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CHEMICAL BONDS


CHEMICAL BONDS


Introduction


A chemical bond is the force of attraction that holds atoms or ions together to form molecules or compounds. Atoms combine with each other to attain maximum stability by achieving a noble gas configuration (octet rule or duplet rule). Chemical bonding explains the formation, structure, and properties of substances and is fundamental to chemistry and life sciences.


Octet Rule

Atoms tend to gain, lose, or share electrons to acquire eight electrons in their valence shell. Exceptions:
Hydrogen and helium (duplet)
Expanded octet (P, S, Cl)
Incomplete octet (B, Al)


Causes of Chemical Bond Formation


Attainment of stable electronic configuration
Decrease in potential energy
Completion of valence shell
Electrostatic attraction between atoms

Types of Chemical Bonds

Chemical bonds are mainly classified into:
Ionic bond
Covalent bond
Coordinate (dative) bond
Metallic bond
Hydrogen bond
van der Waals forces


1. Ionic Bond (Electrovalent Bond)

Definition


An ionic bond is formed by the complete transfer of one or more electrons from one atom to another, resulting in oppositely charged ions held together by electrostatic forces.

Formation

Occurs mainly between metals and non-metals with a large electronegativity difference.
Example: NaCl
Na → Na⁺ + e⁻
Cl + e⁻ → Cl⁻
Na⁺ and Cl⁻ attract each other.

Properties

High melting and boiling points
Soluble in water
Conduct electricity in molten and aqueous states
Hard and brittle crystalline solids
Examples
NaCl, KBr, MgO, CaCl₂

2. Covalent Bond

Definition
A covalent bond is formed by mutual sharing of electrons between atoms.
Types of Covalent Bonds
Single bond: One pair of electrons (H–H)
Double bond: Two pairs (O=O)
Triple bond: Three pairs (N≡N)
Polar and Non-polar Covalent Bonds
Non-polar: Equal sharing (H₂, O₂)
Polar: Unequal sharing due to electronegativity difference (HCl, H₂O)

Properties

Low melting and boiling points
Poor electrical conductivity
Exist as gases, liquids, or soft solids.

Examples

H₂O, CO₂, CH₄, NH₃

3. Coordinate (Dative) Bond

Definition
A coordinate bond is a type of covalent bond in which both electrons are donated by the same atom.
Conditions
Donor atom with a lone pair
Acceptor atom with a vacant orbital
Examples
NH₄⁺ (Ammonium ion)
H₃O⁺ (Hydronium ion)
Characteristics
Represented by an arrow (→)
Once formed, behaves like a normal covalent bond.

4. Metallic Bond

Definition
A metallic bond is the force of attraction between positively charged metal ions and a sea of delocalized valence electrons.
Electron Sea Model
Valence electrons are free to move throughout the metal lattice.
Properties
High electrical and thermal conductivity
Malleability and ductility
Metallic luster
Examples
Fe, Cu, Na, Al

5. Hydrogen Bond


Definition
A hydrogen bond is a weak electrostatic attraction between a hydrogen atom covalently bonded to a highly electronegative atom (O, N, F) and another electronegative atom.

Types

Intermolecular: Between molecules (H₂O)
Intramolecular: Within the same molecule
Importance
High boiling point of water
Stability of proteins and nucleic acids
Essential for DNA double helix structure

6. van der Waals Forces


Weak intermolecular forces including:
Dipole–dipole interactions
London dispersion forces
Important in non-polar molecules and molecular crystals.
Bond Parameters
Bond Length
Distance between nuclei of bonded atoms
Shorter bond → stronger bond
Bond Energy
Energy required to break a bond
Higher bond energy → greater stability
Bond Angle
Angle between bonds in a molecule
Determines molecular geometry


Factors Affecting Bond Formation


Electronegativity difference
Atomic size
Ionization energy
Electron affinity
Valency


Importance of Chemical Bonds


Formation of molecules and compounds
Determines physical and chemical properties
Basis of biochemical molecules like proteins, DNA
Essential for chemical reactions and life processes.

Conclusion


Chemical bonding explains how atoms combine to form stable substances. The nature of chemical bonds—ionic, covalent, coordinate, metallic, hydrogen, and van der Waals—determines the structure, properties, and behavior of matter. A thorough understanding of chemical bonds is fundamental to chemistry, biology, and material science.


MCQ   



1. Chemical bond is
A. A magnetic force
B. A force holding atoms together
C. A repulsive force
D. A nuclear force
Answer: B

2. Chemical bonding results in
A. Higher energy state
B. Unstable atoms
C. Lower potential energy
D. Radioactivity
Answer: C

3. Atoms combine mainly to attain
A. High mass
B. Noble gas configuration
C. Large size
D. High pressure
Answer: B


4. Which rule explains stability of atoms?
A. Hund’s rule
B. Pauli exclusion principle
C. Octet rule
D. Aufbau principle
Answer: C

5. Ionic bond is formed by
A. Sharing of electrons
B. Transfer of electrons
C. Sharing of protons
D. Transfer of neutrons
Answer: B


6. Ionic bonding occurs between
A. Two metals
B. Two non-metals
C. Metal and non-metal
D. Noble gases
Answer: C

7. Example of ionic compound is
A. H₂O
B. CO₂
C. NaCl
D. NH₃
Answer: C

8. Covalent bond is formed by
A. Transfer of electrons
B. Sharing of electrons
C. Loss of electrons
D. Gain of electrons
Answer: B

9. A single covalent bond contains
A. One electron
B. One pair of electrons
C. Two pairs of electrons
D. Three pairs of electrons
Answer: B


10. A triple bond consists of
A. One pair of electrons
B. Two pairs of electrons
C. Three pairs of electrons
D. Four pairs of electrons
Answer: C
11. Which molecule has a triple bond?
A. O₂
B. N₂
C. H₂
D. Cl₂
Answer: B
12. Polar covalent bond is due to
A. Equal sharing of electrons
B. Unequal sharing of electrons
C. Complete electron transfer
D. Absence of electrons
Answer: B
13. Non-polar covalent bond occurs when
A. Electronegativity difference is large
B. Electronegativity difference is zero
C. Ionic character is high
D. Atom is metal
Answer: B
14. Which compound shows polar covalent bonding?
A. H₂
B. O₂
C. HCl
D. N₂
Answer: C
15. Coordinate bond involves
A. Equal sharing of electrons
B. One atom donating both electrons
C. Transfer of electrons
D. Free electrons
Answer: B
16. Which ion contains coordinate bond?
A. Na⁺
B. Cl⁻
C. NH₄⁺
D. Mg²⁺
Answer: C
17. Coordinate bond is represented by
A. –
B. =
C. ≡
D. →
Answer: D
18. Metallic bond is found in
A. Non-metals
B. Ionic compounds
C. Metals
D. Noble gases
Answer: C
19. Metallic bonding is explained by
A. Octet rule
B. VSEPR theory
C. Electron sea model
D. Hybridization
Answer: C
20. Malleability of metals is due to
A. Ionic bond
B. Covalent bond
C. Metallic bond
D. Hydrogen bond
Answer: C
21. Hydrogen bond is a
A. Strong covalent bond
B. Weak intermolecular force
C. Ionic bond
D. Metallic bond
Answer: B
22. Hydrogen bonding occurs when hydrogen is attached to
A. Carbon
B. Sulphur
C. Oxygen, nitrogen or fluorine
D. Chlorine
Answer: C
23. Hydrogen bonding is responsible for
A. Low boiling point of water
B. High boiling point of water
C. Insolubility of water
D. Color of water
Answer: B
24. DNA double helix is stabilized by
A. Ionic bonds
B. Covalent bonds
C. Hydrogen bonds
D. Metallic bonds
Answer: C
25. van der Waals forces are
A. Strong bonds
B. Weak intermolecular forces
C. Ionic forces
D. Nuclear forces
Answer: B
26. Bond energy is
A. Energy released on breaking a bond
B. Energy required to break a bond
C. Distance between atoms
D. Angle between bonds
Answer: B
27. Stronger bonds have
A. Longer bond length
B. Lower bond energy
C. Higher bond energy
D. No bond energy
Answer: C
28. Bond length is the distance between
A. Electron clouds
B. Atomic radii
C. Nuclei of bonded atoms
D. Orbitals
Answer: C
29. Bond length decreases when
A. Bond strength decreases
B. Bond strength increases
C. Atomic size increases
D. Temperature increases
Answer: B
30. Which bond allows electrical conductivity in molten state?
A. Covalent
B. Ionic
C. Hydrogen
D. van der Waals
Answer: B
31. Ionic compounds are usually
A. Soft and malleable
B. Volatile
C. Hard and brittle
D. Gaseous
Answer: C
32. Covalent compounds generally have
A. High melting point
B. Low melting point
C. High conductivity
D. Metallic luster
Answer: B
33. Which element violates octet rule?
A. Carbon
B. Oxygen
C. Boron
D. Nitrogen
Answer: C
34. Expanded octet is seen in
A. Hydrogen
B. Carbon
C. Sulphur
D. Helium
Answer: C
35. Which compound has hydrogen bonding?
A. CH₄
B. NH₃
C. CO₂
D. CCl₄
Answer: B
36. Which bond is strongest?
A. Hydrogen bond
B. van der Waals force
C. Covalent bond
D. Dipole interaction
Answer: C
37. Which property is NOT shown by covalent compounds?
A. Directional bonding
B. Electrical conductivity
C. Low melting point
D. Molecular nature
Answer: B
38. Which compound is non-polar?
A. HCl
B. NH₃
C. H₂O
D. O₂
Answer: D
39. Bond angle helps in determining
A. Atomic number
B. Molecular shape
C. Mass number
D. Electronegativity
Answer: B
40. The strongest intermolecular force is
A. van der Waals force
B. Dipole–dipole interaction
C. Hydrogen bond
D. London force
Answer: C
41. Ionic character increases with
A. Decreasing electronegativity difference
B. Increasing electronegativity difference
C. Decreasing atomic size
D. Increasing covalent nature
Answer: B
42. Which molecule has only covalent bonds?
A. NaCl
B. KBr
C. CO₂
D. MgO
Answer: C
43. Which bond is directionless?
A. Covalent
B. Ionic
C. Coordinate
D. Hydrogen
Answer: B
44. Sea of electrons is associated with
A. Covalent bonding
B. Ionic bonding
C. Metallic bonding
D. Hydrogen bonding
Answer: C
45. Which factor does NOT affect bond formation?
A. Electronegativity
B. Ionization energy
C. Valency
D. Color
Answer: D
46. Which compound conducts electricity in aqueous solution?
A. Sugar
B. Ethanol
C. NaCl
D. Benzene
Answer: C
47. Hydrogen bond is stronger than
A. Covalent bond
B. Ionic bond
C. van der Waals force
D. Metallic bond
Answer: C
48. Which bond is present in NH₃ molecule?
A. Ionic
B. Covalent
C. Metallic
D. Hydrogen only
Answer: B
49. Chemical bonds determine
A. Nuclear stability
B. Physical and chemical properties
C. Atomic mass
D. Isotopes
Answer: B
50. The study of chemical bonding is essential to understand
A. Nuclear reactions
B. Atomic structure only
C. Molecular structure and reactions
D. Radioactivity
Answer: C




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