The nature of the metallic bond. The structure of metal crystals.
1. With. 71–73; 2. With. 143–147; 4. With. 90–93; 8. With. 138–144; 3. With. 130–132.
Ionic chemical bond called the bond that is formed between cations and anions as a result of their electrostatic interaction. An ionic bond can be viewed as the limiting case of a covalent polar bond formed by atoms with very different electronegativity values.
When an ionic bond is formed, a significant shift of the common pair of electrons to a more electronegative atom occurs, which thus acquires a negative charge and turns into an anion. Another atom, having lost its electron, forms a cation. An ionic bond is formed only between atomic particles of such elements that differ greatly in their electronegativity (Δχ ≥ 1.9).
Ionic bond is characterized non-directionality in space and insatiability. The electric charges of the ions determine their attraction and repulsion and determine the stoichiometric composition of the compound.
In general, an ionic compound is a giant association of ions with opposite charges. Therefore, the chemical formulas of ionic compounds reflect only the simplest ratio between the numbers of atomic particles that form such associations.
Metal connection -ininteraction that holds atomic particles of metals in crystals.
The nature of a metallic bond is similar to a covalent bond: both types of bonds are based on the socialization of valence electrons. However, in the case of a covalent bond, the valence electrons of only two neighboring atoms are shared, while in the formation of a metallic bond, all atoms take part in the sharing of these electrons at once. The low ionization energies of metals make it easy for valence electrons to detach from atoms and move throughout the entire volume of the crystal. Due to the free movement of electrons, metals have high electrical and thermal conductivity.
Thus, a relatively small number of electrons ensures the binding of all atoms in a metal crystal. A bond of this type, in contrast to a covalent bond, is non-localized and non-directional.
7. Intermolecular interaction . Orientation, induction and dispersion interaction of molecules. Dependence of the energy of intermolecular interaction on the value of the dipole moment, polarizability and size of molecules. Energy of intermolecular interaction and aggregate state of substances. The nature of the change in the boiling and melting points of simple substances and molecular compounds of p-elements of groups IV-VII.
1. With. 73–75; 2. With. 149–151; 4. With. 93–95; 8. With. 144–146; 11. With. 139–140.
Although the molecules as a whole are electrically neutral, intermolecular interactions take place between them.
The cohesive forces acting between single molecules and leading first to the formation of a molecular liquid, and then molecular crystals, are calledintermolecular forces , or van der Waals forces .
Intermolecular interaction, like a chemical bond, has electrostatic nature, but, unlike the latter, is very weak; manifests itself at much greater distances and is characterized by the absence of satiety.
There are three types of intermolecular interaction. The first type is orientationalinteraction polar molecules. When approaching, the polar molecules orient themselves relative to each other in accordance with the signs of the charges at the ends of the dipoles. The more polar the molecules, the stronger the orientation interaction. Its energy is determined primarily by the magnitude of the electric moments of the dipoles of molecules (ie, their polarity).
Inductive interaction – it is an electrostatic interaction between polar and non-polar molecules.
In a non-polar molecule, under the influence of the electric field of a polar molecule, an "induced" (induced) dipole arises, which is attracted to the constant dipole of the polar molecule. The energy of the inductive interaction is determined by the electric moment of the dipole of the polar molecule and the polarizability of the nonpolar molecule.
Dispersion interaction arises as a result of mutual attraction of the so-called instantaneous dipoles. Dipoles of this type arise in non-polar molecules at any time due to the mismatch between the electrical centers of gravity of the electron cloud and nuclei, caused by their independent vibrations.
The relative value of the contribution of individual components to the total energy of intermolecular interaction depends on two main electrostatic characteristics of the molecule - its polarity and polarizability, which, in turn, are determined by the size and structure of the molecule.
8. hydrogen bond . Mechanism of formation and nature of the hydrogen bond. Comparison of hydrogen bond energy with chemical bond energy and intermolecular interaction energy. Intermolecular and intramolecular hydrogen bonds. The nature of the change in the melting and boiling points of hydrides of p-elements of IV-VII groups. Importance of hydrogen bonds for natural objects. Anomalous properties of water.
1. With. 75–77; 2. With. 147–149; 4. With. 95–96; 11. With. 140–143.
One of the varieties of intermolecular interaction is hydrogen bond . It is carried out between the positively polarized hydrogen atom of one molecule and the negatively polarized X atom of another molecule:
Х δ- ─Н δ+ Х δ- ─Н δ+ ,
where X is an atom of one of the most electronegative elements - F, O or N, and the symbol is a symbol for a hydrogen bond.
The formation of a hydrogen bond is primarily due to the fact that the hydrogen atom has only one electron, which, when a polar covalent bond is formed with the X atom, is shifted towards it. A high positive charge arises on the hydrogen atom, which, combined with the absence of internal electron layers in the hydrogen atom, allows another atom to approach it up to distances close to the lengths of covalent bonds.
Thus, a hydrogen bond is formed as a result of the interaction of dipoles. However, unlike the usual dipole-dipole interaction, the mechanism of hydrogen bonding is also due to the donor-acceptor interaction, where the electron pair donor is the X atom of one molecule, and the acceptor is the hydrogen atom of another.
The hydrogen bond has the properties of directionality and saturation. The presence of a hydrogen bond significantly affects the physical properties of substances. For example, the melting and boiling points of HF, H 2 O and NH 3 are higher than those of hydrides of other elements of the same groups. The reason for the anomalous behavior is the presence of hydrogen bonds, the breaking of which requires additional energy.
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Lesson Objectives:
- To form the concept of chemical bonds using the example of an ionic bond. To achieve an understanding of the formation of an ionic bond as an extreme case of a polar one.
- During the lesson, ensure the assimilation of the following basic concepts: ions (cation, anion), ionic bond.
- To develop the mental activity of students through the creation of a problem situation when studying new material.
Tasks:
- learn to recognize the types of chemical bonds;
- repeat the structure of the atom;
- to investigate the mechanism of formation of ionic chemical bond;
- teach how to draw up formation schemes and electronic formulas of ionic compounds, reaction equations with the designation of the transition of electrons.
Equipment Keywords: computer, projector, multimedia resource, periodic system of chemical elements D.I. Mendeleev, table "Ionic bond".
Lesson type: Formation of new knowledge.
Type of lesson: multimedia lesson.
X one lesson
I.Organizing time.
II . Checking homework.
Teacher: How can atoms take on stable electronic configurations? What are the ways of forming a covalent bond?
Student: Polar and non-polar covalent bonds are formed by the exchange mechanism. The exchange mechanism includes cases when one electron is involved in the formation of an electron pair from each atom. For example, hydrogen: (slide 2)
The bond arises due to the formation of a common electron pair due to the union of unpaired electrons. Each atom has one s-electron. The H atoms are equivalent and the pairs equally belong to both atoms. Therefore, the formation of common electron pairs (overlapping p-electron clouds) occurs during the formation of the F 2 molecule. (slide 3)
H entry · means that the hydrogen atom has 1 electron on the outer electron layer. The record shows that there are 7 electrons on the outer electron layer of the fluorine atom.
During the formation of the N 2 molecule. 3 common electron pairs are formed. The p-orbitals overlap. (slide 4)
The bond is called non-polar.
Teacher: We have now considered cases when molecules of a simple substance are formed. But there are many substances around us, a complex structure. Let's take a hydrogen fluoride molecule. How does the formation of a connection take place in this case?
Student: When a hydrogen fluoride molecule is formed, the orbital of the s-electron of hydrogen and the orbital of the p-electron of fluorine H-F overlap. (slide 5)
The bonding electron pair is shifted to the fluorine atom, resulting in the formation dipole. Connection called polar.
III. Knowledge update.
Teacher: A chemical bond arises as a result of changes that occur with the outer electron shells of the connecting atoms. This is possible because the outer electron layers are not complete in elements other than inert gases. The chemical bond is explained by the desire of atoms to acquire a stable electronic configuration, similar to the configuration of the "nearest" inert gas to them.
Teacher: Write down a diagram of the electronic structure of the sodium atom (at the blackboard). (slide 6)
Student: To achieve the stability of the electron shell, the sodium atom must either give up one electron or accept seven. Sodium will easily give up its electron far from the nucleus and weakly bound to it.
Teacher: Make a diagram of the recoil of an electron.
Na° - 1ē → Na+ = Ne
Teacher: Write down a diagram of the electronic structure of the fluorine atom (at the blackboard).
Teacher: How to achieve the completion of the filling of the electronic layer?
Student: To achieve the stability of the electron shell, the fluorine atom must either give up seven electrons or accept one. It is energetically more favorable for fluorine to accept an electron.
Teacher: Make a scheme for receiving an electron.
F° + 1ē → F- = Ne
IV. Learning new material.
The teacher addresses a question to the class in which the task of the lesson is set:
Are there other options in which atoms can take on stable electronic configurations? What are the ways of formation of such bonds?
Today we will consider one of the types of bonds - ionic bonds. Let us compare the structure of the electron shells of the already named atoms and inert gases.
Conversation with the class.
Teacher: What charge did the sodium and fluorine atoms have before the reaction?
Student: The atoms of sodium and fluorine are electrically neutral, because. the charges of their nuclei are balanced by electrons revolving around the nucleus.
Teacher: What happens between atoms when giving and receiving electrons?
Student: Atoms acquire charges.
The teacher gives explanations: In the formula of an ion, its charge is additionally recorded. To do this, use the superscript. In it, a number indicates the amount of charge (they do not write a unit), and then a sign (plus or minus). For example, a Sodium ion with a charge of +1 has the formula Na + (read "sodium plus"), a Fluorine ion with a charge of -1 - F - ("fluorine minus"), a hydroxide ion with a charge of -1 - OH - (" o-ash-minus"), a carbonate ion with a charge of -2 - CO 3 2- ("tse-o-three-two-minus").
In the formulas of ionic compounds, first write down, without indicating the charges, positively charged ions, and then - negatively charged. If the formula is correct, then the sum of the charges of all ions in it is equal to zero.
positively charged ion called a cation, and a negatively charged ion-anion.
Teacher: We write the definition in workbooks:
And he is a charged particle into which an atom turns into as a result of receiving or giving off electrons.
Teacher: How to determine the charge of the calcium ion Ca 2+?
Student: An ion is an electrically charged particle formed as a result of the loss or gain of one or more electrons by an atom. Calcium has two electrons in the last electronic level, the ionization of a calcium atom occurs when two electrons are given away. Ca 2+ is a doubly charged cation.
Teacher: What happens to the radii of these ions?
During the transition electrically neutral atom into an ionic state, the particle size changes greatly. An atom, giving up its valence electrons, turns into a more compact particle - a cation. For example, during the transition of a sodium atom to the Na+ cation, which, as indicated above, has a neon structure, the radius of the particle is greatly reduced. The radius of an anion is always greater than the radius of the corresponding electrically neutral atom.
Teacher: What happens to oppositely charged particles?
Student: Oppositely charged sodium and fluorine ions, resulting from the transition of an electron from a sodium atom to a fluorine atom, are mutually attracted and form sodium fluoride. (slide 7)
Na + + F - = NaF
The scheme of formation of ions that we have considered shows how a chemical bond is formed between the sodium atom and the fluorine atom, which is called ionic.
Ionic bond- a chemical bond formed by the electrostatic attraction of oppositely charged ions to each other.
The compounds that form in this case are called ionic compounds.
V. Consolidation of new material.
Tasks to consolidate knowledge and skills
1. Compare the structure of the electron shells of the calcium atom and the calcium cation, the chlorine atom and the chloride anion:
Comment on the formation of an ionic bond in calcium chloride:
2. To complete this task, you need to divide into groups of 3-4 people. Each member of the group considers one example and presents the results to the whole group.
Students response:
1. Calcium is an element of the main subgroup of group II, a metal. It is easier for its atom to donate two outer electrons than to accept the missing six:
2. Chlorine is an element of the main subgroup of group VII, a non-metal. It is easier for its atom to accept one electron, which it lacks before the completion of the outer level, than to give up seven electrons from the outer level:
3. First, find the least common multiple between the charges of the formed ions, it is equal to 2 (2x1). Then we determine how many calcium atoms need to be taken so that they donate two electrons, that is, one Ca atom and two CI atoms must be taken.
4. Schematically, the formation of an ionic bond between calcium and chlorine atoms can be written: (slide 8)
Ca 2+ + 2CI - → CaCI 2
Tasks for self-control
1. Based on the scheme for the formation of a chemical compound, make up an equation for a chemical reaction: (slide 9)
2. Based on the scheme for the formation of a chemical compound, make up an equation for a chemical reaction: (slide 10)
3. A scheme for the formation of a chemical compound is given: (slide 11)
Choose a pair of chemical elements whose atoms can interact in accordance with this scheme:
a) Na and O;
b) Li and F;
in) K and O;
G) Na and F
Electrons from one atom can completely transfer to another. This redistribution of charges leads to the formation of positively and negatively charged ions (cations and anions). A special type of interaction arises between them - an ionic bond. Let us consider in more detail the method of its formation, the structure and properties of substances.
Electronegativity
Atoms differ in electronegativity (EO) - the ability to attract electrons to themselves from the valence shells of other particles. For quantitative determination, the scale of relative electronegativity proposed by L. Polling (dimensionless value) is used. The ability to attract electrons from fluorine atoms is more pronounced than other elements, its EO is 4. In the Polling scale, oxygen, nitrogen, and chlorine immediately follow fluorine. The EO values of hydrogen and other typical non-metals are equal to or close to 2. Of the metals, most have electronegativity between 0.7 (Fr) and 1.7. There is a dependence of the bond ionicity on the difference between the EO of chemical elements. The larger it is, the higher the probability that an ionic bond will occur. This type of interaction is more common when the difference EO=1.7 and higher. If the value is less, then the compounds are polar covalent.
Ionization energy
Ionization energy (EI) is required for detachment of external electrons weakly bound to the nucleus. The unit of change of this physical quantity is 1 electron volt. There are patterns of change in EI in the rows and columns of the periodic system, depending on the increase in the charge of the nucleus. In periods from left to right, the ionization energy increases and acquires the highest values for non-metals. In groups, it decreases from top to bottom. The main reason is the increase in the radius of the atom and the distance from the nucleus to the outer electrons, which are easily detached. A positively charged particle appears - the corresponding cation. The value of EI can be used to judge whether an ionic bond occurs. The properties also depend on the ionization energy. For example, alkali and alkaline earth metals have low EI values. They have pronounced reducing (metallic) properties. Inert gases are chemically inactive due to their high ionization energy.
electron affinity
In chemical interactions, atoms can attach electrons to form a negative particle - an anion, the process is accompanied by the release of energy. The corresponding physical quantity is electron affinity. The unit of measurement is the same as the ionization energy (1 electron volt). But its exact values are not known for all elements. Halogens have the highest electron affinity. At the outer level of the atoms of the elements - 7 electrons, only one is missing up to an octet. The electron affinity of halogens is high, they have strong oxidizing (non-metallic) properties.
Interactions of atoms in the formation of an ionic bond
Atoms that have an incomplete external level are in an unstable energy state. The desire to achieve a stable electronic configuration is the main reason that leads to the formation of chemical compounds. The process is usually accompanied by the release of energy and can lead to molecules and crystals that differ in structure and properties. Strong metals and non-metals differ significantly from each other in a number of indicators (EO, EI, and electron affinity). For them, this type of interaction is more suitable as an ionic chemical bond, in which the unifying molecular orbital (common electron pair) moves. It is believed that during the formation of ions, metals completely transfer electrons to non-metals. The strength of the resulting bond depends on the work required to destroy the molecules that make up 1 mol of the substance under study. This physical quantity is known as the binding energy. For ionic compounds, its values range from several tens to hundreds of kJ/mol.
Ion formation
An atom that gives up its electrons during chemical interactions turns into a cation (+). The receiving particle is an anion (-). To find out how atoms will behave, whether ions will appear, it is necessary to establish the difference between their EC. The easiest way to carry out such calculations is for a compound of two elements, for example, sodium chloride.
Sodium has only 11 electrons, the configuration of the outer layer is 3s 1 . To complete it, it is easier for an atom to give up 1 electron than to attach 7. The structure of the valence layer of chlorine is described by the formula 3s 2 3p 5. In total, an atom has 17 electrons, 7 are external. One is missing to achieve an octet and a stable structure. The chemical properties support the assumption that the sodium atom donates and chlorine accepts electrons. There are ions: positive (sodium cation) and negative (chlorine anion).
Ionic bond
Losing an electron, sodium acquires a positive charge and a stable shell of an atom of the inert gas neon (1s 2 2s 2 2p 6). Chlorine, as a result of interaction with sodium, receives an additional negative charge, and the ion repeats the structure of the atomic shell of the noble gas argon (1s 2 2s 2 2p 6 3s 2 3p 6). The acquired electric charge is called the charge of the ion. For example, Na + , Ca 2+ , Cl - , F - . Ions can contain atoms of several elements: NH 4 + , SO 4 2- . Inside such complex ions, the particles are linked by a donor-acceptor or covalent mechanism. Electrostatic attraction occurs between oppositely charged particles. Its value in the case of an ionic bond is proportional to the charges, and with increasing distance between atoms, it weakens. Characteristic features of an ionic bond:
- strong metals react with active non-metallic elements;
- electrons move from one atom to another;
- the resulting ions have a stable configuration of outer shells;
- There is an electrostatic attraction between oppositely charged particles.
Crystal lattices of ionic compounds
In chemical reactions, metals of the 1st, 2nd and 3rd groups of the periodic system usually lose electrons. One-, two- and three-charged positive ions are formed. Nonmetals of the 6th and 7th groups usually add electrons (with the exception of reactions with fluorine). There are singly and doubly charged negative ions. The energy costs for these processes, as a rule, are compensated when a substance crystal is created. Ionic compounds are usually in a solid state, forming structures consisting of oppositely charged cations and anions. These particles are attracted and form giant crystal lattices in which positive ions are surrounded by negative particles (and vice versa). The total charge of a substance is zero, because the total number of protons is balanced by the number of electrons of all atoms.
Properties of substances with an ionic bond
Ionic crystalline substances are characterized by high boiling and melting points. Typically, these compounds are heat resistant. The following feature can be found when such substances are dissolved in a polar solvent (water). Crystals are easily destroyed, and ions pass into a solution that has electrical conductivity. Ionic compounds are also destroyed when melted. Free charged particles appear, which means that the melt conducts electric current. Substances with an ionic bond are electrolytes - conductors of the second kind.
Oxides and halides of alkali and alkaline earth metals belong to the group of ionic compounds. Almost all of them are widely used in science, technology, chemical production, metallurgy.
An ionic chemical bond is a bond that forms between atoms of chemical elements (positively or negatively charged ions). So what is an ionic bond, and how does it form?
General characteristics of the ionic chemical bond
Ions are charged particles that atoms become when they donate or accept electrons. They are attracted to each other quite strongly, it is for this reason that substances with this type of bond have high boiling and melting points.
Rice. 1. Ions.
An ionic bond is a chemical bond between dissimilar ions due to their electrostatic attraction. It can be considered the limiting case of a covalent bond, when the difference between the electronegativity of the bound atoms is so great that complete separation of charges occurs.
Rice. 2. Ionic chemical bond.
It is usually believed that the bond acquires an electronic character if EC > 1.7.
The difference in the value of electronegativity is greater, the further the elements are located from each other in the periodic system by period. This connection is characteristic of metals and non-metals, especially those located in the most remote groups, for example, I and VII.
Example: table salt, sodium chloride NaCl:
Rice. 3. Scheme of the ionic chemical bond of sodium chloride.
The ionic bond exists in crystals, it has strength, length, but is not saturated and not directed. Ionic bonding is characteristic only for complex substances, such as salts, alkalis, and some metal oxides. In the gaseous state, such substances exist in the form of ionic molecules.
An ionic chemical bond is formed between typical metals and non-metals. Electrons without fail pass from the metal to the non-metal, forming ions. As a result, an electrostatic attraction is formed, which is called an ionic bond.
In fact, a completely ionic bond does not occur. The so-called ionic bond is partly ionic, partly covalent. However, the bond of complex molecular ions can be considered ionic.
Examples of ionic bond formation
There are several examples of the formation of an ionic bond:
- interaction of calcium and fluorine
Ca 0 (atom) -2e \u003d Ca 2 + (ion)
It is easier for calcium to donate two electrons than to receive the missing ones.
F 0 (atom) + 1e \u003d F- (ion)
- Fluorine, on the contrary, is easier to accept one electron than to give seven electrons.
Let us find the least common multiple between the charges of the formed ions. It is equal to 2. Let's determine the number of fluorine atoms that will accept two electrons from a calcium atom: 2: 1 = 2. 4.
Let's make a formula for an ionic chemical bond:
Ca 0 +2F 0 →Ca 2 +F−2.
- interaction of sodium and oxygen
| Structural chemistry | |
|---|---|
| Chemical bond: | Aromaticity | Covalent bond | Ionic bond| Metal connection | Hydrogen bond | Donor-acceptor bond | Tautomerism |
| Structure display: | Functional group | Structural formula | Chemical formula | ligand |
| Electronic properties: | Electronegativity | Electron affinity | Ionization energy | Dipole | Octet Rule |
| Stereochemistry: | Asymmetric atom | Isomerism | Configuration | Chirality | Conformation |
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See what "Ionic chemical bond" is in other dictionaries:
The bond between atoms in a molecule or mol. connection, arising as a result of either the transfer of an electron from one atom to another, or the socialization of electrons by a pair (or group) of atoms. The forces leading to X. s. are Coulomb, but X. s. describe within... Physical Encyclopedia
CHEMICAL BOND- interaction of atoms, in which electrons belonging to two different atoms (groups) become common (socialized) for both atoms (groups), causing their combination into molecules and crystals. There are two main types of X. s .: ionic ... ... Great Polytechnic Encyclopedia
CHEMICAL BOND The mechanism by which atoms combine to form molecules. There are several types of such a bond, based either on the attraction of opposite charges, or on the formation of stable configurations through the exchange of electrons. ... ... Scientific and technical encyclopedic dictionary
chemical bond- CHEMICAL BOND, the interaction of atoms, causing their connection into molecules and crystals. The forces acting during the formation of a chemical bond are mainly electrical in nature. The formation of a chemical bond is accompanied by a rearrangement ... ... Illustrated Encyclopedic Dictionary
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Mutual attraction of atoms, leading to the formation of molecules and crystals. It is customary to say that in a molecule or in a crystal between neighboring atoms there are ch. The valence of an atom (which is discussed in more detail below) indicates the number of bonds ... Great Soviet Encyclopedia
chemical bond- mutual attraction of atoms, leading to the formation of molecules and crystals. The valence of an atom shows the number of bonds formed by a given atom with neighboring ones. The term "chemical structure" was introduced by Academician A. M. Butlerov in ... ... Encyclopedic Dictionary of Metallurgy
The interaction of atoms, which determines their connection into molecules and crystals. This interaction leads to a decrease in the total energy of the resulting molecule or crystal compared to the energy of non-interacting atoms and is based on ... ... Big encyclopedic polytechnic dictionary
Covalent bond on the example of a methane molecule: a complete external energy level for hydrogen (H) 2 electrons, and for carbon (C) 8 electrons. Covalent bond bond formed by directed valence electron clouds. Neutral ... ... Wikipedia
Chemical bonding is the phenomenon of the interaction of atoms, due to the overlap of electron clouds, binding particles, which is accompanied by a decrease in the total energy of the system. The term "chemical structure" was first introduced by A. M. Butlerov in 1861 ... ... Wikipedia
