of orbital energy (Klechkovsky's rule).
• Within the sublevel, the electrons first occupy free orbitals one at a time, and only then form pairs (Hund's rule).
• There can be no more than two electrons in one orbital (Pauli's principle).

Examples.

1. Let's compose the electronic formula of nitrogen. In the periodic table, nitrogen is at number 7.

2. Let's compose the electronic formula of argon. Argon is at number 18 on the periodic table.

1s 2 2s 2 2p 6 3s 2 3p 6.

3. Let's compose the electronic formula of chromium. Chromium is found at number 24 on the periodic table.

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

Zinc energy diagram.

4. Let's compose the electronic formula of zinc. Zinc is found at number 30 on the periodic table.

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

Note that part of the electronic formula, namely 1s 2 2s 2 2p 6 3s 2 3p 6, is the electronic formula of argon.

The electronic formula of zinc can be represented as.