Chemical Bonding - Class 10 Notes
Chemical bonding is a fundamental concept in chemistry that explains how atoms combine to form molecules and compounds. In Class 10, students are introduced to different types of chemical bonds and their properties. Let's explore chemical bonding in detail with examples:
1. Introduction to Chemical Bonding:
Atoms are the basic units of matter. They combine to form molecules and compounds through chemical bonding. Chemical bonding involves the transfer or sharing of electrons between atoms to achieve a stable electron configuration.
2. Types of Chemical Bonds:
a) Ionic Bond:
Ionic bonding occurs when atoms transfer electrons to achieve a stable electron configuration. One atom loses electrons to form a positively charged ion (cation), while another atom gains those electrons to form a negatively charged ion (anion).
Example: Sodium chloride (NaCl) - Sodium (Na) loses an electron to become Na+ cation, and chlorine (Cl) gains that electron to become Cl- anion.
b) Covalent Bond:
Covalent bonding occurs when atoms share electrons to achieve a stable electron configuration. It typically involves nonmetals combining to form molecules.
Example: Water (H2O) - Two hydrogen (H) atoms share electrons with one oxygen (O) atom to form a covalent bond.
3. Lewis Dot Structure:
Lewis dot structures are diagrams that represent the valence electrons of atoms in a molecule or ion. Valence electrons are represented as dots around the atomic symbol.
Example: Lewis Dot Structure of Water (H2O)
O
H - H
Each hydrogen atom shares one electron with the oxygen atom, resulting in a covalent bond.
4. Properties of Ionic and Covalent Compounds:
a) Ionic Compounds:
- Ionic compounds are typically formed between metals and nonmetals.
- They have high melting and boiling points due to strong electrostatic forces between ions.
- They conduct electricity when dissolved in water or in a molten state (ionic solutions).
Example: Sodium chloride (NaCl), magnesium oxide (MgO).
b) Covalent Compounds:
- Covalent compounds are typically formed between nonmetals.
- They have low melting and boiling points as the intermolecular forces are weaker.
- They do not conduct electricity, as they do not produce ions in solution.
Example: Water (H2O), carbon dioxide (CO2).
5. Metallic Bond:
Metallic bonding occurs in metals, where valence electrons are delocalized and move freely between metal atoms. This delocalized electron cloud gives metals their unique properties, such as electrical conductivity and malleability.
6. Electronegativity and Polar Covalent Bonds:
Electronegativity is the tendency of an atom to attract electrons in a chemical bond. In polar covalent bonds, electrons are shared unequally between atoms due to differences in electronegativity.
Example: Polar Covalent Bond in Hydrogen Chloride (HCl)
H - Cl
Chlorine (Cl) is more electronegative than hydrogen (H), leading to a polar covalent bond.
7. Intermolecular Forces:
Intermolecular forces are forces of attraction between molecules. Van der Waals forces and hydrogen bonding are examples of intermolecular forces.
a) Van der Waals Forces:
- Van der Waals forces are weak forces of attraction between nonpolar molecules.
- They occur due to temporary shifts in electron density, creating temporary dipoles in molecules.
Example: Noble gases (e.g., helium, neon) experience Van der Waals forces.
b) Hydrogen Bonding:
- Hydrogen bonding is a special type of dipole-dipole interaction.
- It occurs between a hydrogen atom bonded to an electronegative atom (e.g., nitrogen, oxygen, or fluorine) and another electronegative atom in a different molecule.
Example: Water (H2O) exhibits hydrogen bonding between its hydrogen atoms and oxygen atoms of neighboring water molecules.
8. Covalent Compounds and Hybridization:
Covalent compounds involving carbon often undergo hybridization, where the atomic orbitals of carbon combine to form hybrid orbitals.
Example: Ethane (C2H6)
H H
\ /
C
/ \
H H
In ethane, carbon undergoes sp3 hybridization, resulting in four sigma (σ) bonds with hydrogen.
9. Metallic Bond and Alloys:
Alloys are a mixture of two or more elements, where at least one is a metal. Metallic bonding in alloys provides unique properties such as increased strength and resistance to corrosion.
Example: Steel (Iron-Carbon Alloy)
Steel is an alloy of iron and carbon, where carbon acts as a hardening agent, improving the mechanical properties of iron.
Examples of Chemical Bonding:
a) Sodium Chloride (NaCl):
Ionic Bonding - Sodium (Na) donates an electron to chlorine (Cl).
Result: Na+ cation and Cl- anion are formed, and they attract each other to form the ionic compound NaCl (common salt).
b) Methane (CH4):
Covalent Bonding - Carbon (C) shares electrons with four hydrogen (H) atoms.
Result: Four single covalent bonds are formed, creating the stable methane molecule.
c) Oxygen Molecule (O2):
Covalent Bonding - Two oxygen (O) atoms share electrons to form a double covalent bond.
Result: Oxygen molecule (O2) is formed, which is a stable and diatomic gas.
Octet Rule:
The octet rule states that atoms tend to gain, lose, or share electrons to achieve a stable electron configuration with eight valence electrons.
Exceptions to the Octet Rule:
Some molecules may have fewer or more than eight valence electrons due to the availability of d-orbitals in certain elements.
Example: Phosphorus pentachloride (PCl5) has ten valence electrons around the central phosphorus (P) atom.
Understanding chemical bonding is crucial for understanding the behavior of molecules and compounds in various chemical reactions. It forms the foundation of chemistry and helps explain the diversity of matter and its interactions in the natural world.