Chemical bonding is the attractive force that holds atoms, ions, or molecules together to form stable chemical substances. The primary purpose of chemical bonding is to enable atoms to attain greater stability by achieving a more favorable electronic configuration, often resembling that of noble gases. Atoms combine because most of them are unstable in their isolated state and tend to lower their energy by losing, gaining, or sharing electrons. Through this process, they form ionic, covalent, or coordinate bonds, resulting in the formation of a vast variety of compounds. Understanding what a chemical bond is, why atoms combine, and how they combine is an important concept in Class 11 Chemistry and forms the foundation for JEE Main, JEE Advanced, NEET, IMUCET, and other competitive examinations.
Class 11 Chemistry Notes for Chapter 4 Chemical Bonding and Molecular Structure With Detail Theory and Explanation
Master Chemical Bonding and Molecular Structure with comprehensive notes, explanations, solved examples, and practice questions designed for Class 11 Chemistry students. Whether you are preparing for school examinations or competitive exams like JEE Main, JEE Advanced, NEET, and IMUCET, this study material will help you build strong fundamentals and improve your confidence in chemistry.
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What is a Chemical Bond ?
Atoms are usually not capable of free existence but groups of atoms of the same or different elements exist as one species e.g. H2, O2, P4, S8, H2O. A group of atoms existing together as one species and having characteristic properties is called molecule. Obviously, there must be some force which holds these atoms together within the molecules. This force vhich holds the aloms together within a molecule is called a chemical bond.
Define Chemical Bond
The attractive force which holds together the constituent particles (atoms, ions or molecules) in a chemical species is known as chemical bond.
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Why Do Atoms Combine? Kossel and Lewis Approach
A number of attempts were made to explain the formation of chemical bonds between atoms in terms of electrons. In 1916, Kossel and Lewis independently succeeded in giving the first successful explanation about the cause of combination between atoms, based upon the understanding of the electronic configuration of noble gases.
(i) Tendency to acquire noble gas configuration or octet rule.
It has been observed that atoms of noble gases have little or no tendency to combine with each other or with atoms of other elements. This means that these atoms must be having stable electronic configurations. The electronic configurations of these elements are given in Table 1.
Table 1. Electronic configurations of noble gases.
| Noble Gas | Atomic Number | Electronic Configuration | Configuration of Valence Shell |
|---|---|---|---|
| Helium (He) | 2 | 1s² | 1s² |
| Neon (Ne) | 10 | 1s² 2s² 2p⁶ | 2s² 2p⁶ |
| Argon (Ar) | 18 | 1s² 2s² 2p⁶ 3s² 3p⁶ | 3s² 3p⁶ |
| Krypton (Kr) | 36 | 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ | 4s² 4p⁶ |
| Xenon (Xe) | 54 | 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ | 5s² 5p⁶ |
| Radon (Rn) | 86 | 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ | 6s² 6p⁶ |
From Table 1, we find that the atoms of all noble gases (with the exception of helium) have eight electrons in their valence shell. Helium on the other hand, has two electrons in its valence shell (first energy shell) because the first energy shell (n = 1) cannot have more than two electrons.
The electronic configuration of the valence shell for all noble gas atoms except helium can be expressed as ns2 np6 (for helium [He], 1s2) and this represents the stable configuration and corresponds to maximum stability. Due to the stable configuration, the noble gas atoms neither have any tendency to gain nor lose electrons and, therefore, their combining capacity (or valency) is zero.
All atoms other than noble gases have less than eight electrons in their outermost shells. In other words, the outermost shells of these atoms do not have stable configurations. Therefore, they combine with each other or with other atoms to achieve stable noble gas electronic configurations (nns2 np6 or 1s2). To a large extent, the elements undergo electronic re-arrangements to attain stable noble gas configurations.
Thus, the tendency or urge of atoms of various elements to attain stable configuration of eight electrons in their valence shells, is the cause of chemical combination.
The principle of attaining maximum of eight electrons in the valence shell of atoms, is called octet rule. However, it may be noted that for hydrogen and lithium atoms, the stable configuration means two electrons which corresponds to the nearest noble gas helium.
(ii) Tendency to acquire minimum energy and stability.
According to modern view, the atoms combine to form chemical bonds to acquire a state of minimum energy. As we know, every system in the universe has a natural tendency to attain a state of minimum energy.
The state of minimum energy corresponds to state of maximum stability. Hence, the atoms combine with each other, only if the process leads to lowering of energy. If there is no fall in potential energy of the system, no bonding is possible.
Exam Tip
The atoms of different elements combine with each other in order to complete their respective octets (i.e. 8 electrons in their outermost shell) or duplet (i.e., outermosl shell having 2 electrons) in case of H, Li and Be to attain stable nearest noble gas configuration.
Explore more concepts related to NCERT Exemplar Solutions Classification of Elements and Periodicity in Properties Class 11 Chemistry
How Do Atoms Combine? Modes of Chemical Combinations
As discussed above, atoms combine together in order to complete their respective octets so as to acquire the stable inert gas configuration. This can occur in two ways :
1. By complete transference of one or more electrons from one atom to another. This process is referred to as electro-valency and the chemical bond formed is termed as electrovalent bond or ionic bond.
2. By sharing of electrons. This can occur in two ways as follows :
(a) When the shared electrons are contributed by the two combining atoms equally the bond formed is called covalent bond.
(b) When these electrons are contributed entirely by one of atoms but shared by both, the bond formed is called co-ordinate bond, also called dative bond.
Related topics include NCERT Solutions: Classification of Elements and Periodicity in Properties Class 11 Chemistry
Short Answer Conceptual Types Questions (SAT)
What is a chemical bond?
A chemical bond is the attractive force that holds together atoms, ions, or molecules in a chemical species. It is formed when atoms combine in order to achieve stable electronic configurations similar to noble gases. The tendency of atoms to attain stability by either losing, gaining, or sharing electrons leads to the formation of chemical bonds.
Why do atoms combine?
Atoms combine mainly for two reasons :
1. To achieve a stable noble gas configuration (Octet Rule). Atoms other than noble gases have incomplete outer shells, so they combine by gaining, losing, or sharing electrons to attain eight electrons in their valence shell (two in the case of hydrogen and lithium). Example : Sodium (Na) loses one electron to achieve the configuration of neon (1s2 2s2 2p6).
2. To achieve minimum energy and maximum stability. Every system in nature tends to attain a state of lower energy, and bond formation helps atoms achieve this stable state.
What is the Octet Rule ?
The Octet Rule states that atoms tend to combine in such a way that each atom achieves eight electrons in its outermost shell, similar to the electronic configuration of noble gases. For Example : Sodium (Na) loses one electron to form Na+, achieving the configuration of neon. Chlorine (Cl) gains one electron to form Cl–, achieving the configuration of argon.
Why are noble gases generally chemically inert?
Noble gases are chemically inert because they already have stable electronic configurations. Their General electronic configuration is ns2 np6 (for helium [He], 1s2). Because of their completely filled valence shells, they neither need to gain, lose, nor share electrons. As a result, their combining capacity (valency) is almost zero.
How does energy change during bond formation?
When a chemical bond is formed, the potential energy of the system decreases. Attractive forces (nucleus–electron) dominate over repulsive forces (nucleus–nucleus, electron–electron). This results in a release of energy, making the system more stable. The greater the energy released during bond formation, the stronger the bond. Thus, bond formation is always an energy-releasing (exothermic) process.
Important Classification of Elements and Periodicity in Properties Chapter Interlinks
This section provides a complete and interconnected study of Classification of Elements and Periodicity in Properties, starting with detailed theory and notes for Class 11 Chemistry to build a strong conceptual foundation. You can explore atomic radius and its types including covalent, van der Waals, metallic, and ionic radii to understand periodic trends in atomic size. It also includes Screening Effect (Shielding Effect) : Calculation of Effective or Reduced Nuclear Charge (Slater’s Rules), which explains how inner electrons reduce the nuclear attraction on outer electrons and influence periodic trends. In addition, topics like Radius of Cation is Less and Anion is More Than Its Parent Atom, Size Variation in Isoelectronic Series help explain how ionic size changes due to gain or loss of electrons and how nuclear charge affects size in species with the same number of electrons. The causes of periodicity explain why elements show repeating properties based on electronic configuration, which is further supported by the modern periodic law and structure of the modern periodic table including groups, periods, and blocks for elements even beyond atomic number 100. The historical development is covered through Mendeleev’s periodic law and table, leading to the modern classification of elements into s, p, d, and f blocks with prediction of period, group, and block. To strengthen exam preparation, you can practice JEE Main PYQs, IMU CET PYQs and Merchant Navy sponsorship exam MCQs, and other previous year questions with solutions, along with solved examples, conceptual questions, and practice problems on the modern periodic table. Learn more in this section also to radius of cation is less and anion is more than its parent atom and size variation in Isoelectronic Series. Additionally, complete study material, mock tests, and guidance are provided under Anand Classes Chemistry notes, along with expert support from Er Neeraj Anand, making this section a comprehensive resource for competitive exam preparation.