NCERT Solutions Chemistry Notes for Class 11-Chemical Bonding
Chemistry notes for class 11 CBSE exams preparation at Takshila Learning!
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The discussion is as follows-
A Chemical bond is an attraction between atoms or we can say elements (are the simplest type of matter containing only one kind of atom). A chemical bond enables the formation of a chemical compound. Hence a compound can be defined as a substance consisting of two or more different or same kind of elements that are bonded chemically. The chemical bonds hold the elements together and form temporary connections that are essential for life. The atoms can be connected together by strong bonds or by weak bonds.
The chemical bonds are essential to the chemistry of a living organism as well as to the stability of the environment in which it lives.
The elements combine in two general ways, and both involve the electrons (outermost or valence electrons) of the atoms of the interacting elements:
- Ionic Bond/ Ionic Compounds: They are formed by the transfer of electrons from one element to another element.
- Covalent Bond/ Covalent Compounds: They are formed by sharing of electrons between the atoms of different elements.
Ionic Bonds: An ionic bond is formed when the atoms are held together by electrostatic forces. These compounds are called ionic compound or electrovalent compounds.The compound is neutral overall, as it consists of positively charged ions called cations and negatively charged ions called anions. These can be simple ions such as the sodium (Na+) and chloride (Cl–) in sodium chloride, or polyatomic species such as the ammonium (NH4+) and carbonate (CO3-2) ions in ammonium carbonate. Individual ions within an ionic compound usually have multiple nearest neighbors, so are not considered to be part of molecules, but instead part of a continuous three-dimensional network, usually in a crystalline structure.
Note: Ionic compounds are made up of a metal and a non- metal (except ammonium chloride which is made up of only non-metals.
Covalent Bonds: A covalent bond is also known as molecular bond. It is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs, and there is a stable balance of attractive and repulsive forces between atoms when they share electrons.In the molecule H2 ( the simplest covalent molecule is the diatomic hydrogen molecule), the hydrogen atoms share the two electrons via covalent bonding. Covalency is greatest between atoms of similar electronegativities. Thus, covalent bonding does not necessarily require that the two atoms be of the same elements, only that they should be of comparable electronegativity. The covalent bonding that entails sharing of electrons over more than two atoms is said to be delocalized.
Distinguishing covalent compounds and ionic compounds
- Most covalent compounds consist of molecules. For example: – A cup of water consists of individual water molecules, lying near each other.
In contrast, there are no molecules in an ionic compound. For example: – A piece of sodium chloride is a continuous array in three dimensions of oppositely charged sodium and chloride ions, not an individual collection of sodium and chloride molecules.
- Covalent bonding involves the mutual attraction between two (positively charged) nuclei and the two (negatively charged) electrons that reside between them.
Ionic bonding involves the mutual attraction between positive and negative ions.