In this post, we will explore the topics of Grade IX Chemistry Chapter 4 "Structure of molecules". The topics, we are going to discuss in this article, are Ionic Bond and Covalent bond formation by giving relevant examples.
If you are a student of Grade IX level Science or preparing for competitive exams, such as EATA, NTS, MDCAT, etc, or even if you are a lecturer or subject teacher of Chemistry this post may be your one-stop solution.
Define the Ionic bond. What conditions must be fulfilled to form an Ionic bond illustrate your answer by giving a suitable example(s)?
Ionic bond
That type of chemical bond which is formed by the transfer of electrons from an electropositive to an electronegative atom is called an Ionic bond. Or
The bond formed between oppositely charged ions due to the electrostatic force of attraction is called an Ionic bond.
History
W.Kossel, a German chemist, in 1916 introduced the concept of the Ionic bond.
For explaining the Ionic bond formation, we take the example of Sodium Chloride (NaCl) and Calcium Chloride (CaCl2).
A. Example of Ionic bond formation in Sodium Chloride
Before discussing the process of formation of Ionic Bond in NaCl, we have to know the electronic configuration of Sodium (Na) and Chlorine (Cl) for better understanding.
|
Electronic configuration of
Na |
Electronic configuration of
Cl |
||
|
Atomic No = 11 No of electron = 11 |
Atomic No = 17 No of electron = 17 |
||
|
In shells |
In sub-shells |
In Shells |
In sub-shells |
|
K=2 |
1s2 |
K=2 |
1s2 |
|
L=8 |
2s2,2p6 |
L=8 |
2s2,2p6 |
|
M=1 |
3s1 |
M=7 |
3s2, 3p5 |
Na will form an Ionic bond with Cl under the following steps.
1. Formation of Cation (positive charge)
Sodium has one valence electron, in order to complete its shell, it will give an electron to Cl. In this way, Na will develop a positive charge on it and will thus become Cation i.e. Na+, thus Na+1 gains the electronic configuration of Neon (Ne).
2. Formation of Anion (negative charge)
Chlorine has seven valence electrons, in order to complete its shell, it will gain one electron from Na. In this way Cl will develop a negative charge on it and will thus become Anion i.e. Cl-, thus Cl-1 gains the electronic configuration of Argon (Ar).
3. Establishment of Electrostatic force of attraction
Na+ and Cl- will then attract each other through electrostatic force of attraction to form an Ionic compound of Sodium Chloride (NaCl).
B. Example of CaCl2 (Calcium Chloride)
Ionic bond can also be formed by the transfer of two electrons as can be seen below example.
1. Formation of Cation (positive charge)
Calcium has two valence electrons, in order to complete its shell, it will give two electrons to two Cl atoms. In this way Ca develop a double positive charge on it and will thus become a cation i.e. Ca+2.
2. Formation of Anion (negative charge)
Chlorine has seven valence electrons, in order to complete its shell, it will accept one electron each from Ca. In this way, Cl will develop a negative charge on it and will thus become Anion i.e. Cl-.
3. Establishment of Electrostatic force of attraction
Ca+2 and two Cl-1 will then attract each other through electrostatic force of attraction to form an Ionic compound of Calcium Chloride (CaCl2).
The force of attraction between two opposite charges that are at rest is called the Electrostatic force of attraction.
Define and explain the formation of the Covalent bond. Also, describe types of Covalent bonds with examples.
Covalent bond
That type of chemical bond in which two or more bonded atoms mutually share their valence electrons is called a Covalent bond.
History
G.N Lewis, an American chemist, 1916 introduced the concept
of the covalent bond.
Explanation
In a Covalent bond, no transfers of electrons take place, but electrons are shared by bonded atoms. For example, in an H2 molecule, two Hydrogen atoms share their valence electron to obey the doublet rule.
Types of Covalent bond
On the basis of the number of shared pairs of electrons, the Covalent bond can be classified into the following three types
1. Single Covalent bond
That type of Covalent bond in which the bonded atoms share two electrons i.e. one pair is called a Single Covalent bond.
A single covalent bond is represented by two dots or a single bar line.
Examples of single covalent bond
a. Formation of Cl2 molecule
A chlorine molecule is formed from two chlorine atoms. The electronic configuration of Cl is (2, 8, 7), so the chlorine atom has seven valence electrons. When two chlorine atoms are brought together, they share 1-1 electron with each other to form a Chlorine molecule (Cl2). In this way, chlorine atoms attain the electronic configuration of inert gas Argon and complete their octet.
b. Formation of Methane (CH4) molecule
As Carbon has four valence electrons and needs four more to attain the noble gas configuration of Neon. Therefore, when combine with four other Hydrogen atoms, form four single covalent bonds.
2. Double Covalent bond
That type of Covalent bond in which the bonded atoms share four electrons i.e. two pairs is called a Double Covalent bond.
A double Covalent bond is represented by four dots or more precisely by a double bar line.
Example of double covalent bond
a. Formation of Oxygen molecule (O2)
The electronic configuration of Oxygen is (2, 6). As Oxygen
has six valence electrons so it shares two electrons with another Oxygen atom
to attain the noble gas configuration of Neon and complete its octet.
b. Formation of CO2
In the Carbon-di-Oxide molecule, Carbon shares four electrons with an Oxygen atom and forms two double covalent bonds.
3. Triple Covalent bond
That type of Covalent bond in which the bonded atoms share six electrons i.e. three pairs is called a triple Covalent bond.
A triple Covalent bond is represented by six dots or more precisely by triple bar lines.
Examples of Triple covalent bonds
a. Formation of Nitrogen molecule (N2)
Nitrogen has five valence electrons (2, 5). It shares three electrons with another Nitrogen atom to form Nitrogen molecule. In this way it attain the noble gas electronic configuration of Neon and complete its octet.
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