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what are the important points in the chapter chemical bonding?
The attractive force which holds together the constituent particles (atoms, ions 
or molecules) in chemical species is known as chemical bond. 

Tendency or urge atoms of various elements to attain stable configuration of 
eight electrons in their valence shell is cause of chemical combination

The principle of attaining a maximum of eight electrons in the valence shell or 
outermost shell of atoms is known as octet rule.

Electronic Theory: Kossel-Lewis approach to chemical Bonding: Atoms achieve 
stable octet when they are linked by chemical bonds. The atoms do so either 
by transfer or sharing of valence electrons. Inner  shell electrons are not 
involved in combination process

The bond formed by mutual sharing of electrons between the combining     
atoms of the same or different elements is called a covalent bond. 

General Properties of Covalent Compounds: 
1. The covalent compounds do not exist as ions but they exist as 
molecules. 
2. The melting and boiling points of covalent compounds are generally low.  
3. Covalent compounds are generally insoluble or less soluble in water and 
other polar solvents. However, these are soluble in non- polar solvents. 
4. Since covalent compounds do not give ions in solution, these are poor 
conductors of electricity in the fused or dissolved state. 
5. Molecular reactions are quite slow because energy is required to break 
covalent bonds. 
6. Since the covalent bond is localized in between the nuclei of atoms, it is 
directional in nature. 

Co-Ordinate Covalent Bond: 
Covalent type bond in which both the electrons in the shared pair come 
from one atom is called a coordinate covalent bond.  
Co- Ordinate Covalent Bond is usually represented by an  arrow (?) 
pointing from donor to the acceptor atom.  
Co- Ordinate Covalent bond is also called as dative bond, donor – acceptor 
bond, semi- polar bond or co-ionic bond. 

The electrostatic force of attraction which holds the oppositely charged ions 
together is known as ionic bond or electrovalent bond.

Ionic compounds will be formed more easily between the elements with 
comparatively low ionization enthalpy and elements with comparatively high 
negative value of electron gain enthalpy. 

Bond length: It is defined as the average distance between the nuclei of the 
nuclei of two bonded atoms in a molecule.

Covalent radius is half of the distance between two  similar atoms joined by 
single covalent bond in same molecule.

Van der Waals radius is one half of the distance between two similar adjacent 
atoms belonging to two nearest neighbouring molecules of the same substance 
in the solid state. It is always larger than covalent radii. 

Bond angle: It is defined as the average angle between orbitals containing 
bonding electron pairs around the central atom in a molecule.

Bond enthalpy: It is defined as amount of energy required to break one mole 
of bonds of a particular type between atoms in gaseous state.

Bond order: The bond order is defined as the number of bonds between two 
atoms in a molecule.

Resonance: When a molecule cannot be represented by a single structure but 
its characteristic properties can be described by two or more than two 
structures, then the actual structure is said to be a resonance hybrid of these 
structure.

Polarity of Bonds: In reality no bond is completely covalent or completely ionic.


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