CHEMICAL BONDING

Created by
Arun Aby David
Physical Science 2020-22
Peet Memorial Training College ,Mavelikkara

Lewis symbols

In the formation of a chemical bond, only the outermost electrons participate and these electrons are called valence electrons. The inner electrons are well protected and they are called core electrons.  

Here the nucleus and the inner electrons are represented by the symbol of the element and the valence electrons by dots or crosses. 

E.g. for sodium [11Na -2,8,1], the Lewis symbol is Na and for chlorine [17Cl -2,8,7], the Lewis symbol is Cl Lewis symbols are informative. It gives the valency of an atom, which is either equal to the number of dots or crosses or equal to 8 – no. of dots or crosses

Octet Rule

According to this rule, atoms undergo chemical reaction in order to attain octet of electrons in the valence shell. Or, atoms containing 8 electrons in their valence shell are stable. To attain octet, they share electrons or exchange electrons. 

Chemical bonds are the connections between atoms in a molecule. These bonds include both strong intramolecular interactions, such as covalent and ionic bonds. They are related to weaker intermolecular forces, such as dipole-dipole interactions, the London dispersion forces, and hydrogen bonding.

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Chemical Bond

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The attractive force that binds the atoms together in a molecule is called a chemical bond. It is formed either by the transfer of electrons or by the sharing of electrons. 

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Types of Bonds

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1. COVALENT BOND

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A bond formed by the mutual sharing of electrons between two or more atoms is called covalent bond. 

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Example

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Bonds are formed when valence electrons, the electrons in the outermost electronic “shell” of an atom, interact. The nature of the interaction between the atoms depends on their relative *electronegativity. Atoms with equal or similar electronegativity form covalent bonds, in which the valence electron density is shared between the two atoms. The electron density resides between the atoms and is attracted to both nuclei. This type of bond forms most frequently between two non- metals.

When there is a greater electronegativity difference than between covalently bonded atoms, the pair of atoms usually forms a polar covalent bond. The electrons are still shared between the atoms, but the electrons are not equally attracted to both elements. As a result, the electrons tend to be found near one particular atom most of the time. Again, polar covalent bonds tend to occur between non-metals.

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* Electronegativity is the tendency for an atom of a given chemical element to attract shared electrons when forming a chemical bond.

Covalent bonds can be single, double, and triple bonds.

Single bonds occur when two electrons are shared and are composed of one sigma bond between the two atoms.

Double bonds occur when four electrons are shared between the two atoms and consist of one sigma bond and one pi bond.

Triple bonds occur when six electrons are shared between the two atoms and consist of one sigma bond and two pi bonds

For extra reference on Pi bond and sigma bond click herehttps://youtu.be/_qzdRPv4Ns4

2. Ionic Bond

A bond formed by the transfer of electron between 2 atoms is called ionic or electrovalent bond. Or, it is the force of attraction between two oppositely charged ions. 

Example:

Once the oppositely charged ions form, they are attracted by their positive and negative charges and form an ionic compound. Ionic bonds are also formed when there is a large electronegativity difference between two atoms. This difference causes an unequal sharing of electrons such that one atom completely loses one or more electrons and the other atom gains one or more electrons, such as in the creation of an ionic bond between a metal atom (sodium) and a nonmetal (fluorine).

References

SCERT Text book for STD IX
NCERT Text book for STD XI
https://courses.lumenlearning.com/