The electronic formula of the sodium atom. Electronic element formula

It is written in the form of so-called electronic formulas. In electronic formulas, the letters s, p, d, f denote the energy sublevels of electrons; the numbers in front of the letters indicate the energy level in which the given electron is located, and the index at the top right indicates the number of electrons in this sublevel. To compose the electronic formula of an atom of any element, it is enough to know the number of this element in the periodic table and fulfill the basic provisions that govern the distribution of electrons in the atom.

The structure of the electron shell of an atom can also be depicted as a diagram of the distribution of electrons in energy cells.

For iron atoms, such a scheme is as follows:

This diagram clearly shows the fulfillment of the Gund rule. At the 3d-sublevel, the maximum number of cells (four) is filled with unpaired electrons. The image of the structure of the electron shell in the atom in the form of electronic formulas and in the form of diagrams does not clearly reflect the wave properties of the electron.

The wording of the periodic law as amendedYES. Mendeleev : the properties of simple bodies, as well as the shapes and properties of compounds of elements, are in periodic dependence of the value of the atomic weights of elements.

Modern formulation of the Periodic Law: the properties of elements, as well as the forms and properties of their compounds, are periodically dependent on the magnitude of the charge of the nucleus of their atoms.

Thus, the positive charge of the nucleus (and not the atomic mass) turned out to be a more accurate argument on which the properties of elements and their compounds depend.

Valence- it is the number of chemical bonds by which one atom is bonded to another.
The valence capabilities of an atom are determined by the number of unpaired electrons and the presence of free atomic orbitals at the outer level. The structure of the outer energy levels of atoms of chemical elements and determines mainly the properties of their atoms. Therefore, these levels are called valence levels. Electrons of these levels, and sometimes of pre-outer levels, can take part in the formation of chemical bonds. Such electrons are also called valence electrons.

Stoichiometric valencechemical element - this is the number of equivalents that a given atom can attach to itself, or is the number of equivalents in an atom.

Equivalents are determined by the number of attached or substituted hydrogen atoms, therefore the stoichiometric valence is equal to the number of hydrogen atoms with which a given atom interacts. But not all elements freely interact, but practically all elements with oxygen, therefore the stoichiometric valence can be defined as the doubled number of attached oxygen atoms.

For example, the stoichiometric valence of sulfur in hydrogen sulfide H 2 S is 2, in SO 2 oxide - 4, in SO 3 -6 oxide.

When determining the stoichiometric valence of an element according to the formula of a binary compound, one should be guided by the rule: the total valence of all atoms of one element must be equal to the total valence of all atoms of the other element.

Oxidation statealso characterizes the composition of a substance and is equal to the stoichiometric valence with a plus sign (for a metal or more electropositive element in a molecule) or minus.

1. In simple substances, the oxidation state of the elements is zero.

2. The oxidation state of fluorine in all compounds is -1. The rest of the halogens (chlorine, bromine, iodine) with metals, hydrogen and other more electropositive elements also have an oxidation state of -1, but in compounds with more electronegative elements, they have positive oxidation states.

3. Oxygen in the compounds has an oxidation state of -2; the exception is hydrogen peroxide H 2 O 2 and its derivatives (Na 2 O 2, BaO 2, etc., in which oxygen has an oxidation state of -1, as well as oxygen fluoride OF 2, in which the oxidation state of oxygen is +2.

4. Alkaline elements (Li, Na, K, etc.) and elements of the main subgroup of the second group of the Periodic table (Be, Mg, Ca, etc.) always have an oxidation state equal to the group number, that is, +1 and +2, respectively ...

5. All elements of the third group, except for thallium, have a constant oxidation state equal to the group number, i.e. +3.

6. The highest oxidation state of an element is equal to the number of the group of the Periodic system, and the lowest is the difference: group number - 8. For example, the highest oxidation state of nitrogen (it is located in the fifth group) is +5 (in nitric acid and its salts), and the lowest is -3 (in ammonia and ammonium salts).

7. The oxidation states of the elements in the compound cancel each other out so that their sum for all atoms in a molecule or a neutral formula unit is zero, and for an ion - its charge.

These rules can be used to determine the unknown oxidation state of an element in a compound, if the oxidation states of the others are known, and to formulate multielement compounds.

Oxidation degree (oxidative number,) — auxiliary conditional value for recording the processes of oxidation, reduction and redox reactions.

Concept oxidation state is often used in inorganic chemistry instead of the concept valence... The oxidation state of an atom is equal to the numerical value of the electric charge attributed to the atom, assuming that the electron pairs that make the bond are completely biased toward more electronegative atoms (that is, assuming that the compound is composed of only ions).

The oxidation state corresponds to the number of electrons that must be attached to a positive ion to reduce it to a neutral atom, or subtract from a negative ion to oxidize it to a neutral atom:

Al 3+ + 3e - → Al
S 2− → S + 2e - (S 2− - 2e - → S)

The properties of elements, depending on the structure of the electron shell of the atom, vary by periods and groups of the periodic table. Since in a series of analogous elements the electronic structures are only similar, but not identical, then when passing from one element in a group to another, they observe not a simple repetition of properties, but their more or less clearly expressed regular change.

The chemical nature of an element is due to the ability of its atom to lose or gain electrons. This ability is quantified by the values \u200b\u200bof ionization energies and electron affinity.

Ionization energy (E and) is the minimum amount of energy required for detachment and complete removal of an electron from an atom in the gas phase at T \u003d 0

K without transferring kinetic energy to the liberated electron with the transformation of the atom into a positively charged ion: E + Ei \u003d E + + e-. The ionization energy is a positive value and has the lowest values \u200b\u200bfor alkali metal atoms and the highest for noble (inert) gas atoms.

Electron affinity (Ee) is the energy released or absorbed when an electron attaches to an atom in the gas phase at T \u003d 0

K with the transformation of an atom into a negatively charged ion without transferring kinetic energy to the particle:

E + e- \u003d E- + Ee.

Halogens, especially fluorine (Ee \u003d -328 kJ / mol), have the highest electron affinity.

The values \u200b\u200bof E and Ee are expressed in kilojoules per mole (kJ / mol) or in electron-volts per atom (eV).

The ability of a bound atom to shift the electrons of chemical bonds to itself, increasing the electron density around itself is called electronegativity.

This concept was introduced into science by L. Pauling. Electronegativitydenoted by the symbol ÷ and characterizes the tendency of a given atom to attach electrons when it forms a chemical bond.

According to R. Maliken, the electronegativity of an atom is estimated by the half-sum of the ionization energies and the electron affinity of free atoms ÷ \u003d (Ee + Ei) / 2

In periods, there is a general tendency towards an increase in the ionization energy and electronegativity with an increase in the atomic nucleus charge; in groups, these values \u200b\u200bdecrease with an increase in the ordinal number of the element.

It should be emphasized that a constant value of electronegativity cannot be attributed to an element, since it depends on many factors, in particular on the valence state of the element, the type of compound it enters into, the number and type of neighboring atoms.

Atomic and ionic radii. The sizes of atoms and ions are determined by the size of the electron shell. According to quantum mechanical concepts, the electron shell has no strictly defined boundaries. Therefore, the radius of a free atom or ion can be taken as theoretically calculated distance from the core to the position of the main maximum of the density of the outer electron clouds. This distance is called the orbital radius. In practice, the values \u200b\u200bof the radii of atoms and ions in compounds are usually used, calculated from experimental data. At the same time, covalent and metallic radii of atoms are distinguished.

Dependence of atomic and ionic radii on the charge of the nucleus of an atom of an element and is periodic... In periods as the atomic number increases, the radii tend to decrease. The largest decrease is characteristic of elements of small periods, since their external electronic level is filled. At large periods in the families of d- and f-elements, this change is less abrupt, since in them the filling of electrons occurs in the pre-outer layer. In subgroups, the radii of atoms and ions of the same type generally increase.

The periodic table of elements is a clear example of the manifestation of various kinds of periodicity in the properties of elements, which is observed horizontally (in the period from left to right), vertically (in a group, for example, from top to bottom), diagonally, i.e. some property of the atom increases or decreases, but the periodicity remains.

In the period from left to right (→), the oxidizing and non-metallic properties of the elements increase, while the reducing and metallic properties decrease. So, of all elements of the 3rd period, sodium will be the most active metal and the strongest reducing agent, and chlorine will be the strongest oxidizing agent.

Chemical bond- it is the interconnection of atoms in a molecule, or crystal lattice, as a result of the action between atoms of electric forces of attraction.

This is the interaction of all electrons and all nuclei, leading to the formation of a stable, polyatomic system (radical, molecular ion, molecule, crystal).

The chemical bond is carried out by valence electrons. According to modern concepts, the chemical bond has an electronic nature, but it is carried out in different ways. Therefore, there are three main types of chemical bonds: covalent, ionic, metallic. Between the molecules there is hydrogen bond, and happen van der Waals interactions.

The main characteristics of the chemical bond include:

- bond length - this is the internuclear distance between chemically bonded atoms.

It depends on the nature of the interacting atoms and on the multiplicity of the bond. With an increase in the multiplicity, the bond length decreases, and, consequently, its strength increases;

- the multiplicity of the bond - is determined by the number of electron pairs connecting two atoms. As the multiplicity increases, the binding energy increases;

- connection angle- the angle between the imaginary straight lines passing through the nuclei of two chemically interconnected neighboring atoms;

Binding energy E CB - this is the energy that is released during the formation of this bond and is spent on its breaking, kJ / mol.

Covalent bond - A chemical bond formed by the sharing of a pair of electrons with two atoms.

The explanation of the chemical bond by the appearance of common electron pairs between atoms formed the basis of the spin theory of valence, the instrument of which is valence bond method (MVS) discovered by Lewis in 1916. For the quantum-mechanical description of the chemical bond and the structure of molecules, another method is used - molecular orbital method (MMO) .

Valence bond method

The basic principles of the formation of a chemical bond according to MFM:

1. A chemical bond is formed by valence (unpaired) electrons.

2. Electrons with antiparallel spins belonging to two different atoms become common.

3. A chemical bond is formed only if, when two or more atoms approach each other, the total energy of the system decreases.

4. The main forces acting in the molecule are of electrical, Coulomb origin.

5. The bond is stronger, the more the interacting electron clouds overlap.

There are two mechanisms for the formation of a covalent bond:

Exchange mechanism. The bond is formed by socializing the valence electrons of two neutral atoms. Each atom gives one unpaired electron to a common electron pair:

Figure: 7. Exchange mechanism of covalent bond formation: and - non-polar; b - polar

Donor-acceptor mechanism. One atom (donor) provides an electron pair, and another atom (acceptor) provides a free orbital for this pair.

Connections, educatedby donor-acceptor mechanism, refer to complex compounds

Figure: 8. Donor-acceptor mechanism of covalent bond formation

The covalent bond has certain characteristics.

Saturability - the property of atoms to form a strictly defined number of covalent bonds. Due to the saturation of the bonds, the molecules have a certain composition.

Directivity - t ... That is, the bond is formed in the direction of the maximum overlap of electron clouds . Relative to the line connecting the centers of the atoms forming the bond are distinguished: σ and π (Fig. 9): σ-bond - formed by overlapping AO along the line connecting the centers of interacting atoms; A π-bond is a bond arising in the direction of the axis of the perpendicular line connecting the nuclei of the atom. The directionality of the bond determines the spatial structure of the molecules, that is, their geometric shape. Hybridization - it is a change in the shape of some orbitals during the formation of a covalent bond to achieve more effective overlapping of the orbitals. The chemical bond formed with the participation of the electrons of the hybrid orbitals is stronger than the bond with the participation of the electrons of the non-hybrid s and p orbitals, as there is more overlap. There are the following types of hybridization (Fig. 10, Table 31): sp-hybridization - one s-orbital and one p-orbital turn into two identical "hybrid" orbitals, the angle between the axes of which is 180 °. The molecules in which sp-hybridization is carried out have a linear geometry (BeCl 2).

sp 2 -hybridization - one s-orbital and two p-orbitals turn into three identical "hybrid" orbitals, the angle between the axes of which is 120 °. The molecules in which sp 2 -hybridization is carried out have a planar geometry (BF 3, AlCl 3).

sp 3-hybridization - one s-orbital and three p-orbitals transform into four identical "hybrid" orbitals, the angle between the axes of which is 109 ° 28 ". Molecules in which sp 3 -hybridization is carried out have a tetrahedral geometry (CH 4 , NH 3).

Figure: 10. Types of hybridizations of valence orbitals: a - sp-hybridization of valence orbitals; b - sp 2 -hybridization of valence orbitals; in - sp 3-hybridization of valence orbitals

MENDELEEV'S PERIODIC TABLE

The construction of Mendeleev's periodic table of chemical elements corresponds to the characteristic periods of the theory of numbers and orthogonal bases. Supplementing Hadamard matrices with matrices of even and odd orders creates a structural basis of nested matrix elements: matrices of the first (Odin), second (Euler), third (Mersenne), fourth (Hadamard) and fifth (Fermat) orders.

It is easy to see that the orders 4 k Hadamard matrices correspond to inert elements with an atomic mass that is a multiple of four: helium 4, neon 20, argon 40 (39.948), etc., but also the basics of life and digital technology: carbon 12, oxygen 16, silicon 28, germanium 72.

The impression is that with Mersenne matrices of order 4 k–1, on the contrary, everything active, poisonous, destructive and corrosive is connected. But it is also radioactive elements - energy sources, and lead 207 (the end product, poisonous salts). Fluorine is, of course, 19. The orders of the Mersenne matrices correspond to a sequence of radioactive elements called the actinium series: uranium 235, plutonium 239 (an isotope that is a more powerful source of atomic energy than uranium), etc. It is also the alkali metals lithium 7, sodium 23 and potassium 39.

Gallium - atomic weight 68

Orders 4 k–2 Euler matrices (double Mersenne) corresponds to nitrogen 14 (the basis of the atmosphere). Table salt is formed by two "mersennopodny" atoms sodium 23 and chlorine 35, together this combination is typical, just for the Euler matrices. The more massive chlorine with a weight of 35.4 does not reach the Hadamard dimension of 36. Crystals of table salt: a cube (! That is, a meek character, Hadamars) and an octahedron (more challenging, this is undoubted Euler).

In atomic physics, the transition iron 56 - nickel 59 is the boundary between the elements that give energy during the fusion of a larger nucleus (hydrogen bomb) and decay (uranium). The order of 58 is famous for the fact that for it there are not only analogs of Hadamard matrices in the form of Belevich matrices with zeros on the diagonal, for it there are also no many weighted matrices - the nearest orthogonal W (58,53) has 5 zeros in each column and row (deep gap ).

In the series corresponding to Fermat matrices and their substitutions of orders 4 k+1, by the will of fate 257 farms. Nothing to say, an exact hit. There is also gold 197. Copper 64 (63.547) and silver 108 (107.868), symbols of electronics, do not, as you can see, match gold and correspond to more modest Hadamard matrices. Copper, with its atomic weight not far from 63, is chemically active - its green oxides are well known.

Boron crystals under high magnification

FROM golden ratio boron is bound - the atomic mass among all other elements is closest to 10 (more precisely 10.8, the proximity of the atomic weight to odd numbers also affects). Boron is a fairly complex element. Bohr plays an intricate role in the history of life itself. The structure of the framework in its structures is much more complex than in diamond. The unique type of chemical bond that allows boron to absorb any impurity is very poorly understood, although a large number of scientists have already received Nobel Prizes for research related to it. The boron crystal is shaped like an icosahedron, with five triangles forming an apex.

The Riddle of Platinum. The fifth element is no doubt precious metals such as gold. Superstructure over Hadamard dimension 4 k, 1 large.

Stable isotope uranium 238

Recall, nevertheless, that Fermat numbers are rare (the nearest is 257). Native gold crystals have a shape close to a cube, but the pentagram also shines through. Its closest neighbor, platinum, a noble metal, is less than 4 at a distance from gold 197 in atomic weight. Platinum has an atomic weight not 193, but somewhat increased, 194 (the order of the Euler matrices). A trifle, but it brings her to the camp of slightly more aggressive elements. It is worth remembering, in connection with its inertness (it dissolves, perhaps, in aqua regia), platinum is used as an active catalyst for chemical processes.

Spongy platinum ignites hydrogen at room temperature. The character of platinum is not at all peaceful, iridium 192 (a mixture of isotopes 191 and 193) behaves more quietly. It is rather copper, but with the weight and character of gold.

There is no element with an atomic weight of 22 between neon 20 and sodium 23. Of course, atomic weights are an integral characteristic. But among isotopes, in turn, there is also a curious correlation of properties with the properties of numbers and the corresponding matrices of orthogonal bases. As a nuclear fuel, the isotope uranium 235 (the order of the Mersenne matrices) has the greatest application, in which a self-sustaining nuclear chain reaction is possible. In nature, this element is distributed in the stable form uranium 238 (the order of the Euler matrices). An element with an atomic weight of 13 is missing. As for chaos, the limited number of stable elements of the periodic table and the difficulty of finding high-order level matrices due to the barrier observed in the thirteenth-order matrices correlate.

Isotopes of chemical elements, an island of stability

Atom composition.

An atom consists of atomic nucleus and electronic shell.

The nucleus of an atom consists of protons ( p +) and neutrons ( n 0). Most hydrogen atoms have a single proton nucleus.

Number of protons N(p +) is equal to the nuclear charge ( Z) and the ordinal number of the element in the natural series of elements (and in the periodic table of elements).

N(p +) = Z

The sum of the number of neutrons N(n 0), denoted simply by the letter N, and the number of protons Z called massive number and denoted by the letter AND.

A = Z + N

The electron shell of an atom consists of electrons moving around the nucleus ( e -).

Number of electrons N(e -) in the electron shell of a neutral atom is equal to the number of protons Z at its core.

The mass of a proton is approximately equal to the mass of a neutron and is 1840 times the mass of an electron, so the mass of an atom is practically equal to the mass of a nucleus.

The shape of the atom is spherical. The radius of the nucleus is about 100,000 times smaller than the radius of the atom.

Chemical element - the kind of atoms (a set of atoms) with the same nuclear charge (with the same number of protons in the nucleus).

Isotope - a set of atoms of one element with the same number of neutrons in the nucleus (or the type of atoms with the same number of protons and the same number of neutrons in the nucleus).

Different isotopes differ from each other in the number of neutrons in the nuclei of their atoms.

The designation of a single atom or isotope: (E is the symbol of an element), for example:.

The structure of the electron shell of an atom

Atomic orbital - the state of an electron in an atom. Orbital symbol -. An electron cloud corresponds to each orbital.

Orbitals of real atoms in the ground (unexcited) state are of four types: s, p, d and f.

Electronic cloud - a part of the space in which an electron can be detected with a probability of 90 (or more) percent.

Note: sometimes the concepts of "atomic orbital" and "electron cloud" are not distinguished, calling both the "atomic orbital".

The electron shell of the atom is layered. Electronic layer formed by electron clouds of the same size. Orbitals of one layer form electronic ("energy") level, their energies are the same for the hydrogen atom, but different for other atoms.

Similar orbitals of the same level are grouped into electronic (energy) sublevels:
s- sublevel (consists of one s-orbital), symbol -.
p- sublevel (consists of three p
d- sublevel (consists of five d-orbitals), symbol -.
f- sublevel (consists of seven f-orbitals), symbol -.

The energies of the orbitals of one sublevel are the same.

When designating sublevels, the number of the layer (electronic layer) is added to the symbol of the sublevel, for example: 2 s, 3p, 5d means s-sublevel of the second level, p-sublevel of the third level, d-sublevel of the fifth level.

The total number of sublevels in one level is equal to the level number n... The total number of orbitals at one level is n 2. Accordingly, the total number of clouds in one layer is also n 2 .

Designations: - free orbital (without electrons), - orbital with an unpaired electron, - orbital with an electron pair (with two electrons).

The order of filling the orbitals of an atom with electrons is determined by three laws of nature (the formulations are given in a simplified manner):

1. The principle of least energy - electrons fill the orbitals in the order of increasing energy of the orbitals.

2. Pauli's principle - in one orbital there can be no more than two electrons.

3. Hund's rule - within the sublevel, electrons first fill free orbitals (one at a time), and only then form electron pairs.

The total number of electrons in the electronic level (or in the electron layer) is 2 n 2 .

The distribution of sublevels by energy is expressed as follows (in the order of increasing energy):

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p ...

This sequence is clearly expressed in an energy diagram:

The distribution of the electrons of an atom over levels, sublevels and orbitals (electronic configuration of an atom) can be depicted in the form of an electronic formula, an energy diagram, or, simply, in the form of a diagram of electronic layers ("electronic circuit").

Examples of the electronic structure of atoms:

Valence electrons - the electrons of the atom, which can take part in the formation of chemical bonds. For any atom, these are all external electrons plus those pre-external electrons, the energy of which is greater than that of the external ones. For example: a Ca atom has external electrons - 4 s 2, they are also valence; the Fe atom has external electrons - 4 s 2, but it has 3 d 6, therefore the iron atom has 8 valence electrons. The valence electronic formula of the calcium atom is 4 s 2, and the iron atom - 4 s 2 3d 6 .

Periodic table of chemical elements of D. I. Mendeleev
(natural system of chemical elements)

Periodic law of chemical elements (modern formulation): the properties of chemical elements, as well as simple and complex substances formed by them, are periodically dependent on the value of the charge from atomic nuclei.

Periodic system - graphic expression of the periodic law.

Natural range of chemical elements - a series of chemical elements, arranged according to the increasing number of protons in the nuclei of their atoms, or, which is the same, according to the increasing charges of the nuclei of these atoms. The ordinal number of an element in this row is equal to the number of protons in the nucleus of any atom of this element.

The table of chemical elements is constructed by "cutting" the natural series of chemical elements into periods (horizontal rows of the table) and groupings (vertical columns of the table) of elements with a similar electronic structure of atoms.

Depending on the method of combining elements into groups, the table may be long-period (elements with the same number and type of valence electrons are collected in groups) and short-period (elements with the same number of valence electrons are collected in groups).

The groups of the short-period table are divided into subgroups ( the main and side) that match the groups of the long-period table.

All atoms of elements of the same period have the same number of electronic layers equal to the period number.

The number of elements in periods: 2, 8, 8, 18, 18, 32, 32. Most of the elements of the eighth period are obtained artificially, the last elements of this period have not yet been synthesized. All periods, except the first, begin with an element that forms an alkali metal (Li, Na, K, etc.), and end with an element that forms a noble gas (He, Ne, Ar, Kr, etc.).

In the short-period table there are eight groups, each of which is divided into two subgroups (main and secondary), in the long-period table there are sixteen groups, which are numbered in Roman numerals with the letters A or B, for example: IA, IIIB, VIA, VIIB. Group IA of the long-period table corresponds to the main subgroup of the first group of the short-period table; group VIIB - a side subgroup of the seventh group: the rest are similar.

The characteristics of chemical elements change naturally in groups and periods.

In periods (with an increase in the serial number)

• the charge of the nucleus increases,
• the number of external electrons increases,
• the radius of atoms decreases,
• the bond strength of electrons with the nucleus (ionization energy) increases,
• electronegativity increases,
• the oxidizing properties of simple substances are enhanced ("non-metallic"),
• the reducing properties of simple substances ("metallicity") weaken,
• the basic character of hydroxides and corresponding oxides weakens,
• the acidic character of hydroxides and corresponding oxides increases.

In groups (with increasing serial number)

• the charge of the nucleus increases,
• the radius of atoms increases (only in A-groups),
• the bond strength of electrons with the nucleus decreases (ionization energy; only in A-groups),
• decreases electronegativity (only in A-groups),
• the oxidizing properties of simple substances weaken ("non-metallic"; only in A-groups),
• the reducing properties of simple substances are enhanced ("metallicity"; only in A-groups),
• the basic character of hydroxides and corresponding oxides increases (only in A-groups),
• the acidic nature of hydroxides and corresponding oxides weakens (only in A-groups),
• the stability of hydrogen compounds decreases (their reductive activity increases; only in A-groups).

Problems and tests on the topic "Topic 9." The structure of the atom. DI Mendeleev's Periodic Law and Periodic Table of Chemical Elements (PSKhE) "."

• Periodic law - Periodic law and the structure of atoms 8-9 grade
  You should know: the laws of filling orbitals with electrons (the principle of least energy, Pauli's principle, Hund's rule), the structure of the periodic table of elements.

  You should be able to: determine the composition of an atom by the position of an element in the periodic system, and, conversely, find an element in the periodic system, knowing its composition; to depict the structure diagram, the electronic configuration of an atom, ion, and, conversely, to determine the position of a chemical element in the PSCE according to the diagram and electronic configuration; to characterize the element and the substances formed by it by its position in the PSCE; determine changes in the radius of atoms, properties of chemical elements and the substances they form within one period and one main subgroup of the periodic system.

  Example 1. Determine the number of orbitals at the third electronic level. What are these orbitals?
  To determine the number of orbitals, we use the formula N orbitals \u003d n 2, where n - level number. N orbitals \u003d 3 2 \u003d 9. One 3 s-, three 3 p- and five 3 d-orbitals.

  Example 2. Determine which atom of which element has an electronic formula 1 s 2 2s 2 2p 6 3s 2 3p 1 .
  In order to determine which element it is, it is necessary to find out its serial number, which is equal to the total number of electrons of the atom. In this case: 2 + 2 + 6 + 2 + 1 \u003d 13. This is aluminum.

  After making sure that everything you need is learned, proceed to the assignments. We wish you every success.

  
  Recommended reading:
  • OS Gabrielyan and others. Chemistry 11 class. M., Bustard, 2002;
  • G. E. Rudzitis, F. G. Feldman. Chemistry 11 class. M., Education, 2001.

Bess Ruff is a PhD student from Florida working towards her PhD in geography. She received her MSc in Environmental Science and Management from the Bren School of Ecology and Management at the University of California, Santa Barbara in 2016.

The number of sources used in this article:. You will find a list of them at the bottom of the page.

If you find the periodic table difficult to understand, you are not alone! While it can be difficult to understand its principles, knowing how to work with it will help you in your science studies. First, study the structure of the table and what information can be learned from it about each chemical element. Then you can start exploring the properties of each item. And finally, using the periodic table, you can determine the number of neutrons in an atom of a particular chemical element.

Steps

Part 1

Table structure

The periodic table, or the periodic table of chemical elements, begins in the upper left corner and ends at the end of the last row of the table (in the lower right corner). Elements in the table are arranged from left to right in ascending order of their atomic number. The atomic number shows how many protons there are in one atom. In addition, as the atomic number increases, the atomic mass also increases. Thus, by the location of an element in the periodic table, you can determine its atomic mass.

1. As you can see, each next element contains one more proton than the previous element. This is obvious when you look at the atomic numbers. The atomic numbers increase by one as you move from left to right. Since the items are arranged in groups, some cells in the table are blank.

   • For example, the first row of the table contains hydrogen, which has atomic number 1, and helium, which has atomic number 2. However, they are located on opposite edges, since they belong to different groups.

2. Learn about groups that include elements with similar physical and chemical properties. The elements of each group are arranged in a corresponding vertical column. Typically, they are indicated by the same color, which helps to identify elements with similar physical and chemical properties and predict their behavior. All elements of one group or another have the same number of electrons on the outer shell.

   • Hydrogen can be attributed to both the alkali metal group and the halogen group. In some tables, it is indicated in both groups.
   • In most cases, groups are numbered from 1 to 18, with numbers at the top or bottom of the table. Numbers can be specified in Roman (for example, IA) or Arabic (for example, 1A or 1) numerals.
   • Moving along the column from top to bottom is said to be "viewing the group."

3. Find out why there are blank cells in the table. Elements are ordered not only according to their atomic number, but also according to groups (elements of one group have similar physical and chemical properties). This makes it easier to understand how this or that element behaves. However, as the atomic number grows, the elements that fall into the corresponding group are not always found, so there are empty cells in the table.

   • For example, the first 3 rows have empty cells, since transition metals are found only from atomic number 21.
   • Elements with atomic numbers 57 through 102 are classified as rare earth elements, and are usually listed in a separate subgroup in the lower right corner of the table.

4. Each row in the table represents a period. All elements of the same period have the same number of atomic orbitals, on which the electrons in the atoms are located. The number of orbitals corresponds to the number of the period. The table contains 7 rows, that is, 7 periods.

   • For example, the atoms of the elements of the first period have one orbital, and the atoms of the elements of the seventh period have 7 orbitals.
   • As a rule, periods are indicated by numbers from 1 to 7 on the left of the table.
   • Moving along the line from left to right is said to be "viewing a period."

5. Learn to distinguish between metals, metalloids and non-metals. You will better understand the properties of an element if you can determine what type it belongs to. For convenience, in most tables, metals, metalloids and non-metals are indicated by different colors. Metals are on the left and non-metals are on the right of the table. The metalloids are located between them.

   Part 2

   Element designations

   1. Each element is designated by one or two Latin letters. As a rule, the element symbol is shown in large letters in the center of the corresponding cell. A symbol is an abbreviated name for an element, which is the same in most languages. When doing experiments and working with chemical equations, symbols for the elements are commonly used, so it is helpful to remember them.

      • Typically, element symbols are an abbreviation of their Latin name, although for some, especially recently discovered elements, they are derived from a common name. For example, helium is denoted by the symbol He, which is close to the common name in most languages. At the same time, iron is referred to as Fe, which is an abbreviation of its Latin name.

   2. Pay attention to the full name of the element, if it is shown in the table. This "name" of the element is used in normal text. For example, "helium" and "carbon" are names for elements. Usually, although not always, the full names of the elements are listed under their chemical symbol.

      • Sometimes the names of elements are not indicated in the table and only their chemical symbols are given.

   3. Find the atomic number. Usually the atomic number of an element is located at the top of the corresponding cell, in the middle or in the corner. It can also appear below the symbol or element name. Elements have atomic numbers from 1 to 118.

      • The atomic number is always an integer.

   4. Remember that the atomic number corresponds to the number of protons in the atom. All atoms of an element contain the same number of protons. Unlike electrons, the number of protons in an element's atoms remains constant. Otherwise, another chemical element would have turned out!

      • The atomic number of an element can also determine the number of electrons and neutrons in an atom.

   5. Usually the number of electrons is equal to the number of protons. An exception is the case when the atom is ionized. Protons have a positive charge and electrons have a negative charge. Since atoms are usually neutral, they contain the same number of electrons and protons. However, an atom can capture electrons or lose them, in which case it will ionize.

      • Ions have an electrical charge. If there are more protons in an ion, then it has a positive charge, and in this case a plus sign is placed after the element symbol. If the ion contains more electrons, it has a negative charge, which is indicated by a minus sign.
      • The plus and minus signs are not used if the atom is not an ion.

The arrangement of electrons on energy shells or levels is recorded using electronic formulas of chemical elements. Electronic formulas or configurations help represent the atomic structure of an element.

Atom structure

The atoms of all elements are composed of a positively charged nucleus and negatively charged electrons, which are located around the nucleus.

Electrons are at different energy levels. The further the electron is from the nucleus, the more energy it possesses. The size of the energy level is determined by the size of the atomic orbital or orbital cloud. This is the space in which the electron moves.

Figure: 1. General structure of the atom.

Orbitals can have different geometric configurations:

• s-orbitals - spherical;
• p-, d and f-orbitals - dumbbell-shaped, lying in different planes.

At the first energy level of any atom there is always an s-orbital with two electrons (the exception is hydrogen). Starting from the second level, s- and p-orbitals are at the same level.

Figure: 2. s-, p-, d and f-orbitals.

Orbitals exist regardless of the presence of electrons on them and can be filled or vacant.

Formula writing

The electronic configurations of atoms of chemical elements are written according to the following principles:

• each energy level corresponds to a sequential number denoted by an Arabic numeral;
• the number is followed by a letter representing the orbital;
• a superscript is written above the letter, corresponding to the number of electrons in the orbital.

Recording examples: