Chemistry is called the science of matter and change, but at a deeper level, chemistry is really about how atoms and their interaction. Why does sodium react violently with water? Why is diamond extremely hard while graphite is soft? Why does water have a high boiling point compared to methane? The answer to all these questions lies in chemical bonding.
Chemical Bonding and Molecular Structure, which is taught in Class 10 and 12 Chemistry, as well is part of JEE and NEET syllabus is a high-weightage and important chapter. Questions are usually direct, conceptual, and closely based on NCERT theory. If your fundamentals of bonding are strong, many chapters like coordination compounds, thermodynamics, and organic chemistry become easier.
Let us understand bond theory and different types of chemical bonds step by step.
Why Do Atoms Form Bonds?
Atoms are generally unstable when they exist alone. Most atoms try to achieve a stable electronic configuration, usually that of the nearest noble gas.
Octet Rule
Atoms tend to combine in such a way that they have:
- 8 electrons in their valence shell (for most elements)
- 2 electrons for hydrogen and helium
This drive toward stability leads to the formation of chemical bonds.
Example:
- Sodium (Na): 2,8,1
- Chlorine (Cl): 2,8,7
Sodium can lose one electron and chlorine can gain one electron. Both achieve noble gas configuration → bond formation occurs.
What Is a Chemical Bond?
A chemical bond is the attractive force that holds atoms or ions together in a molecule or compound.
Following are the main type of bonds:
- Ionic bond
- Covalent bond
- Coordinate (dative) bond
- Metallic bond
- Hydrogen bond (intermolecular force, but very important)
Ionic Bond (Electrovalent Bond)
Definition
An ionic bond is formed by complete transfer of one or more electrons from one atom to another, resulting in the formation of oppositely charged ions which attract each other.
Conditions for Ionic Bond Formation
- One atom should have low ionization energy (usually metals)
- Other atom should have high electron affinity (usually non-metals)
- High lattice energy of the compound
Example: Formation of NaCl
- Na → Na⁺ + e⁻
- Cl + e⁻ → Cl⁻
The electrostatic attraction between Na⁺ and Cl⁻ forms NaCl.
Properties of Ionic Compounds
- High melting and boiling points
- Soluble in water
- Conduct electricity in molten or aqueous state
- Hard and brittle
Important Tips on Ionic bond
Ionic character increases with:
- Higher electronegativity difference
- Larger cation and smaller anion
Covalent Bond
Definition
A covalent bond is formed by mutual sharing of electrons between atoms so that each atom achieves a stable configuration.
Example: Formation of H₂ Molecule
Each hydrogen atom has one electron.
- Two hydrogen atoms share one pair of electrons
- Both achieve duplet configuration
This forms a single covalent bond.
Types of Covalent Bonds (Based on Number of Shared Electrons)
| Bond Type | Shared Pairs | Example |
|---|---|---|
| Single bond | 1 | H–H, C–H |
| Double bond | 2 | O=O, C=O |
| Triple bond | 3 | N≡N |
Bond Strength Order : Triple bond> Double bond> Single bond
Bond Length Order: Single > Double > Triple
Polar and Non-Polar Covalent Bonds
Non-Polar Covalent Bond
When electrons are shared equally between atoms with similar electronegativity.
Example:
H₂, O₂, N₂
Polar Covalent Bond
When electrons are shared unequally, resulting in partial charges.
Example:
HCl
- H gets δ⁺
- Cl gets δ⁻
This creates a dipole moment.
Important Formula
Dipole Moment (μ) = charge × distance
Coordinate (Dative) Bond
Definition
A coordinate bond is a covalent bond in which both electrons are donated by the same atom.
Example: Formation of NH₄⁺ (Ammonium Ion)
- NH₃ has one lone pair on nitrogen
- H⁺ has no electrons
- Nitrogen donates its lone pair to H⁺
Bond formed: N → H
Once formed, a coordinate bond behaves like a normal covalent bond.
Other Examples
- H₃O⁺
- CO
- BF₃ + NH₃
Valence Bond Theory (VBT)
According to Valence Bond Theory, when two unfilled atoms interacts, a bond is form over overlap of atomic orbitals where electrons are shared. There more is overlap,mean more are electrons shared, stronger is bond formed
Types of Overlap
(a) Sigma (σ) Bond
- Head-on overlap
- Stronger
- All single bonds are sigma bonds
Examples:
- s–s overlap (H₂)
- s–p overlap (HCl)
- p–p overlap (Cl₂)
(b) Pi (π) Bond
- Sidewise overlap
- Weaker than sigma bond
- Found in double and triple bonds
Bond Composition
- Single bond → 1 σ
- Double bond → 1 σ + 1 π
- Triple bond → 1 σ + 2 π
Hybridization (Very Important topic for JEE and NEET exam)
Hybridization is the mixing of atomic orbitals to form new equivalent hybrid orbitals.
Common Types of Hybridization
| Hybridization | Geometry | Example |
|---|---|---|
| sp | Linear | BeCl₂ |
| sp² | Trigonal planar | BF₃ |
| sp³ | Tetrahedral | CH₄ |
| sp³d | Trigonal bipyramidal | PCl₅ |
| sp³d² | Octahedral | SF₆ |
Shortcut Formula
Hybridization = ½ (σ bonds + lone pairs)
Metallic Bond
In metals, positive ions are surrounded by a sea of delocalized electrons.
Features
- Explains conductivity
- Explains malleability and ductility
- Stronger in metals with more valence electrons
Example
Sodium metal, copper, iron
Hydrogen Bond
Definition
A hydrogen bond is an attractive force between hydrogen attached to a highly electronegative atom (F, O, N) and another electronegative atom.
Types of Hydrogen bonds
- Intermolecular – between molecules (water)
- Intramolecular – within same molecule (o-nitrophenol)
Importance
- High boiling point of water
- Structure of DNA
- Solubility of alcohols
Intermolecular Forces
- Van der Waals forces
- Dipole–dipole interactions
- London dispersion forces
These are weaker than covalent bonds but affect boiling points and physical properties.
Practice Questions on hybridization and bond theory
Conceptual Questions
- Why does NaCl have a higher melting point than MgCl₂?
- Arrange the following in increasing ionic character:
H–Cl, H–F, H–Br, H–I - How many sigma and pi bonds are present in C₂H₂?
- Predict the hybridization of nitrogen in NH₃.
- Why is CO a polar molecule despite having a triple bond?
Numerical / Objective Questions
-
The bond order of O₂⁺ is:
(a) 2
(b) 2.5
(c) 1.5
(d) 1 -
Which molecule has zero dipole moment?
(a) NH₃
(b) H₂O
(c) CO₂
(d) SO₂ -
Number of hydrogen bonds in ice is maximum because:
(a) sp³ hybridization
(b) tetrahedral structure
(c) high electronegativity of oxygen
(d) all of the above
End Note
Chemical bonding is not just a chapter—it is the foundation of chemistry. For JEE and NEET exam, questions are usually NCERT-based, logical, and direct. Focus on:
- Definitions
- Examples
- Trends
- Geometry and hybridization
If you understand why a bond forms, memorization becomes minimal and confidence increases. Keep revising NCERT diagrams and solved examples, and chemical bonding will become one of your strongest scoring chapters.
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