Chapter 4.
Chemical bond is the attractive force which holds various consequent together in a molecule. The tendency of atom of various element to attend stable configuration of eight electrons in their valence shell is the cause of chemical combination.
Kossel Lewis approach to chemical bonding.
All the electrons in an atom are not involved in the process of combination. The inner shell electron are well protected and therefore they will participate. 10 the electrons in the outermost shell take part in the chemical combination. these are also called valence shell electron.
Lewis introduced a simple notation to represent valence electron in an atom. These are called Lewis symbols for electron dot symbol.
According to language notation the symbol of element represents the whole of the atom except the valence electrons. The valence electrons are represented by placing dot or process around the symbol.
Significance of Lewis symbols:-
The Lewis symbols indicate the number of electron in the outermost or valence shell which help to calculate common for group valence.
The group valence of the element is generally either equal to total number of dots in Lewis symbols or 8 minus the number of dots or valence electrons.
For example: lithium has one electron in valence shell and it can involve this electron in chemical combination process. Thus it is monovalent.
Octet rules and modes of chemical combination:
According to this atoms achieve the stable octet when they are linked by chemical bond.
*Ionic bond: Thus atoms combine either by transfer of valence electrons from one atom to another.
*covalent bond: By sharing of valence electrons in order to have octet in their valence shells.
Ionic or electrovalent bond:
Electrostatic force of attraction which holds the oppositely charged Ion together is known as ionic bond or electrovalent bond.
For example: ionic bonding in sodium chloride,
Sodium (2,8,1) has one electron more than a stable noble gas structure (2,8) . If it gave away that electron it would become more stable. Hance sodium lose electron and it attains +ve charge on sodium.
Chlorine (2,8,8) has 1 electron dot of stable noble gas structure. It c o u l d gain an electron from somewhere it would become more stable. Chlorine electron and attend negative charge.
Na 2,8,1 Na^+ 2,8
Cl 2,8,7 Cl 2,8,8
FACTORS INFLUENCING IONIC BOND FORMATION:-
We have learnt that in the ionic bond formation, one atom loses one or more electrons while the other accept them. The cation and anion forms as a result Army actually attracted by electrostatic force of attraction. The formation of ionic bond according to kossel's postulation depends upon the following factors:
1. Ionization enthalpy. In the formation of positive Ion or cation, one of the atom is lose electron and from this ionization enthalpy is needed. As already started, it is is the amount of energy required to remove the most loosely Bond electron from an isolated gaseous atom.thus, lesser the ionization enthalpy required, easier will be the formation of cation. For example,
The alkali metal and alkaline earth metal present in the S-block normally form cation since they have comparatively low ionization enthalpies.
2. Electron gain enthalpy.
The electrons release in the formation of Italian are to be accepted by the other atom taking part in the ionic bond formation. The electron accepting tendency of an atom depend upon the electron gain enthalpy. It may be defined as the energy released when an isolated gaseous atom take up an electron to form anion. Greater the negative electron gain enthalpy, is there will be formation of anion. For example,
The halogens present in the group 17 have the maximum tendency to form an iron as they have very high negative electron gain enthalpy.
The member of the oxygen family (group 16) such as oxygen also form anions but not so easily because energy is needed to form divalent anion is comparatively high.
3. Lattice energy or enthalpy.
The ionic compound exist as crystalline solid and the arrangement is known as crystal letters. The ions are changed spieces, energy known as lattice energy or enthalpy is release in the extraction of the iron. It may be defined as: the energy released when 1 mole of crystalline solid is formed by the combination of A positively charged ions.
It is donated as U.
Thus, greater the magnitude of lattice energy, more will be the stability of the ionic bond or ionic compound. The lattice energy depends upon the following factors:
(a). size of the ions.
The size of the Ion influences the lattice energy. Smaller the size, lesser will be the internuclear distance and, thus, greater will be the lattice energy full scope for example, lattice energy of NaCl is more then that of KCL because the radius of Na+ (95pm) ion is smaller as compared to K+ (133pm) ion.
(b). Charge on the ions.
Greater the magnitude of charge on the iron, higher will be the inter ionic attraction and thus, greater will be the value of lattice energy.
General characteristics of ionic compounds:
The common properties of ionic compound are briefly discussed.
1. Physical state.
Ionic compounds are generally exist and crystalline solid in which oppositely charged ions are closely packed in space. The arrangement is known as crystal and letters the nature of the latest depend upon the size and charge on the iron. It may be donated the ionic compound do not exist as single molecule like other gaseous molecule like H2, N2, O2 etc. These exist as network of iron. The crystal lattice of sodium chloride is shown in figure.
2. Melting and boiling points. Because of the presence of a strong inter ionic for the ionic compound have generally high melting and boiling points.
3. Electrical conductivity.
The electrical conductivity of the ionic compound is because of the movement of Ions. They are poor conductor in the solid state in the ionic mobility is almost mil. However, these compounds become conducting either in molten state or when dissolved in water or any other polar solvent since ions can move freely.
4. Solubility.
Ionic or electrovalent compound generally dissolved in a solvent live waterful topic school in daska solvents, the polar molecules interact with the Iron of the crystalline solid. Generally energy is released as result of eight. If water is the solvent, then the energy released is known as hydration energy or enthalpy. The energy released overcomes the inter ionic force and iron thus, get separated and go into the solution. The ionic compound do not dissolve in organic solvent like benzene carbon tetrachloride etc. Because these are non polar in nature.
5. Ionic reactions. The ionic compound react with each other through iron which are formed in solution the moment these are dissolved in water. There for take path in ionic reaction which are very fast and do not require any specific condition full stop for example, when aqueous solution of NaCl and AgNO3 are mixed, a white precipitate of AgCl is immediately formed.
Chemical properties and molecular structures.
Chemical Bond:-Chemical bond is the attractive force which holds various consequent together in a molecule. The tendency of atom of various element to attend stable configuration of eight electrons in their valence shell is the cause of chemical combination.
Kossel Lewis approach to chemical bonding.
All the electrons in an atom are not involved in the process of combination. The inner shell electron are well protected and therefore they will participate. 10 the electrons in the outermost shell take part in the chemical combination. these are also called valence shell electron.
Lewis introduced a simple notation to represent valence electron in an atom. These are called Lewis symbols for electron dot symbol.
According to language notation the symbol of element represents the whole of the atom except the valence electrons. The valence electrons are represented by placing dot or process around the symbol.
The Lewis symbols indicate the number of electron in the outermost or valence shell which help to calculate common for group valence.
The group valence of the element is generally either equal to total number of dots in Lewis symbols or 8 minus the number of dots or valence electrons.
For example: lithium has one electron in valence shell and it can involve this electron in chemical combination process. Thus it is monovalent.
Octet rules and modes of chemical combination:
According to this atoms achieve the stable octet when they are linked by chemical bond.
*Ionic bond: Thus atoms combine either by transfer of valence electrons from one atom to another.
*covalent bond: By sharing of valence electrons in order to have octet in their valence shells.
Ionic or electrovalent bond:
Electrostatic force of attraction which holds the oppositely charged Ion together is known as ionic bond or electrovalent bond.
For example: ionic bonding in sodium chloride,
Sodium (2,8,1) has one electron more than a stable noble gas structure (2,8) . If it gave away that electron it would become more stable. Hance sodium lose electron and it attains +ve charge on sodium.
Chlorine (2,8,8) has 1 electron dot of stable noble gas structure. It c o u l d gain an electron from somewhere it would become more stable. Chlorine electron and attend negative charge.
Na 2,8,1 Na^+ 2,8
Cl 2,8,7 Cl 2,8,8FACTORS INFLUENCING IONIC BOND FORMATION:-
We have learnt that in the ionic bond formation, one atom loses one or more electrons while the other accept them. The cation and anion forms as a result Army actually attracted by electrostatic force of attraction. The formation of ionic bond according to kossel's postulation depends upon the following factors:
1. Ionization enthalpy. In the formation of positive Ion or cation, one of the atom is lose electron and from this ionization enthalpy is needed. As already started, it is is the amount of energy required to remove the most loosely Bond electron from an isolated gaseous atom.thus, lesser the ionization enthalpy required, easier will be the formation of cation. For example,
2. Electron gain enthalpy.
The electrons release in the formation of Italian are to be accepted by the other atom taking part in the ionic bond formation. The electron accepting tendency of an atom depend upon the electron gain enthalpy. It may be defined as the energy released when an isolated gaseous atom take up an electron to form anion. Greater the negative electron gain enthalpy, is there will be formation of anion. For example,
The member of the oxygen family (group 16) such as oxygen also form anions but not so easily because energy is needed to form divalent anion is comparatively high.
3. Lattice energy or enthalpy.
The ionic compound exist as crystalline solid and the arrangement is known as crystal letters. The ions are changed spieces, energy known as lattice energy or enthalpy is release in the extraction of the iron. It may be defined as: the energy released when 1 mole of crystalline solid is formed by the combination of A positively charged ions.
It is donated as U.
Thus, greater the magnitude of lattice energy, more will be the stability of the ionic bond or ionic compound. The lattice energy depends upon the following factors:
(a). size of the ions.
The size of the Ion influences the lattice energy. Smaller the size, lesser will be the internuclear distance and, thus, greater will be the lattice energy full scope for example, lattice energy of NaCl is more then that of KCL because the radius of Na+ (95pm) ion is smaller as compared to K+ (133pm) ion.
(b). Charge on the ions.
Greater the magnitude of charge on the iron, higher will be the inter ionic attraction and thus, greater will be the value of lattice energy.
General characteristics of ionic compounds:
The common properties of ionic compound are briefly discussed.
1. Physical state.
Ionic compounds are generally exist and crystalline solid in which oppositely charged ions are closely packed in space. The arrangement is known as crystal and letters the nature of the latest depend upon the size and charge on the iron. It may be donated the ionic compound do not exist as single molecule like other gaseous molecule like H2, N2, O2 etc. These exist as network of iron. The crystal lattice of sodium chloride is shown in figure.
3. Electrical conductivity.
The electrical conductivity of the ionic compound is because of the movement of Ions. They are poor conductor in the solid state in the ionic mobility is almost mil. However, these compounds become conducting either in molten state or when dissolved in water or any other polar solvent since ions can move freely.
4. Solubility.
Ionic or electrovalent compound generally dissolved in a solvent live waterful topic school in daska solvents, the polar molecules interact with the Iron of the crystalline solid. Generally energy is released as result of eight. If water is the solvent, then the energy released is known as hydration energy or enthalpy. The energy released overcomes the inter ionic force and iron thus, get separated and go into the solution. The ionic compound do not dissolve in organic solvent like benzene carbon tetrachloride etc. Because these are non polar in nature.
5. Ionic reactions. The ionic compound react with each other through iron which are formed in solution the moment these are dissolved in water. There for take path in ionic reaction which are very fast and do not require any specific condition full stop for example, when aqueous solution of NaCl and AgNO3 are mixed, a white precipitate of AgCl is immediately formed.
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