notes of chapter 4 chemical bonding and molecular structure
Answers
Answer:
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.
Answer:
Hybridisation:
-The atomic orbitals combine to form new set of equivalent orbitals known as hybrid orbitals.
-The hybrid orbitals are used in bond formation.The phenomena is known as hybridisation.
Important conditions for hybridisation:
1.)The orbitals present in the valence shell of the atom are hybridised.
2.)
The orbitals under going hybridisation should have almost equal energy.
3.)Promotion of electron is not essential condition prior to hybridisation.
4.)It is not necessary that only half filled orbitals participate in hybridisation.In some cases, even filled orbitals of valence shell take part in hybridisation.
•Types of hybridisation:
1.)sp Hybridisation:
This type of Hybridisation involves the mixing of one "s" and "p" orbital resulting in the formation of two equivalent sp hybrid orbitals.Which is also known as diagonal hybridisation.
Example: BeCl2.
2.)sp2 Hybridisation:
-In this hybridisation there is involvement to form 3.)equivalent sp2 hybridised orbitals.
- In the excited state,one of the 2s electrons is promoted to vacant 2p orbital asa result boron has three unpaired electrons.
3.)sp3hybridisation:
-The four sp3 hybrid orbitals so formed are directed towards the four corners of the tetrahedron.The angle between sp3 hybrid orbital is 109.5°.
Example: NH3.
•Hybridisation of elements involving d orbitals.
1.)dsp2 - square planar.
2.)sp3d-Trigonal bipyramidal.
3.)sp3d2-Square pyramidal.
4.)sp3d2-Octahedral.