EntranceEnergy level, sublevel, orbital, types of orbitals. Energy levels and sublevels How to write energy levels in chemistry
Energy level– the set of all orbitals with the same value of n. The number of levels at which electrons are located in the ground state of the atom coincides with the number of the period in which the element is located: 1, 2, 3 ...
Energy sublevel– a set of energy states of an electron in an atom, characterized by the same values of quantum numbers n and l. Sublevels are designated: s, p, d, f...
I energy level – 1 sublevel
Energy level II – 2 sublevels
III energy level – 3 sublevels
Orbital– region of space where the electron is most likely to reside in an electron. Field of the atomic nucleus. Orbitals are characterized by quantum numbers.
Types of orbitals:
Pauli's principle and its corollary:
There cannot be 2 electrons in an atom that would have the same set of all 4 quantum numbers.
A consequence of this principle is the fact that all orbitals in an atom are sequentially filled.
Principle of least energy:
The principle determines the sequence of filling orbitals with electrons; in the ground state of the atom, each electron is located so that its energy is minimal.
The ground state is the most stable state of an atom, in which electrons occupy orbitals with the lowest energy.
Hund's Rule:
In the ground state, an atom has the maximum possible number of unpaired electrons within a certain sublevel. For example, if there are three electrons in the 2p sublevel. Then they must be in 3 different orbitals:
In this case, the total spin is maximum and equal to 3/2.
Electronic formulas (configurations) of atoms:
Electronic configuration is a formula for the arrangement of electrons in different electron shells of an atom of a chemical element or molecule.
For light orbitals, any period begins with the s-orbital and ends with the p-orbital (except for the 1st). If several heavy orbitals are present, then the one whose p i is smaller is filled first.
The sequence of filling orbitals with electrons is determined by the principle of least energy: in the ground state of the atom, each electron is located so that its energy is minimal.
1s<2s<2p<3s<3p<4s<3d<4p<5s<4d<5p<6s<4f<5d<6p<7s<5f<6d<7p
Nchar = n i + l i
TICKET
The periodic law of chemical elements and its physical meaning:
The periodic law, formed by Mendeleev in 1869, is as follows:
The properties of simple bodies, as well as the forms and properties of compounds of elements, are periodically dependent on the atomic weights of the elements.
Thus, the change in the properties of chemical elements as their atomic mass increases does not occur continuously in the same direction, but has a periodic character.
The physical meaning of the periodic law is that with a consistent increase in the charges of the nuclei of the principal quantum number, similar valence electronic structures of atoms are periodically repeated, and as a result, the chemical properties of the elements are periodically repeated
Periodic table of elements:
The periodic table of elements is a classification of chemical elements, graphically depicted in the form of a periodic table. It consists of seven periods (ten side by side) and eight groups.
In this system, Mendeleev divided all elements into periods and placed one period under another so that elements similar in properties and type of compounds formed were located under each other.
Multi-electron atom
| Energy level n | Energy sublevel | Orbital designation | Number of orbitals n | Number of electrons 2n | |
| l | type of orbital | ||||
| s | 1s | ||||
| 2 | s p | 2s 2p | 3 4 | 2 8 | |
| 3 | s p d | 3s 3p 3d | 3 9 | 6 18 | |
| 4 | s p d f | 4s 4p 4d 4f | 3 16 | 6 32 |
Magnetic quantum number m l within this sublevel ( n, l = const) accepts all integer values from + l before - l, including zero. For the s-sublevel ( n = const, l = 0) only one value is possible m l = 0, which means that the s-sublevel of any (from the first to the seventh) energy level contains one s-AO.
For the p-sublevel ( n> 1, l = 1) m l can take three values +1, 0, -1, therefore, the p-sublevel of any (from the second to the seventh) energy level contains three p-AOs.
For d-sublevel ( n> 2, l = 2) m l has five values +2, +1, 0, -1, -2 and, as a consequence, d- sublevel of any (from the third to the seventh) energy level necessarily contains five d- JSC.
Likewise, for each f- sublevel ( n> 3, l = 3) m has seven values +3, +2, +1, 0, -1, -2, -3 and therefore any f- sublevel contains seven f- JSC.
Thus, Each atomic orbital is uniquely determined by three quantum numbers - the main n, orbital l and magnetic m l.
At n = const all values related to a given energy level are strictly defined l, and when l = const – all values related to a given energy sublevel m l.
Because each orbital can be filled with a maximum of two electrons, the number of electrons that can be accommodated in each energy level and sublevel is twice the number of orbitals in that level or sublevel. Since electrons located in the same atomic orbital have the same quantum numbers n, l And m l, then for two electrons in one orbital the fourth is used, spin quantum number s, which is determined by the spin of the electron.
According to the Pauli principle, it can be stated that Each electron in an atom is uniquely characterized by its own set of four quantum numbers - the main n, orbital l, magnetic m and spin s.
The population of energy levels, sublevels and atomic orbitals by electrons is subject to the following rule (principle of minimum energy): in an unexcited state, all electrons have the lowest energy.
This means that each of the electrons filling the shell of an atom occupies such an orbital that the atom as a whole has a minimum energy. Consistent quantum increase in the energy of sublevels occurs in the following order:
1s – 2s – 2p – 3s – 3p – 4s – 3d – 4p – 5s-…..
The filling of atomic orbitals within one energy sublevel occurs in accordance with the rule formulated by the German physicist F. Hund (1927).
Hund's rule: atomic orbitals belonging to the same sublevel are each filled first with one electron, and then they are filled with second electrons.
Hund's rule is also called the principle of maximum multiplicity, i.e. the maximum possible parallel direction of the spins of electrons of one energy sublevel.
A free atom can have no more than eight electrons at its highest energy level.
Electrons located at the highest energy level of an atom (in the outer electron layer) are called external; The number of outer electrons in an atom of any element is never more than eight. For many elements, it is the number of external electrons (with filled internal sublevels) that largely determines their chemical properties. For other electrons whose atoms have an unfilled internal sublevel, for example 3 d- sublevel of atoms of elements such as Sc, Ti, Cr, Mn, etc., chemical properties depend on the number of both internal and external electrons. All these electrons are called valence; in abbreviated electronic formulas of atoms they are written after the symbol of the atomic skeleton, that is, after the expression in square brackets.
Related information.
Energy sublevels - section Chemistry, Fundamentals of inorganic chemistry Orbital Quantum Number L Form...
According to the limits of changes in the orbital quantum number from 0 to (n-1), in each energy level a strictly limited number of sublevels is possible, namely: the number of sublevels is equal to the level number.
The combination of principal (n) and orbital (l) quantum numbers completely characterizes the energy of the electron. The energy reserve of an electron is reflected by the sum (n+l).
For example, electrons of the 3d sublevel have higher energy than electrons of the 4s sublevel:
The order of filling levels and sublevels in an atom with electrons is determined rule V.M. Klechkovsky: filling of the electronic levels of the atom occurs sequentially in order of increasing sum (n+1).
In accordance with this, the real energy scale of sublevels has been determined, according to which the electron shells of all atoms are constructed:
1s ï 2s2p ï 3s3p ï 4s3d4p ï 5s4d5p ï 6s4f5d6p ï 7s5f6d…
3. Magnetic quantum number (m l) characterizes the direction of the electron cloud (orbital) in space.
The more complex the shape of the electron cloud (i.e., the higher the value of l), the more variations in the orientation of a given cloud in space and the more individual energy states of the electron exist, characterized by a certain value of the magnetic quantum number.
Mathematically m l accepts integer values from -1 to +1, including 0, i.e. total (21+1) values.
Let us denote each individual atomic orbital in space as an energy cell ð, then the number of such cells in sublevels will be:
| Sublevel | Possible values of m l | Number of individual energy states (orbitals, cells) in a sublevel | |
| s (l=0) | one | ||
| p (l=1) | -1, 0, +1 | three | |
| d (l=2) | -2, -1, 0, +1, +2 | five |  |
| f (l=3) | -3, -2, -1, 0, +1, +2, +3 | seven |  |
For example, a spherical s-orbital is uniquely directed in space. The dumbbell orbitals of each p-sublevel are oriented along three coordinate axes
4. Spin quantum number m s characterizes the electron’s own rotation around its axis and takes only two values:
p- sublevel + 1/2 and – 1/2, depending on the direction of rotation in one direction or the other. According to the Pauli principle, no more than 2 electrons with oppositely directed (antiparallel) spins can be located in one orbital:
Such electrons are called paired. An unpaired electron is schematically represented by a single arrow:.
Knowing the capacity of one orbital (2 electrons) and the number of energy states in a sublevel (m s), we can determine the number of electrons in sublevels:
You can write the result differently: s 2 p 6 d 10 f 14.
These numbers must be remembered well in order to correctly write the electronic formulas of the atom.
So, four quantum numbers - n, l, m l, m s - completely determine the state of each electron in the atom. All electrons in an atom with the same value of n constitute an energy level, with the same values of n and l - an energy sublevel, with the same values of n, l and m l– a separate atomic orbital (quantum cell). Electrons in one orbital have different spins.
Taking into account the values of all four quantum numbers, we determine the maximum number of electrons in energy levels (electronic layers):
Large numbers of electrons (18.32) are contained only in the deep-lying electronic layers of atoms; the outer electron layer can contain from 1 (for hydrogen and alkali metals) to 8 electrons (inert gases).
It is important to remember that the filling of electron shells with electrons occurs according to principle of least energy: sublevels with the minimum energy value are filled first, then those with higher values. This sequence corresponds to the energy scale of V.M. sublevels. Klechkovsky.
The electronic structure of an atom is displayed by electronic formulas, which indicate energy levels, sublevels and the number of electrons in sublevels.
For example, the hydrogen atom 1 H has only 1 electron, which is located in the first layer from the nucleus on the s-sublevel; the electronic formula of the hydrogen atom is 1s 1.
The lithium atom 3 Li has only 3 electrons, 2 of which are in the s-sublevel of the first layer, and 1 is placed in the second layer, which also begins with the s-sublevel. The electronic formula of the lithium atom is 1s 2 2s 1.
The 15P phosphorus atom has 15 electrons arranged in three electron layers. Remembering that the s-sublevel contains no more than 2 electrons, and the p-sublevel contains no more than 6, we gradually place all the electrons in the sublevels and compose the electronic formula of the phosphorus atom: 1s 2 2s 2 2p 6 3s 2 3p 3.
When compiling the electronic formula of the manganese atom 25 Mn, it is necessary to take into account the sequence of increasing energy of sublevels: 1s2s2p3s3p4s3d…
We gradually distribute all 25 electrons of Mn: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5.
The final electronic formula of the manganese atom (taking into account the distance of electrons from the nucleus) looks like this:
| 1s 2 | 2s 2 2p 6 | 3s 2 3p 6 3d 5 | 4s 2 |
The electronic formula of manganese fully corresponds to its position in the periodic table: the number of electronic layers (energy levels) - 4 is equal to the period number; there are 2 electrons in the outer layer, the penultimate layer is not complete, which is typical for metals of secondary subgroups; the total number of mobile valence electrons (3d 5 4s 2) – 7 is equal to the group number.
Depending on which of the energy sublevels in the atom -s-, p-, d- or f- is built up last, all chemical elements are divided into electronic families: s-elements(H, He, alkali metals, metals of the main subgroup of the 2nd group of the periodic table); p-elements(elements of the main subgroups 3, 4, 5, 6, 7, 8 of the periodic system); d-elements(all metals of secondary subgroups); f-elements(lanthanides and actinides).
The electronic structures of atoms are a deep theoretical basis for the structure of the periodic system; the length of the periods (i.e., the number of elements in the periods) directly follows from the capacity of the electronic layers and the sequence of increasing energy of the sublevels:
Each period begins with an s-element with the structure of the outer layer s 1 (alkali metal) and ends with a p-element with the structure of the outer layer ...s 2 p 6 (inert gas). The first period contains only two s-elements (H and He), the second and third minor periods each contain two s-elements and six p-elements. In the 4th and 5th major periods, 10 d-elements – transition metals, separated into secondary subgroups – “wedge” between the s- and p-elements. In periods VI and VII, another 14 f-elements are added to a similar structure, with properties similar to lanthanum and actinium, respectively, and identified as subgroups of lanthanides and actinides.
When studying the electronic structures of atoms, pay attention to their graphical representation, for example:
13 Al 1s 2 2s 2 2p 6 3s 2 3p 1
Both image options are used: a) and b):
For the correct arrangement of electrons in orbitals, you need to know Hund's rule: electrons in a sublevel are arranged so that their total spin is maximum. In other words, electrons first occupy all free cells of a given sublevel one by one.
For example, if it is necessary to place three p-electrons (p 3) in the p-sublevel, which always has three orbitals, then of the two possible options, the first option meets Hund’s rule:
As an example, consider a graphical electronic diagram of a carbon atom:
6 C 1s 2 2s 2 2p 2
The number of unpaired electrons in an atom is a very important characteristic. According to the covalent bond theory, only unpaired electrons can form chemical bonds and determine the valence capabilities of an atom.
If there are free energy states (unoccupied orbitals) in the sublevel, the atom, when excited, “steams”, separates paired electrons, and its valence capabilities increase:
6 C 1s 2 2s 2 2p 3
Carbon in the normal state is 2-valent, in the excited state it is 4-valent. The fluorine atom does not have the potential for excitation (since all orbitals of the outer electron layer are occupied), therefore fluorine in its compounds is monovalent.
Example 1. What are quantum numbers? What values can they take?
Solution. The movement of an electron in an atom is probabilistic. The circumnuclear space, in which with the highest probability (0.9-0.95) an electron can be located, is called an atomic orbital (AO). An atomic orbital, like any geometric figure, is characterized by three parameters (coordinates), called quantum numbers (n, l, m l). Quantum numbers do not take on any, but certain, discrete (discontinuous) values. Adjacent values of quantum numbers differ by one. Quantum numbers determine the size (n), shape (l) and orientation (m l) of an atomic orbital in space. Occupying one or another atomic orbital, an electron forms an electron cloud, which can have different shapes for electrons of the same atom (Fig. 1). The shapes of electron clouds are similar to AO. They are also called electron or atomic orbitals. An electron cloud is characterized by four numbers (n, l, m 1 and m 5).
What will we do with the received material:
If this material was useful to you, you can save it to your page on social networks:
| Tweet |
All topics in this section:
Basic laws and concepts of chemistry
The branch of chemistry that considers the quantitative composition of substances and quantitative relationships (mass, volume) between reacting substances is called stoichiometry. According to this,
Chemical symbolism
Modern symbols for chemical elements were introduced in 1813 by Berzelius. Elements are designated by the initial letters of their Latin names. For example, oxygen (Oxygenium) is denoted by the letter O, ce
Latin roots of some elements
Ordinal number in the table of the periodic system Symbol Russian name Latin root
Group names of elements
Name of the group of elements Elements of the group Noble gases He, Ne, Ar, Kr, Xe, Rn Halogens
Names of the most commonly used acids and acid residues
Acid formulas Name of acid Formula of acid residue Name of acid residue Oxygen acids
Obtaining acids
1 . Interaction of acid oxides (most) with water: SO3 + H2O=H2SO4; N2O5 + H2
Nomenclature of inorganic compounds (according to IUPAC rules)
IUPAC is the International Union of Pure and Applied Chemistry. The 1970 IUPAC Rules are an international model that creates nomenclature rules for chemical compounds in the language of coo
First models of the atom
In 1897, J. Thomson (England) discovered the electron, and in 1909. R. Mulliken determined its charge, which is equal to 1.6 10-19 C. The electron mass is 9.11 10-28 g. V
Atomic spectra
When heated, a substance emits rays (radiation). If radiation has one wavelength, then it is called monochromatic. In most cases, the radiation is characterized by several
Quanta and the Bohr model
In 1900, M. Planck (Germany) suggested that substances absorb and emit energy in discrete portions, which he called quanta. The energy of the quantum E is proportional to the radiation frequency (ko
The dual nature of the electron
In 1905, A. Einstein predicted that any radiation is a stream of energy quanta, called photons. From Einstein's theory it follows that light has a dual (particle-wave)
Values of quantum numbers and the maximum number of electrons at quantum levels and sublevels
Quantum Magnetic quantum number ml Number of quantum states (orbitals) Maximum number of electrons
Isotopes of hydrogen
Isotope Nuclear charge (ordinal number) Number of electrons Atomic mass Number of neutrons N=A-Z Protium
Periodic table of elements D.I. Mendeleev and the electronic structure of atoms
Let us consider the relationship between the position of an element in the periodic table and the electronic structure of its atoms. Each subsequent element of the periodic table has one more electron than the previous one.
Electronic configurations of elements of the first two periods
Atomic number Element Electronic configurations Atomic number Element Electronic configurations
Electronic configurations of elements
Period Ordinal number Element Electronic configuration Period Ordinal number Element
Periodic properties of elements
Since the electronic structure of elements changes periodically, the properties of elements determined by their electronic structure, such as ionization energy,
Electronegativity of elements according to Pauling
H 2.1 &
Oxidation states of arsenic, selenium, bromine
Element Oxidation state Compounds highest lowest
Abbreviated and complete nuclear reaction equations
Abbreviated equations Full equations 27Al(p,
Definition of a chemical bond
The properties of substances depend on their composition, structure, and the type of chemical bond between the atoms in the substance. A chemical bond is electrical in nature. By chemical bond we mean the type
Ionic bond
When any molecule is formed, the atoms of this molecule “bond” with each other. The reason molecules form is because electrostatic forces act between the atoms in the molecule. Obrazova
Covalent bond
A chemical bond made by overlapping electron clouds of interacting atoms is called a covalent bond. 4.3.1. Non-polar kovale
Valence bond method (MVS, BC)
For a deep understanding of the essence of a covalent bond, the nature of the distribution of electron density in a molecule, the principles of constructing molecules of simple and complex substances, the method of valence bonds is required
Molecular orbital method (MMO, MO)
Chronologically, the MO method appeared later than the BC method, since questions remained in the theory of covalent bonds that could not be explained by the BC method. Let's point out some of them. How
Basic provisions of IMO, MO
1. In a molecule, all electrons are shared. The molecule itself is a single whole, a collection of nuclei and electrons. 2. In a molecule, each electron corresponds to a molecular orbital, like
Orbital hybridization and spatial configuration of molecules
Type of molecule Initial orbitals of atom A Type of hybridization Number of hybrid orbitals of atom A Pr
Metal connection
The name itself says that we will talk about the internal structure of metals. The atoms of most metals contain a small number of electrons at the outer energy level. So, one electron each
Hydrogen bond
A hydrogen bond is a kind of chemical bond. It occurs between molecules that contain hydrogen and a strongly electronegative element. These elements are fluorine, oxygen
Interactions between molecules
When molecules come together, attraction appears, which causes the appearance of a condensed state of matter. The main types of interaction between molecules include van der Waals forces, in which
Contribution of individual components to the energy of intermolecular interaction
Substance Electric dipole moment, D Polarizability, m3∙1030 Interaction energy, kJ/m
General concepts
When chemical reactions occur, the energy state of the system in which the reaction occurs changes. The state of the system is characterized by thermodynamic parameters (p, T, s, etc.)
Internal energy. First law of thermodynamics
During chemical reactions, profound qualitative changes occur in the system, bonds in the starting substances are broken and new bonds appear in the final products. These changes are accompanied by absorption
Enthalpy of the system. Thermal effects of chemical reactions
Heat Q and work A are not state functions, because they serve as forms of energy transfer and are associated with the process, and not with the state of the system. In chemical reactions A is work against external
Thermochemical calculations
Thermochemical calculations are based on Hess's law, which allows one to calculate the enthalpy of a chemical reaction: the thermal effect of the reaction depends only on the nature and physical state of the starting substances
Standard heats (enthalpies) of formation
some substances Substance
Chemical affinity. Entropy of chemical reactions. Gibbs energy
Reactions can occur spontaneously, accompanied not only by the release, but also by the absorption of heat. A reaction that occurs at a given temperature and releases heat at a different temperature
Second and third laws of thermodynamics
For systems that do not exchange either energy or matter with the environment (isolated systems), the second law of thermodynamics has the following formulation: in isolated systems the very
The concept of the rate of chemical reactions
The rate of a chemical reaction is the number of elementary reaction events occurring per unit time per unit volume (in the case of homogeneous reactions) or per unit interface surface (in
Dependence of the reaction rate on the concentration of reagents
In order for an atom and molecules to react, they must collide with each other, since the forces of chemical interaction act only over a very short distance. The more molecules there are
Effect of temperature on reaction rate
The dependence of the reaction rate on temperature is determined by Van't Hoff's rule, according to which, with every 10-degree increase in temperature, the rate of most reactions increases by 2-
Activation energy
The rapid change in reaction rate with temperature changes is explained by activation theory. Why does heating cause such a significant acceleration of chemical transformations? To answer this question you need
Concept of catalysis and catalysts
Catalysis is the change in the rate of chemical reactions in the presence of substances - catalysts. Catalysts are substances that change the rate of a reaction by participating in a chemical intermediate.
Chemical balance. Le Chatelier's principle
Reactions that proceed in one direction and go to completion are called irreversible. There aren't many of them. Most reactions are reversible, i.e. they flow in opposite directions
Methods of expressing the concentration of solutions
The concentration of a solution is the content of a dissolved substance in a certain mass or known volume of a solution or solvent. There are mass, molar (molar-volume), mo
Colligative properties of solutions
Colligative properties are properties of solutions that depend on concentration and are practically independent of the nature of the dissolved substances. They are also called general (collective). T
Electrolyte solutions
Examples of electrolyte solutions include solutions of alkalis, salts and inorganic acids in water, solutions of a number of salts and liquid ammonia and some organic solvents, such as acetonite
In solutions at 298 K
Concentration, mol/1000g Н2О Activity coefficient for electrolytes NaCl KCl NaOH KOH
Hydrolysis of salts
Chemical exchange interaction of dissolved salt ions with water, leading to the formation of weakly dissociating products (molecules of weak acids or bases, acidic anions or basic cations
Constants and degrees of dissociation of some weak electrolytes
Electrolytes Formula Numerical values of dissociation constants Degree of dissociation in 0.1 n. solution, % Nitrous acids
Processes
Redox reactions are reactions that are accompanied by a change in the oxidation state of the atoms that make up the reacting substances.
Valence and oxidation states of atoms in some compounds
Molecule Bond ionicity, % Atom Covalentity Electrovalency Valency: v = ve
Redox reactions
Let us consider the basic principles of the theory of redox reactions. 1. Oxidation is the process of losing electrons by an atom, molecule or ion. The degree of oxidation in this case
The most important reducing and oxidizing agents
Reducing agents Oxidizing agents Metals, hydrogen, coal Carbon monoxide (II) CO Hydrogen sulfide H2S, sodium sulfide Na2S, selenium oxide
Drawing up equations for redox reactions
To compile equations of redox reactions and determine coefficients, two methods are used: the electron balance method and the ion-electronic method (half-reaction method).
Determination of complex compounds
Compounds such as oxides, acids, bases, and salts are formed from atoms as a result of the formation of a chemical bond between them. These are ordinary connections, or connections of the first order
Ligands
Ligands include simple anions, such as F-, CI-, Br-, I-, S2-, complex anions, for example CN–, NCS–, NO
Nomenclature of complex compounds
The name of the complex cation is written in one word, starting with the name of the negative ligand with the addition of the letter “o”, then the neutral molecules and the central atom are given with the indication
Dissociation of complex compounds
Complex compounds - non-electrolytes in aqueous solutions do not undergo dissociation. They lack the outer sphere of the complex, for example: , )