notes of chapter 4 of chemistry of class 11
Answers
Answer:
Explanation:
Chemical Bond
The force that holds different atoms in a molecule is called chemical bond.
• Octet Rule
Atoms of different elements take part in chemical combination in order to complete their octet or to attain the noble gas configuration.
• Valence Electrons
It is the outermost shell electron which takes part in chemical combination.
• Facts Stated by Kossel in Relation to Chemical Bonding
— In the periodic table, the highly electronegative halogens and the highly electro-positive alkali metals are separated by noble gases.
— Formation of an anion and cation by the halogens and alkali metals are formed by gain of electron and loss of electron respectively.
— Both the negative and positive ions acquire the noble gas configuration.
— The negative and positive ions are stabilized by electrostatic attraction Example,
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• Modes of Chemical Combination
— By the transfer of electrons: The chemical bond which formed by the complete transfer of one or more electrons from one atom to another is termed as electrovalent bond or ionic bond.
— By sharing of electrons: The bond which is formed by the equal sharing of electrons between one or two atoms is called covalent bond. In these bonds electrons are contributed by both.
— Co-ordinate bond: When the electrons are contributed by one atom and shared by both, the bond is formed and it is known as dative bond or co-ordinate bond.
• Ionic or Electrovalent Bond
Ionic or Electrovalent bond is formed by the complete transfer of electrons from one atom to another. Generally, it is formed between metals and non-metals. We can say that it is the electrostatic force of attraction which holds the oppositely charged ions together.
The compounds which is formed by ionic or electrovalent bond is known as electrovalent compounds. For Example, ,
(i) NaCl is an electrovalent compound. Formation of NaCl is given below:
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Na+ ion has the configuration of Ne while Cl– ion represents the configuration of Ar.
(ii) Formation of magnesium oxide from magnesium and oxygen.
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Electrovalency: Electrovalency is the number of electrons lost or gained during the formation of an ionic bond or electrovalent bond.
• Factors Affecting the Formation of Ionic Bond
(i) Ionization enthalpy: As we know that ionization enthalpy of any element is the amount of energy required to remove an electron from outermost shell of an isolated gaseous atom to convert it into cation.
Hence, lesser the ionization enthalpy, easier will be the formation of a cation and have greater chance to form an ionic bond. Due to this reason alkali metals have more tendency to form an ionic bond.
For example, in formation of Na+ ion I.E = 496 kJ/mole
While in case of magnesium, it is 743 kJ/mole. That’s why the formation of positive ion for sodium is easier than that of magnesium.
Therefore, we can conclude that lower the ionization enthalpy, greater the chances of ionic bond formation.
(ii) Electron gain enthalpy (Electron affinities): It is defined as the energy released when an isolated gaseous atom takes up an electron to form anion. Greater the negative electron gain enthalpy, easier will be the formation of anion. Consequently, the probability of formation of ionic bond increases.
For example. Halogens possess high electron affinity. So, the formation of anion is very common in halogens.
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(iii) Lattice energy or enthalpy: It is defined as the amount of energy required to separate 1 mole of ionic compound into separate oppositely charged ions.
Lattice energy of an ionic compound depends upon following factors:
(i) Size of the ions: Smaller the size, greater will be the lattice energy.
(ii) Charge on the ions: Greater the magnitude of charge, greater the interionic attraction and hence higher the lattice energy.
• General Characteristics of ionic Compounds
(i) Physical’State: They generally exist as crystalline solids, known as crystal lattice. Ionic compounds do not exist as single molecules like other gaseous molecules e.g., H2 , N2 , 02 , Cl2 etc.
(ii) Melting and boiling points: Since ionic compounds contain high interionic force between them, they generally have high melting and boiling points.
(iii) Solubility: They are soluble in polar solvents such as water but do not dissolve in organic solvents like benzene, CCl4etc.
(iv) Electrical conductivity: In solid state they are poor conductors of electricity but in molten state or when dissolved in water, they conduct electricity.
(v) Ionic reactions: Ionic compounds produce ions in the solution which gives very fast reaction with oppositely charged ions.
Answer:
Chemical Bond: The appealing pressure which holds numerous constituents (atoms, ions, etc.) collectively in one-of-a-kind chemical species is referred to as. a chemical bond.
There are numerous theories to explain the formation of a chemical bond. They are
- Kossel-Lewis approach.
- Valence-Shell Electron-Pair Repulsion (VSEPR) Theory
- Valence Bond (VB) Theory
- Molecular Orbital Theory.
Kossel-Lewis Approach to Chemical Bonding: All noble gases [except He] have eight electrons in, their valence shells. They are chemically inactive. In the case of all different factors, there are much less than three electrons withinside the valence shells in their atoms, and as a result, they're chemically reactive.
“The atoms of various factors integrate with every different so as to finish their respective octets (i.e8 electrons of their outermost shell) or duplet (i.e., the outermost shell having 2 electrons in case of H, Li, and Be) to achieve solid inert fueloline configuration”.
Facts for chemical bonding (Kossel)
- The incredibly electronegative halogens and incredibly electropositive alkali metals are separated via way of means of noble gases withinside the periodic table.
- The formation of a poor ion and a superb ion is because of the benefit or lack of electrons via way of means of atoms.
- The poor and superb ions as a result shaped achieve the closest noble fuel line configuration. The noble gases (aside from He which has a duplet of electrons) have a specifically solid outer shell configuration of eight (Octet) electrons, ns2np6.
- The poor and superb ions are stabilized via way of means of electrostatic attraction.
- Electrovalent or Ionic Bond: When a bond is shaped via way of means of the entire transfer of electrons from one atom to any other to finish their octets or duplets the bond is termed an ionic or electrovalent bond.
Factors favoring the formation of an ionic bond.
- Atom going to lose electrons need to have low ionization enthalpy so that it could lose electrons readily. Elements of I and II. corporations choose to form, ionic bonds due to the fact they've low values of Ionisation enthalpy.
- Elements that be given electrons need to have a High Negative Value of electron benefit enthalpy with the purpose to maintain the electrons. Halogens have excessive values of E.G. enthalpy.
- Lattice enthalpy needs to be excessive. This, in turn, relies upon.
(a) Charge at the ion: Greater the rate at the ion, the greater the lattice energy.
(b) Size of the ions: Smaller the ion, the greater the lattice energy.
→ Octet Rule: According to the digital principle of chemical bonding as evolved via way of means of Kossel and Lewis, atoms can integrate both via way of means of the switch of valence electron’s from one atom to any other (benefit or loss) or via way of means of sharing valence electrons to have an octet of their valence shells. This is called the Octet rule.
→ Covalent Bond: A covalent bond is formed because of the mutual sharing of electrons among the 2 atoms to finish their valence e. No. of electrons contributed via way of means of every atom is termed as covalency.
Lone Pairs Of Electrons
- A few atoms which might be bonded have a further pair of electrons that aren't worried about bonding. Such electrons are referred to as lone pairs of electrons. Lewis dot shape represents the association of lone pairs and bonded pairs around every atom of a molecule.
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