Examples of problem solving. Electronic configuration of an atom Which of the proposed particles corresponds to the electronic configuration

Electronic configuration of an atom is a numerical representation of its electron orbitals. Electron orbitals are regions of various shapes located around the atomic nucleus in which it is mathematically probable that an electron will be found. Electronic configuration helps 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 master the method of drawing up 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 certain number of electrons associated with it. Find your atom's symbol on the periodic table. The atomic number is a positive integer starting at 1 (for hydrogen) and increasing by one for each subsequent atom. Atomic number is the number of protons in an atom, and therefore it is also the number of electrons of an atom with zero charge.

Determine the charge of an atom. Neutral atoms will have the same number of electrons as shown on the periodic table. However, charged atoms will have more or less electrons, depending on the magnitude 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 charge.

• For example, a sodium atom with charge -1 will have an extra electron in addition to its base atomic number 11. In other words, the atom will have a total of 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 in an atom increases, they fill the various sublevels of the atom's electron shell according to a specific sequence. Each sublevel of the electron shell, when filled, contains an even number of electrons. The following sublevels are available:

   Understand electronic configuration notation. Electron configurations are written to clearly show the number of electrons in each orbital. Orbitals are written sequentially, with the number of atoms in each orbital written as a superscript to the right of the orbital name. The completed electronic configuration takes the form of a sequence of sublevel designations and superscripts.

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

2. Remember the order of the orbitals. Keep in mind that electron orbitals are numbered in order of increasing electron shell number, but arranged in increasing order of energy. For example, a filled 4s 2 orbital has lower energy (or less mobility) than a partially filled or filled 3d 10 orbital, so the 4s orbital is written first. Once you know the order of the orbitals, you can easily fill them 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 be as follows: 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 entry, when all orbitals are filled, is the electron configuration of 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 the orbitals according to the number of electrons in your atom. For example, if we want to write down the electron configuration of a neutral calcium atom, we must start by looking up 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 the orbitals according to the order above until you reach the twentieth electron. The first 1s orbital will have two electrons, the 2s orbital will also have two, the 2p will have six, the 3s will have two, the 3p will have 6, and the 4s will have 2 (2 + 2 + 6 +2 +6 + 2 = 20 .) In other words, the electronic configuration of calcium has the form: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 .
   • Note that the orbitals are arranged in order of increasing energy. For example, when you are ready to move to the 4th energy level, first write down the 4s orbital, and then 3d. After the fourth energy level, you move 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 cue. You've probably already noticed that the shape of the periodic table corresponds to the order of the electron sublevels in the electron configurations. For example, the atoms in the second column from the left always end in "s 2", and the atoms on the right edge of the thin middle part always end in "d 10", etc. Use the periodic table as a visual guide to writing configurations - how the order in which you add to the orbitals corresponds to your position in the table. See below:

   • Specifically, the leftmost two 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 the bottom half contains atoms that 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 table. Therefore, its electronic configuration will end with. ..3p 5
   • Note that elements in the d and f orbital region 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 a 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 a 4f orbital, despite being in the 6th period.

5. Learn abbreviations for writing long electron 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 the chemical symbol of the nearest noble gas with fewer electrons than your atom in square brackets, and then continue writing the electron configuration of subsequent orbital levels. See below:

   • To understand this concept, it will be helpful to write an example configuration. Let's write the configuration of zinc (atomic number 30) using the abbreviation that includes the noble gas. 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 electron configuration of argon, a noble gas. Simply replace part of the electronic configuration for zinc with the chemical symbol for argon in square brackets (.)
   • So, the electronic configuration of zinc, written in abbreviated form, has the form: 4s 2 3d 10 .
   • Please note that if you are writing the electronic configuration of a noble gas, say argon, you cannot write it! One must use the abbreviation for the noble gas preceding this element; for argon it will be neon ().

   Using the periodic table ADOMAH

   1. Master the periodic table ADOMAH. This method of recording the electronic configuration does not require memorization, but requires a modified periodic table, since in the traditional periodic table, starting from the fourth period, the period number does not correspond to the electron shell. Find the periodic table ADOMAH - a special type of periodic table developed by scientist Valery Zimmerman. It is easy to find with a short internet search.

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

   2. Find your atom in the ADOMAH table. To write the electronic configuration of an element, look up its symbol on the periodic table ADOMAH and cross out all elements with a higher atomic number. For example, if you need to write the electron 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 numbers of electronic levels, or numbers of columns. Ignore columns that contain only crossed out items. For erbium, columns numbered 1,2,3,4,5 and 6 remain.

   3. Count the orbital sublevels up 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 base, ignore the diagonal lines between the blocks and break the columns into column blocks, listing them in order from bottom to top. Again, ignore blocks that have all the elements crossed out. Write column blocks starting from the column number followed by the block symbol, thus: 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 6s (for erbium).

      • Please note: The above electron configuration of Er is written in ascending order of electron sublevel number. It can also be written in order of filling the orbitals. To do this, follow the cascades from bottom to top, rather than columns, when you write 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 electron sublevel. Count the elements in each column block that have not been crossed out, attaching one electron from each element, and write their number next to the block symbol for each column block thus: 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. Be aware of incorrect electronic configurations. There are eighteen typical exceptions that relate to the electronic configurations of atoms in the lowest energy state, also called the ground energy state. They do not obey the general rule only for 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 compared to 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 it is written in electron configuration form, simply add up all the numbers that follow the letters (s, p, d, and f). This only works for neutral atoms, if you're dealing with an ion it won't work - you'll 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 test.
   • There is no "half-full" sublevel stability. This is a simplification. Any stability that is attributed to "half-filled" sublevels is due to the fact that each orbital is occupied by one electron, thus minimizing repulsion between electrons.
   • Each atom tends to a stable state, and the most stable configurations have the s and p sublevels filled (s2 and p6). Noble gases have this configuration, so they rarely react and are located on the right in the periodic table. Therefore, if a configuration ends in 3p 4, then it needs two electrons to reach a stable state (to lose six, including the s-sublevel electrons, requires more energy, so losing four is easier). And if the configuration ends in 4d 3, then 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. The charge of the atom in this case will be depicted at the top right (usually) of the chemical symbol. Therefore, an antimony atom with charge +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 neutral atom configuration ends in sublevels other than s and p. When you take away electrons, you can only take them from the valence orbitals (s and p orbitals). Therefore, if the configuration ends with 4s 2 3d 7 and the atom receives a charge of +2, then the configuration will end with 4s 0 3d 7. Please note that 3d 7 Not changes, electrons from the s orbital are lost instead.
   • There are conditions when an electron is forced to "move to a higher energy level." When a sublevel is one electron short of being half or full, take one electron from the nearest s or p sublevel and move it to the sublevel that needs the electron.
   • There are two options for recording the electronic configuration. They can be written in increasing order of energy level numbers or in the order of filling electron orbitals, as was shown above for erbium.
   • You can also write the electronic configuration of an element by writing only the valence configuration, which represents the last s and p sublevel. Thus, the valence configuration of antimony will be 5s 2 5p 3.
   • Ions are not the same. It's 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.

Electronic configuration of an atom is a formula showing the arrangement of electrons in an atom by levels and sublevels. After studying the article, you will learn where and how electrons are located, get acquainted with quantum numbers and be able to construct the electronic configuration of an atom by its number; at the end of the article there is a table of elements.

Why study the electronic configuration of elements?

Atoms are like a construction set: there is a certain number of parts, they differ from each other, but two parts of the same type are absolutely the same. But this construction set is much more interesting than the plastic one and here’s why. The configuration changes depending on who is nearby. For example, oxygen next to hydrogen Maybe

turn into water, when near sodium it turns into gas, and when near iron it completely turns it into rust.

To answer the question of why this happens and predict the behavior of an atom next to another, it is necessary to study the electronic configuration, which will be discussed below.

How many electrons are in an atom?

By observing the behavior of the electron, certain patterns were derived; they are described by quantum numbers, there are four in total:

• Principal quantum number
• Orbital quantum number
• Magnetic quantum number
• Spin quantum number

Orbital

Further, instead of the word orbit, we will use the term “orbital”; an orbital is the wave function of an electron; roughly, it is the region in which the electron spends 90% of its time.

N - level
L - shell
M l - orbital number
M s - first or second electron in the orbital

Orbital quantum number l

As a result of studying the electron cloud, they found that depending on the energy level, the cloud takes four main forms: a ball, dumbbells and two other, more complex ones.

In order of increasing energy, these forms are called the s-, p-, d- and f-shell.
Each of these shells can have 1 (on s), 3 (on p), 5 (on d) and 7 (on f) orbitals. The orbital quantum number is the shell in which the orbitals are located. The orbital quantum number for the s, p, d and f orbitals takes the values ​​0,1,2 or 3, respectively.
There is one orbital on the s-shell (L=0) - two electrons
There are three orbitals on the p-shell (L=1) - six electrons

There are five orbitals on the d-shell (L=2) - ten electrons

There are seven orbitals on the f-shell (L=3) - fourteen electrons

Magnetic quantum number m l

There are three orbitals on the p-shell, they are designated by numbers from -L to +L, that is, for the p-shell (L=1) there are orbitals “-1”, “0” and “1”.
The magnetic quantum number is denoted by the letter m l.

Inside the shell, it is easier for electrons to be located in different orbitals, so the first electrons fill one in each orbital, and then a pair of electrons is added to each one.

Consider the d-shell:

The d-shell corresponds to the value L=2, that is, five orbitals (-2,-1,0,1 and 2), the first five electrons fill the shell taking the values ​​M l =-2, M l =-1, M l =0 , M l =1,M l =2.

The main quantum number is the energy level; currently seven energy levels are known, each indicated by an Arabic numeral: 1,2,3,...7. The number of shells at each level is equal to the level number: there is one shell on the first level, two on the second, etc.

Electron number

So, any electron can be described by four quantum numbers, the combination of these numbers is unique for each position of the electron, take the first electron, the lowest energy level is N = 1, at the first level there is one shell, the first shell at any level has the shape of a ball (s -shell), i.e. L=0, the magnetic quantum number can take only one value, M l =0 and the spin will be equal to +1/2.

If we take the fifth electron (in whatever atom it is), then the main quantum numbers for it will be: N=2, L=1, M=-1, spin 1/2.

DEFINITION Argon

- a chemical element belonging to the class of inert (noble) gases. Located in the third period of VIII group A of the subgroup, if you look at the short-period table, or in the 18th group, if you look at the long-period table.

Designation - Ar. Belongs to the family of p-elements. The serial number is 18. Atomic weight is 39.948 amu.

Electronic structure of the argon atom

An argon atom consists of a positively charged nucleus (+18), consisting of 18 protons and 22 neutrons, around which 18 electrons move in 3 orbits.

Fig.1. Schematic structure of the argon atom.

1The distribution of electrons among orbitals is as follows: 2 2The distribution of electrons among orbitals is as follows: 2 2s 6 3The distribution of electrons among orbitals is as follows: 2 3s 6 .

p

The outer energy level of the argon atom is completely complete - 8 electrons. The energy diagram of the ground state takes the following form: An excited state, despite the presence of a vacant 3 d

-there is no orbital. This is why neon is classified as an inert gas. Chemically it is inactive.

Examples of problem solving

EXAMPLE 1

EXAMPLE 2	Exercise The distribution of electrons among orbitals is as follows: What are all the quantum numbers for electrons that are at 4
- sublevel?	Solution Each electron can be characterized by a set of four quantum numbers: the main one, which is determined by the number of the level, orbital, which is determined by the number of the sublevel, magnetic and spin. The distribution of electrons among orbitals is as follows: On

- the sublevel of the 4th level contains two electrons:

Let's look at task No. 1 from the Unified State Exam options for 2016.

Task No. 1.

The electronic formula of the outer electron layer 3s²3p6 corresponds to the structure of each of the two particles:

1. Arº and Kº 2. Cl‾ and K+ 3. S²‾ and Naº 4. Clº and Ca2+ among the answer options are atoms in unexcited and excited states, that is, the electronic configuration of, say, a potassium ion does not correspond to its position in the periodic table. Let's consider option 1 Arº and Kº. Let's write their electronic configurations: Arº: 1s2 2s2 2p6 3s2 3p6; Kº: 1s2 2s2 2p6 3s2 3p6 4s1 - suitable electronic configuration only for argon. Let's consider answer option No. 2 - Cl‾ and K+. K+: 1s2 2s2 2p6 3s2 4s0; Cl‾: 1s2 2s2 2p6 3s2 3p6. Hence, the correct answer is 2.

Task No. 2.

1. Caº 2. K+ 3. Cl+ 4. Zn2+

1. Arº and Kº 2. Cl‾ and K+ 3. S²‾ and Naº 4. Clº and Ca2+ for we write the electronic configuration of argon: 1s2 2s2 2p6 3s2 3p6. Calcium is not suitable because it has 2 more electrons. For potassium: 1s2 2s2 2p6 3s2 3p6 4s0. The correct answer is 2.

Task No. 3.

An element whose atomic electronic configuration is 1s2 2s2 2p6 3s2 3p4 forms a hydrogen compound

1. CH4 2. SiH4 3. H2O 4. H2S

1. Arº and Kº 2. Cl‾ and K+ 3. S²‾ and Naº 4. Clº and Ca2+ Let's look at the periodic table, the sulfur atom has this electronic configuration. The correct answer is 4.

Task No. 4.

The atoms of magnesium and

1. Calcium 2. Chromium 3. Silicon 4. Aluminum

1. Arº and Kº 2. Cl‾ and K+ 3. S²‾ and Naº 4. Clº and Ca2+ Magnesium has an external energy level configuration: 3s2. For calcium: 4s2, for chromium: 4s2 3d4, for silicon: 3s2 2p2, for aluminum: 3s2 3p1. The correct answer is 1.

Task No. 5.

The argon atom in the ground state corresponds to the electron configuration of the particle:

1. S²‾ 2. Zn2+ 3. Si4+ 4. Seº

1. Arº and Kº 2. Cl‾ and K+ 3. S²‾ and Naº 4. Clº and Ca2+ The electronic configuration of argon in the ground state is 1s2 2s2 2p6 3s2 3p6. S²‾ has the electronic configuration: 1s2 2s2 2p6 3s2 3p(4+2). The correct answer is 1.

Task No. 6.

Phosphorus and phosphorus atoms have a similar configuration of the outer energy level.

1. Ar 2. Al 3. Cl 4. N

1. Arº and Kº 2. Cl‾ and K+ 3. S²‾ and Naº 4. Clº and Ca2+ Let's write the electronic configuration of the outer level of the phosphorus atom: 3s2 3p3.

For aluminum: 3s2 3p1;

For argon: 3s2 3p6;

For chlorine: 3s2 3p5;

For nitrogen: 2s2 2p3.

The correct answer is 4.

Task No. 7.

The electron configuration 1s2 2s2 2p6 3s2 3p6 corresponds to the particle

1. S4+ 2. P3- 3. Al3+ 4. O2-

1. Arº and Kº 2. Cl‾ and K+ 3. S²‾ and Naº 4. Clº and Ca2+ this electronic configuration corresponds to the argon atom in the ground state. Let's consider the answer options:

S4+: 1s2 2s2 2p6 3s2 2p0

P3-: 1s2 2s2 2p6 3s2 3p(3+3)

The correct answer is 2.

Task No. 8.

Which electronic configuration corresponds to the distribution of valence electrons in a chromium atom:

1. 3d2 4s2 2. 3s2 3p4 3. 3d5 4s1 4. 4s2 4p6

1. Arº and Kº 2. Cl‾ and K+ 3. S²‾ and Naº 4. Clº and Ca2+ Let's write the electronic configuration of chromium in the ground state: 1s2 2s2 2p6 3s2 3p6 4s1 3d5. Valence electrons are located in the last two sublevels 4s and 3d (here one electron jumps from the s to d sublevel). The correct answer is 3.

Task No. 9.

The atom contains three unpaired electrons in the outer electronic level in the ground state.

1. Titanium 2. Silicon 3. Magnesium 4. Phosphorus

1. Arº and Kº 2. Cl‾ and K+ 3. S²‾ and Naº 4. Clº and Ca2+ In order to have 3 unpaired electrons, the element must be in group 5. Hence, the correct answer is 4.

Task No. 10.

An atom of a chemical element whose highest oxide is RO2 has the external level configuration:

1. ns2 np4 2. ns2 np2 3. ns2 4. ns2 np1

1. Arº and Kº 2. Cl‾ and K+ 3. S²‾ and Naº 4. Clº and Ca2+ this element has an oxidation state (in this compound) of +4, that is, it must have 4 valence electrons in the outer level. Hence, the correct answer is 2.

(you might think that the correct answer is 1, but such an atom would have a maximum oxidation state of +6 (since there are 6 electrons in the outer level), but we need the higher oxide to have the formula RO2, and such an element would have the higher oxide RO3)

Assignments for independent work.

1. Electronic configuration 1s2 2s2 2p6 3s2 3p5 corresponds to an atom

1. Aluminum 2. Nitrogen 3. Chlorine 4. Fluorine

2. The particle has an eight-electron outer shell

1. P3+ 2. Mg2+ 3. Cl5+ 4. Fe2+

3. The atomic number of an element whose atomic electronic structure is 1s2 2s2 2p3 is equal to

1. 5 2. 6 3. 7 4. 4

4. The number of electrons in the copper ion Cu2+ is

1. 64 2. 66 3. 29 4. 27

5. The nitrogen atoms and

1. Sulfur 2. Chlorine 3. Arsenic 4. Manganese

6. Which compound contains a cation and an anion with the electron configuration 1s2 2s2 2p6 3s3 3p6?

1. NaCl 2. NaBr 3. KCl 4. KBr

7. The number of electrons in the iron ion Fe2+ is

1. 54 2. 28 3. 58 4. 24

8. The ion has the electronic configuration of an inert gas

1. Cr2+ 2. S2- 3. Zn2+ 4. N2-

9. The fluorine and fluorine atoms have a similar configuration of the outer energy level

1. Oxygen 2. Lithium 3. Bromine 4. Neon

10. An element whose atomic electronic formula is 1s2 2s2 2p6 3s2 3p4 corresponds to a hydrogen compound

1. HCl 2. PH3 3. H2S 4. SiH4

This note uses tasks from the 2016 Unified State Exam collection edited by A.A. Kaverina.