EntranceCovalent chemical bond examples. Covalent bond: polar and non-polar, properties and examples
Idea about education chemical bond using a pair of electrons belonging to both connecting atoms, was expressed in 1916 by the American physical chemist J. Lewis.
Covalent bonds exist between atoms in both molecules and crystals. It occurs both between identical atoms (for example, in H2, Cl2, O2 molecules, in a diamond crystal) and between different atoms (for example, in H2O and NH3 molecules, in SiC crystals). Almost all bonds in molecules organic compounds are covalent (C-C, C-H, C-N, etc.).
There are two mechanisms for the formation of covalent bonds:
1) exchange;
2) donor-acceptor.
Exchange mechanism of covalent bond formationlies in the fact that each of the connecting atoms provides one unpaired electron for the formation of a common electron pair (bond). The electrons of interacting atoms must have opposite spins.
Let us consider, for example, the formation of a covalent bond in a hydrogen molecule. When hydrogen atoms come closer, their electron clouds penetrate into each other, which is called overlapping of electron clouds (Fig. 3.2), the electron density between the nuclei increases. The nuclei attract each other. As a result, the energy of the system decreases. When atoms come very close together, the repulsion of nuclei increases. Therefore, there is an optimal distance between the nuclei (bond length l), at which the system has minimum energy. In this state, energy is released, called the binding energy E St.
Rice. 3.2. Diagram of electron cloud overlap during the formation of a hydrogen molecule
Schematically, the formation of a hydrogen molecule from atoms can be represented as follows (a dot means an electron, a line means a pair of electrons):
N + N→N: N or N + N→N - N.
IN general view for AB molecules of other substances:
A + B = A: B.
Donor-acceptor mechanism of covalent bond formationlies in the fact that one particle - the donor - represents an electron pair to form a bond, and the second - the acceptor - represents a free orbital:
A: + B = A: B.
donor acceptor
Let's consider the mechanisms of formation of chemical bonds in the ammonia molecule and ammonium ion.
1. Education
The nitrogen atom has two paired and three unpaired electrons at the outer energy level:
The hydrogen atom in the s sublevel has one unpaired electron.
In the ammonia molecule, the unpaired 2p electrons of the nitrogen atom form three electron pairs with the electrons of 3 hydrogen atoms:
In the NH 3 molecule, 3 covalent bonds are formed according to the exchange mechanism.
2. Formation of a complex ion - ammonium ion.
NH 3 + HCl = NH 4 Cl or NH 3 + H + = NH 4 +
The nitrogen atom remains with a lone pair of electrons, i.e. two electrons with antiparallel spins in one atomic orbital. The atomic orbital of the hydrogen ion contains no electrons (vacant orbital). When an ammonia molecule and a hydrogen ion approach each other, an interaction occurs between the lone pair of electrons of the nitrogen atom and the vacant orbital of the hydrogen ion. The lone pair of electrons becomes common to the nitrogen and hydrogen atoms, and a chemical bond occurs according to the donor-acceptor mechanism. The nitrogen atom of the ammonia molecule is the donor, and the hydrogen ion is the acceptor:
It should be noted that in the NH 4 + ion all four bonds are equivalent and indistinguishable; therefore, in the ion the charge is delocalized (dispersed) throughout the complex.
The considered examples show that the ability of an atom to form covalent bonds is determined not only by one-electron, but also by 2-electron clouds or the presence of free orbitals.
According to the donor-acceptor mechanism, bonds are formed in complex compounds: - ; 2+ ; 2- etc.
A covalent bond has the following properties:
- saturation;
- directionality;
- polarity and polarizability.
Chemical elementary particles tend to connect with each other through the formation of special relationships. They are polar and non-polar. Each of them has a specific formation mechanism and conditions of occurrence.
In contact with
What is this
A covalent bond is a formation that occurs for elements with non-metallic properties. The presence of the prefix “ko” indicates the joint participation of atomic electrons of different elements.
The concept of “valence” means the presence of a certain strength. The emergence of such a relationship occurs through the socialization of atomic electrons that do not have a “pair.”
These chemical bonds arise due to the appearance of a “piggy bank” of electrons, which is common to both interacting particles. The appearance of pairs of electrons is due to the overlapping of electron orbitals. These types of interactions occur between electron clouds both elements.
Important! A covalent bond occurs when a pair of orbitals combines.
Substances with described structure are:
- numerous gases;
- alcohols;
- carbohydrates;
- proteins;
- organic acids.
A covalent chemical bond is formed due to the formation of public pairs of electrons in simple substances or complex compounds. It happens polar and non-polar.
How to determine the nature of a chemical bond? To do this you need to look at atomic component of particles, present in the formula.
Chemical bonds of the described type are formed only between elements where non-metallic properties predominate.
If a compound contains atoms of the same or different non-metals, then the relationships that arise between them are “covalent”.
When a metal and a non-metal are present in a compound at the same time, a relationship is said to be formed.
Structure with "poles"
A covalent polar bond connects atoms of nonmetals of different natures to each other. These can be atoms:
- phosphorus and;
- chlorine and;
- ammonia.
There is another definition for these substances. It suggests that this “chain” is formed between non-metals with different electronegativity indices. In both cases, the variety is “emphasized” chemical elements-atoms where this relationship arose.
The formula of a substance with a polar covalent bond is:
- NO and many others.
Presented compounds in normal conditions can have liquid or gaseous states of aggregation. The Lewis formula helps to more accurately understand the mechanism of binding atomic nuclei.
How it appears
The mechanism of formation of a covalent bond for atomic particles with different electronegativity values comes down to the formation of the overall density of electronic nature.
It usually shifts to the element that has the highest electronegativity. It can be determined using a special table.
Due to the displacement of the common pair of “electrons” towards an element with a higher electronegativity value, a negative charge is partially formed on it.
Accordingly, the other element will receive a partial positive charge. Consequently a connection is formed with two differently charged poles.
Often, when forming a polar relationship, an acceptor mechanism or a donor-acceptor mechanism is used. An example of a substance formed by this mechanism is the ammonia molecule. In it, nitrogen is endowed with a free orbital, and hydrogen is endowed with a free electron. The forming shared electron pair occupies a given nitrogen orbital, as a result of which one element becomes a donor and the other an acceptor.
Mechanism described covalent bond formation, as a type of interaction, is not typical for all compounds with polar binding. Examples include substances of organic as well as inorganic origin.
About non-polar structure
A covalent nonpolar bond connects elements with nonmetallic properties that have same electronegativity values. In other words, substances with covalent nonpolar bonds are compounds consisting of varying amounts of identical nonmetals.
Formula of a substance with a covalent nonpolar bond:
Examples of compounds falling into this category are substances of simple structure. In the formation of this type of interaction, like other non-metallic interactions, “outermost” electrons are involved.
In some literature they are called valence. By refers to the number of electrons required to complete the outer shell. An atom can give or receive negatively charged particles.
The described relationship belongs to the category of two-electron or two-center chains. In this case, a pair of electrons takes general position between two orbitals of elements. IN structural formulas The electron pair is written as a horizontal bar or “-”. Each line shows the number of shared electron pairs in the molecule.
To break substances with this type of relationship, it is necessary to expend the maximum amount of energy, therefore these substances are among the strongest on the strength scale.
Attention! This category includes diamond - one of the strongest compounds in nature.
How it appears
According to the donor-acceptor mechanism, nonpolar bonds are practically not connected. A covalent nonpolar bond is a structure formed by sharing pairs of electrons. These pairs belong equally to both atoms. Multiple linking by Lewis formula more accurately gives an idea of the mechanism of connection of atoms in a molecule.
The similarity between covalent polar and nonpolar bonds is the appearance of a common electron density. Only in the second case, the resulting electron “piggy banks” belong equally to both atoms, occupying a central position. As a result, partial positive and negative charges are not formed, which means that the resulting “chains” are non-polar.
Important! Non-polar bonding results in the formation of a shared electron pair, making the last electron level of the atom complete.
Properties of substances with the described structures differ significantly on the properties of substances with metallic or ionic interactions.
What is a polar covalent bond
What are the types of chemical bonds?
In which one of the atoms gave up an electron and became a cation, and the other atom accepted an electron and became an anion.
The characteristic properties of a covalent bond - directionality, saturation, polarity, polarizability - determine the chemical and physical properties connections.
The direction of the connection is determined molecular structure substances and the geometric shape of their molecules. The angles between two bonds are called bond angles.
Saturability is the ability of atoms to form a limited number of covalent bonds. The number of bonds formed by an atom is limited by the number of its external atomic orbitals.
The polarity of the bond is due to the uneven distribution of electron density due to differences in the electronegativity of the atoms. On this basis, covalent bonds are divided into non-polar and polar (non-polar - a diatomic molecule consists of identical atoms (H 2, Cl 2, N 2) and the electron clouds of each atom are distributed symmetrically relative to these atoms; polar - a diatomic molecule consists of atoms of different chemical elements , and the total electron cloud shifts towards one of the atoms, thereby forming an asymmetry of the distribution electric charge in a molecule, generating a dipole moment of the molecule).
Bond polarizability is expressed in the displacement of bond electrons under the influence of external electric field, including another reacting particle. Polarizability is determined by electron mobility. The polarity and polarizability of covalent bonds determines the reactivity of molecules towards polar reagents.
However, two-time Nobel Prize winner L. Pauling pointed out that “in some molecules there are covalent bonds due to one or three electrons instead of a common pair.” A one-electron chemical bond is realized in the molecular hydrogen ion H 2 +.
The molecular hydrogen ion H2+ contains two protons and one electron. The single electron of the molecular system compensates for the electrostatic repulsion of the two protons and holds them at a distance of 1.06 Å (the length of the H 2 + chemical bond). The center of electron density of the electron cloud of the molecular system is equidistant from both protons at the Bohr radius α 0 =0.53 A and is the center of symmetry of the molecular hydrogen ion H 2 + .
Encyclopedic YouTube
-
1 / 5
A covalent bond is formed by a pair of electrons shared between two atoms, and these electrons must occupy two stable orbitals, one from each atom.
A + + B → A: B
As a result of socialization, electrons form a filled energy level. A bond is formed if their total energy at this level is less than in the initial state (and the difference in energy will be nothing more than the bond energy).
According to the theory of molecular orbitals, the overlap of two atomic orbitals leads, in the simplest case, to the formation of two molecular orbitals (MO): linking MO And anti-binding (loosening) MO. The shared electrons are located on the lower energy bonding MO.
Bond formation during recombination of atoms
However, the mechanism of interatomic interaction for a long time remained unknown. Only in 1930 F. London introduced the concept of dispersion attraction - the interaction between instantaneous and induced (induced) dipoles. Currently, the attractive forces caused by the interaction between the fluctuating electric dipoles of atoms and molecules are called “London forces”.
The energy of such an interaction is directly proportional to the square of the electronic polarizability α and inversely proportional to the distance between two atoms or molecules to the sixth power.
Bond formation by donor-acceptor mechanism
In addition to the homogeneous mechanism of covalent bond formation outlined in the previous section, there is a heterogeneous mechanism - the interaction of oppositely charged ions - the H + proton and the negative hydrogen ion H -, called hydride ion:
H + + H - → H 2
As the ions approach, the two-electron cloud (electron pair) of the hydride ion is attracted to the proton and ultimately becomes common to both hydrogen nuclei, that is, it turns into a bonding electron pair. The particle that supplies an electron pair is called a donor, and the particle that accepts this electron pair is called an acceptor. This mechanism of covalent bond formation is called donor-acceptor.
H + + H 2 O → H 3 O +
A proton attacks the lone electron pair of a water molecule and forms a stable cation that exists in aqueous solutions of acids.
Similarly, a proton is added to an ammonia molecule to form a complex ammonium cation:
NH 3 + H + → NH 4 +
In this way (according to the donor-acceptor mechanism of covalent bond formation) a large class of onium compounds is obtained, which includes ammonium, oxonium, phosphonium, sulfonium and other compounds.
A hydrogen molecule can act as a donor of an electron pair, which, upon contact with a proton, leads to the formation of a molecular hydrogen ion H 3 +:
H 2 + H + → H 3 +
The bonding electron pair of the molecular hydrogen ion H 3 + belongs simultaneously to three protons.
Types of covalent bond
There are three types of covalent chemical bonds, differing in the mechanism of formation:
1. Simple covalent bond. For its formation, each atom provides one unpaired electron. When a simple covalent bond is formed, the formal charges of the atoms remain unchanged.
- If the atoms forming a simple covalent bond are the same, then the true charges of the atoms in the molecule are also the same, since the atoms forming the bond equally own a shared electron pair. This connection is called non-polar covalent bond. Simple substances have such a connection, for example: 2, 2, 2. But not only nonmetals of the same type can form a covalent nonpolar bond. Non-metal elements whose electronegativity is of equal importance can also form a covalent nonpolar bond, for example, in the PH 3 molecule the bond is covalent nonpolar, since the EO of hydrogen is equal to the EO of phosphorus.
- If the atoms are different, then the degree of possession of a shared pair of electrons is determined by the difference in the electronegativity of the atoms. An atom with greater electronegativity attracts a pair of bonding electrons more strongly toward itself, and its true charge becomes negative. An atom with lower electronegativity acquires, accordingly, a positive charge of the same magnitude. If a compound is formed between two different non-metals, then such a compound is called covalent polar bond.
In the ethylene molecule C 2 H 4 there is a double bond CH 2 = CH 2, its electronic formula: H:C::C:H. The nuclei of all ethylene atoms are located in the same plane. The three electron clouds of each carbon atom form three covalent bonds with other atoms in the same plane (with angles between them of approximately 120°). The cloud of the fourth valence electron of the carbon atom is located above and below the plane of the molecule. Such electron clouds of both carbon atoms, partially overlapping above and below the plane of the molecule, form a second bond between the carbon atoms. The first, stronger covalent bond between carbon atoms is called a σ bond; the second, weaker covalent bond is called π (\displaystyle \pi )- communication.
In a linear acetylene molecule
N-S≡S-N (N: S::: S: N)
there are σ bonds between carbon and hydrogen atoms, one σ bond between two carbon atoms and two π (\displaystyle \pi )-bonds between the same carbon atoms. Two π (\displaystyle \pi )-bonds are located above the sphere of action of the σ-bond in two mutually perpendicular planes.
All six carbon atoms of the cyclic benzene molecule C 6 H 6 lie in the same plane. There are σ bonds between carbon atoms in the plane of the ring; Each carbon atom has the same bonds with hydrogen atoms. Carbon atoms spend three electrons to make these bonds. Clouds of fourth valence electrons of carbon atoms, shaped like figures of eight, are located perpendicular to the plane of the benzene molecule. Each such cloud overlaps equally with the electron clouds of neighboring carbon atoms. In a benzene molecule, not three separate π (\displaystyle \pi )-connections, but a single π (\displaystyle \pi) dielectrics or semiconductors. Typical examples of atomic crystals (atoms in which are connected to each other by covalent (atomic) bonds) are
Part I
1. Electronegativity (EO) is the ability of atoms to attract electron pairs to themselves.
3. If a covalent chemical bond is formed between atoms of different non-metal elements, then shared electron pairs are biased toward the more electronegative element. An excess negative charge appears on it, and an excess positive charge appears on the partner atom. This connection is called covalent polar.
5. Complete the table “Covalent polar bond”.
Part II
1. Play tic-tac-toe. Show the winning path consisting of the formulas of substances with a polar covalent bond and write down the schemes for their formation.
2. Select the formulas of compounds with a covalent polar chemical bond. From the letters corresponding to the correct answers, you will form a word meaning an imitation of a diamond or other precious stone made of glass: rhinestone.
1) HF C
3) FeBr3 T
5) SO2 P
7) CO2 A
9) PCl5 Z3. Construct a graph of the dependence of the atomic number of a chemical element on the electronegativity of elements of the same period. Find exact electronegativity values using the Internet. Draw a conclusion:
As the serial number increases, the EO increases.4. Construct a graph of the dependence of the atomic number of a chemical element on the electronegativity of elements of one main subgroup. Find the exact values of electronegativity using the Internet.
In a group, as the serial number increases, the EO decreases.5. The most polar chemical bond in a molecule is:
4) hydrogen fluoride - HF6. Arrange the following substances in order of decreasing polarity of chemical bond.
4) potassium phosphide - K3P
2) aluminum phosphide - AlP
3) phosphorus chloride (V) - PCl5
1) white phosphorus - P4Topics of the Unified State Examination codifier: Covalent chemical bond, its varieties and mechanisms of formation. Characteristics of covalent bonds (polarity and bond energy). Ionic bond. Metal connection. Hydrogen bond
Intramolecular chemical bonds
First, let's look at the bonds that arise between particles within molecules. Such connections are called intramolecular.
Chemical bond between atoms of chemical elements has an electrostatic nature and is formed due to interaction of external (valence) electrons, in more or less degree held by positively charged nuclei bonded atoms.
The key concept here is ELECTRONEGATIVITY. It is this that determines the type of chemical bond between atoms and the properties of this bond.
is the ability of an atom to attract (hold) external(valence) electrons. Electronegativity is determined by the degree of attraction of outer electrons to the nucleus and depends primarily on the radius of the atom and the charge of the nucleus.
Electronegativity is difficult to determine unambiguously. L. Pauling compiled a table of relative electronegativities (based on the bond energies of diatomic molecules). The most electronegative element is fluorine with meaning 4 .
It is important to note that in different sources you can find different scales and tables of electronegativity values. This should not be alarmed, since the formation of a chemical bond plays a role atoms, and it is approximately the same in any system.
If one of the atoms in the A:B chemical bond attracts electrons more strongly, then the electron pair moves towards it. The more electronegativity difference atoms, the more the electron pair shifts.
If the electronegativities of interacting atoms are equal or approximately equal: EO(A)≈EO(B), then the common electron pair does not shift to any of the atoms: A: B. This connection is called covalent nonpolar.
If the electronegativities of the interacting atoms differ, but not greatly (the difference in electronegativity is approximately from 0.4 to 2: 0,4<ΔЭО<2 ), then the electron pair is displaced to one of the atoms. This connection is called covalent polar .
If the electronegativities of interacting atoms differ significantly (the difference in electronegativity is greater than 2: ΔEO>2), then one of the electrons is almost completely transferred to another atom, with the formation ions. This connection is called ionic.
Basic types of chemical bonds − covalent, ionic And metal communications. Let's take a closer look at them.
Covalent chemical bond
Covalent bond – it's a chemical bond , formed due to formation of a common electron pair A:B . Moreover, two atoms overlap atomic orbitals. A covalent bond is formed by the interaction of atoms with a small difference in electronegativity (usually between two non-metals) or atoms of one element.
Basic properties of covalent bonds
- focus,
- saturability,
- polarity,
- polarizability.
These bonding properties influence the chemical and physical properties of substances.
Communication direction characterizes the chemical structure and form of substances. The angles between two bonds are called bond angles. For example, in a water molecule the bond angle H-O-H is 104.45 o, therefore the water molecule is polar, and in a methane molecule the bond angle H-C-H is 108 o 28′.
Saturability is the ability of atoms to form a limited number of covalent chemical bonds. The number of bonds that an atom can form is called.
Polarity bonding occurs due to the uneven distribution of electron density between two atoms with different electronegativity. Covalent bonds are divided into polar and nonpolar.
Polarizability connections are the ability of bond electrons to shift under the influence of an external electric field(in particular, the electric field of another particle). Polarizability depends on electron mobility. The further the electron is from the nucleus, the more mobile it is, and accordingly the molecule is more polarizable.
Covalent nonpolar chemical bond
There are 2 types of covalent bonding – POLAR And NON-POLAR .
Example . Let's consider the structure of the hydrogen molecule H2. Each hydrogen atom in its outer energy level carries 1 unpaired electron. To display an atom, we use the Lewis structure - this is a diagram of the structure of the outer energy level of an atom, when electrons are indicated by dots. Lewis point structure models are quite helpful when working with elements of the second period.
H. + . H = H:H
Thus, a hydrogen molecule has one shared electron pair and one H–H chemical bond. This electron pair does not shift to any of the hydrogen atoms, because Hydrogen atoms have the same electronegativity. This connection is called covalent nonpolar .
Covalent nonpolar (symmetric) bond is a covalent bond formed by atoms with equal electronegativity (usually the same nonmetals) and, therefore, with a uniform distribution of electron density between the nuclei of atoms.
The dipole moment of non-polar bonds is 0.
Examples: H 2 (H-H), O 2 (O=O), S 8.
Covalent polar chemical bond
Covalent polar bond is a covalent bond that occurs between atoms with different electronegativity (usually, various non-metals) and is characterized displacement shared electron pair to a more electronegative atom (polarization).
The electron density is shifted to the more electronegative atom - therefore, a partial negative charge (δ-) appears on it, and a partial positive charge (δ+, delta +) appears on the less electronegative atom.
The greater the difference in electronegativity of atoms, the higher polarity connections and more dipole moment . Additional attractive forces act between neighboring molecules and charges of opposite sign, which increases strength communications.
Bond polarity affects the physical and chemical properties of compounds. The reaction mechanisms and even the reactivity of neighboring bonds depend on the polarity of the bond. The polarity of the connection often determines molecule polarity and thus directly affects such physical properties as boiling point and melting point, solubility in polar solvents.
Examples: HCl, CO 2, NH 3.
Mechanisms of covalent bond formation
Covalent chemical bonds can occur by 2 mechanisms:
1. Exchange mechanism the formation of a covalent chemical bond is when each particle provides one unpaired electron to form a common electron pair:
A . + . B= A:B
2. Covalent bond formation is a mechanism in which one of the particles provides a lone pair of electrons, and the other particle provides a vacant orbital for this electron pair:
A: + B= A:B
In this case, one of the atoms provides a lone pair of electrons ( donor), and the other atom provides a vacant orbital for that pair ( acceptor). As a result of the formation of both bonds, the energy of the electrons decreases, i.e. this is beneficial for the atoms.
A covalent bond formed by a donor-acceptor mechanism is not different in properties from other covalent bonds formed by the exchange mechanism. The formation of a covalent bond by the donor-acceptor mechanism is typical for atoms either with a large number of electrons at the external energy level (electron donors), or, conversely, with a very small number of electrons (electron acceptors). The valence capabilities of atoms are discussed in more detail in the corresponding section.
A covalent bond is formed by a donor-acceptor mechanism:
- in a molecule carbon monoxide CO(the bond in the molecule is triple, 2 bonds are formed by the exchange mechanism, one by the donor-acceptor mechanism): C≡O;
- V ammonium ion NH 4 +, in ions organic amines, for example, in the methylammonium ion CH 3 -NH 2 + ;
- V complex compounds, a chemical bond between the central atom and ligand groups, for example, in sodium tetrahydroxoaluminate Na bond between aluminum and hydroxide ions;
- V nitric acid and its salts- nitrates: HNO 3, NaNO 3, in some other nitrogen compounds;
- in a molecule ozone O3.
Basic characteristics of covalent bonds
Covalent bonds typically form between nonmetal atoms. The main characteristics of a covalent bond are length, energy, multiplicity and directionality.
Multiplicity of chemical bond
Multiplicity of chemical bond - This number of shared electron pairs between two atoms in a compound. The multiplicity of a bond can be determined quite easily from the values of the atoms that form the molecule.
For example , in the hydrogen molecule H 2 the bond multiplicity is 1, because Each hydrogen has only 1 unpaired electron in its outer energy level, hence one shared electron pair is formed.
In the O 2 oxygen molecule, the bond multiplicity is 2, because Each atom at the outer energy level has 2 unpaired electrons: O=O.
In the nitrogen molecule N2, the bond multiplicity is 3, because between each atom there are 3 unpaired electrons at the outer energy level, and the atoms form 3 common electron pairs N≡N.
Covalent bond length
Chemical bond length is the distance between the centers of the nuclei of the atoms forming the bond. It is determined by experimental physical methods. The bond length can be estimated approximately using the additivity rule, according to which the bond length in the AB molecule is approximately equal to half the sum of the bond lengths in molecules A 2 and B 2:
The length of a chemical bond can be roughly estimated by atomic radii forming a bond, or by communication multiplicity, if the radii of the atoms are not very different.
As the radii of the atoms forming a bond increase, the bond length will increase.
For example
As the multiplicity of bonds between atoms increases (the atomic radii of which do not differ or differ only slightly), the bond length will decrease.
For example . In the series: C–C, C=C, C≡C, the bond length decreases.
Communication energy
A measure of the strength of a chemical bond is the bond energy. Communication energy determined by the energy required to break a bond and remove the atoms forming that bond to an infinitely large distance from each other.
A covalent bond is very durable. Its energy ranges from several tens to several hundred kJ/mol. The higher the bond energy, the greater the bond strength, and vice versa.
The strength of a chemical bond depends on the bond length, bond polarity, and bond multiplicity. The longer a chemical bond, the easier it is to break, and the lower the bond energy, the lower its strength. The shorter the chemical bond, the stronger it is, and the greater the bond energy.
For example, in the series of compounds HF, HCl, HBr from left to right, the strength of the chemical bond decreases, because The connection length increases.
Ionic chemical bond
Ionic bond is a chemical bond based on electrostatic attraction of ions.
Ions are formed in the process of accepting or donating electrons by atoms. For example, atoms of all metals weakly hold electrons from the outer energy level. Therefore, metal atoms are characterized by restorative properties- ability to donate electrons.
Example. The sodium atom contains 1 electron at energy level 3. By easily giving it up, the sodium atom forms the much more stable Na + ion, with the electron configuration of the noble gas neon Ne. The sodium ion contains 11 protons and only 10 electrons, so the total charge of the ion is -10+11 = +1:
+11Na) 2 ) 8 ) 1 - 1e = +11 Na +) 2 ) 8
Example. A chlorine atom in its outer energy level contains 7 electrons. To acquire the configuration of a stable inert argon atom Ar, chlorine needs to gain 1 electron. After adding an electron, a stable chlorine ion is formed, consisting of electrons. The total charge of the ion is -1:
+17Cl) 2 ) 8 ) 7 + 1e = +17 Cl — ) 2 ) 8 ) 8
Note:
- The properties of ions are different from the properties of atoms!
- Stable ions can form not only atoms, but also groups of atoms. For example: ammonium ion NH 4 +, sulfate ion SO 4 2-, etc. Chemical bonds formed by such ions are also considered ionic;
- Ionic bonds are usually formed between each other metals And nonmetals(non-metal groups);
The resulting ions are attracted due to electrical attraction: Na + Cl -, Na 2 + SO 4 2-.
Let us visually summarize difference between covalent and ionic bond types:
Metal connection is a connection that is formed relatively free electrons between metal ions, forming a crystal lattice.
Metal atoms are usually located on the outer energy level one to three electrons. The radii of metal atoms, as a rule, are large - therefore, metal atoms, unlike non-metals, give up their outer electrons quite easily, i.e. are strong reducing agents.
By donating electrons, metal atoms turn into positively charged ions . The detached electrons are relatively free are moving between positively charged metal ions. Between these particles a connection arises, because shared electrons hold metal cations arranged in layers together , thus creating a fairly strong metal crystal lattice . In this case, the electrons continuously move chaotically, i.e. New neutral atoms and new cations constantly appear.
Intermolecular interactions
Separately, it is worth considering the interactions that arise between individual molecules in a substance - intermolecular interactions . Intermolecular interactions are a type of interaction between neutral atoms in which no new covalent bonds appear. The forces of interaction between molecules were discovered by Van der Waals in 1869, and named after him Van dar Waals forces. Van der Waals forces are divided into orientation, induction And dispersive . The energy of intermolecular interactions is much less than the energy of chemical bonds.
Orientation forces of attraction occur between polar molecules (dipole-dipole interaction). These forces occur between polar molecules. Inductive interactions is the interaction between a polar molecule and a non-polar one. A nonpolar molecule is polarized due to the action of a polar one, which generates additional electrostatic attraction.
A special type of intermolecular interaction is hydrogen bonds. - these are intermolecular (or intramolecular) chemical bonds that arise between molecules that have highly polar covalent bonds - H-F, H-O or H-N. If there are such bonds in a molecule, then between the molecules there will be additional attractive forces .
Education mechanism hydrogen bonding is partly electrostatic and partly donor-acceptor. In this case, the electron pair donor is an atom of a strongly electronegative element (F, O, N), and the acceptor is the hydrogen atoms connected to these atoms. Hydrogen bonds are characterized by focus in space and saturation
Hydrogen bonds can be indicated by dots: H ··· O. The greater the electronegativity of the atom connected to hydrogen, and the smaller its size, the stronger the hydrogen bond. It is typical primarily for connections fluorine with hydrogen , as well as to oxygen and hydrogen , less nitrogen with hydrogen .
Hydrogen bonds occur between the following substances:
— hydrogen fluoride HF(gas, solution of hydrogen fluoride in water - hydrofluoric acid), water H 2 O (steam, ice, liquid water):
— solution of ammonia and organic amines- between ammonia and water molecules;
— organic compounds in which O-H or N-H bonds: alcohols, carboxylic acids, amines, amino acids, phenols, aniline and its derivatives, proteins, solutions of carbohydrates - monosaccharides and disaccharides.
Hydrogen bonding affects the physical and chemical properties of substances. Thus, additional attraction between molecules makes it difficult for substances to boil. Substances with hydrogen bonds exhibit an abnormal increase in boiling point.
For example As a rule, with increasing molecular weight, an increase in the boiling point of substances is observed. However, in a number of substances H 2 O-H 2 S-H 2 Se-H 2 Te we do not observe a linear change in boiling points.
Namely, at water boiling point is abnormally high - no less than -61 o C, as the straight line shows us, but much more, +100 o C. This anomaly is explained by the presence of hydrogen bonds between water molecules. Therefore, under normal conditions (0-20 o C) water is liquid by phase state.