Molecular Compounds, Allotropes of Carbon, Polymers, and Ionic
Lattices
Molecular Compounds
Molecular compounds are formed when two or more nonmetals share electrons through covalent bonds.
These compounds are typically composed of discrete molecules with fixed numbers of atoms. Examples
include water (H₂O), carbon dioxide (CO₂), and methane (CH₄).
Allotropes of Carbon
Allotropes are different forms of the same element that have distinct physical and chemical properties. Carbon, a
versatile element, exhibits several allotropes:
● Diamond: A hard, crystalline structure where each carbon atom is bonded to four others in a tetrahedral
arrangement.
● Graphite: A layered structure where each carbon atom is bonded to three others in hexagonal rings.
● Fullerene (Buckminsterfullerene): A spherical molecule composed of 60 carbon atoms arranged in a
pattern resembling a soccer ball.
Polymers
Polymers are large molecules made
up of repeating units called monomers. They can be
natural or synthetic. Examples of natural polymers include proteins and carbohydrates.
Synthetic polymers include plastics like polyethylene and nylon.
Ionic Lattices
Ionic lattices are crystalline structures formed by the electrostatic attraction
between oppositely charged ions. Ionic compounds, such as sodium chloride
(NaCl), are composed of ionic lattices.
Key Points for a Grade 9:
● Understand the difference between molecular compounds and ionic compounds.
● Be able to identify allotropes of carbon and their properties.
● Know the structure and properties of polymers.
● Understand the concept of ionic lattices and their formation.
Lattices
Molecular Compounds
Molecular compounds are formed when two or more nonmetals share electrons through covalent bonds.
These compounds are typically composed of discrete molecules with fixed numbers of atoms. Examples
include water (H₂O), carbon dioxide (CO₂), and methane (CH₄).
Allotropes of Carbon
Allotropes are different forms of the same element that have distinct physical and chemical properties. Carbon, a
versatile element, exhibits several allotropes:
● Diamond: A hard, crystalline structure where each carbon atom is bonded to four others in a tetrahedral
arrangement.
● Graphite: A layered structure where each carbon atom is bonded to three others in hexagonal rings.
● Fullerene (Buckminsterfullerene): A spherical molecule composed of 60 carbon atoms arranged in a
pattern resembling a soccer ball.
Polymers
Polymers are large molecules made
up of repeating units called monomers. They can be
natural or synthetic. Examples of natural polymers include proteins and carbohydrates.
Synthetic polymers include plastics like polyethylene and nylon.
Ionic Lattices
Ionic lattices are crystalline structures formed by the electrostatic attraction
between oppositely charged ions. Ionic compounds, such as sodium chloride
(NaCl), are composed of ionic lattices.
Key Points for a Grade 9:
● Understand the difference between molecular compounds and ionic compounds.
● Be able to identify allotropes of carbon and their properties.
● Know the structure and properties of polymers.
● Understand the concept of ionic lattices and their formation.
