Class 9

9.1.4 Allotropic Forms of Elements

This is the fourth lecture from Chapter 1: ‘States of Matter and Phase Changes’ of the new book for 9th Class Chemistry (Punjab Board – PCTB). It discusses the phenomenon of allotropy as well as allotropic forms of elements such as oxygen, carbon and sulphur. The lecture includes a multiple-choice quiz, short-answer questions, and detailed long-answer notes.

MCQs Based Quiz

9.1.4 Allotropic Forms of Elements

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1. Which of the following statements is NOT TRUE for allotropic forms of sulphur (S)?

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2. Which of the following statements is TRUE for fullerenes?

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3. Which allotropic form of carbon has no boundaries, no charge and no unpaired electrons?

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4. Fullerenes are soluble in organic solvents due to:

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5. Which of the following allotropic forms of carbon has layered structure of hexagonal rings of carbon atoms?

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6. There are ____ main allotropic forms of carbon.

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7. Which of the following statements is TRUE for allotropes:

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8. Which of the following statements about fullerenes is TRUE?

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9. What is the structure of Buckminster fullerene (C₆₀)?

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10. Which of the following is NOT an allotrope of carbon?

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11. The property of elements to exist in different structural forms is called:

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Short Questions

Q1. How would you define allotropes?

Allotropes are different structural forms of the same element. They have different physical and chemical properties.
Examples: Graphite, diamond and fullerene are the allotropes of carbon element.

Q2. What is meant by allotropy?

Allotropy is the phenomenon in which an element exists in more than one structural form, each with different physical and chemical properties.
Example: Graphite, diamond and fullerene are the allotropes of carbon element.

Q3. What are the allotropic forms of oxygen element?

Oxygen element exists in two allotropic forms: common oxygen (O2) and ozone (O3).

Q4. Name some allotropic forms of carbon element.

Carbon exists in three common allotropic forms: graphite, diamond and fullerene.

Q5. What is the difference between graphite and diamond?

Graphite has a layered structure of hexagonal rings of carbon atoms, whereas diamond is a giant macromolecule.

Q6. How would you define Buckminster fullerenes?

Buckminster fullerenes (C60) consist of sphere made of carbon atoms arranged in pentagons and hexagons forming a cage like structure.

Q7. Write any two properties of fullerenes.

(Choose any two of the following)
1. Fullerenes are stable at high temperature and pressure.
2. They are covalent in nature.
3. They are soluble in organic solvents.
4. They have no charge, no boundaries and no unpaired electrons.
5. They have low melting point.
6. They are soft and cannot conduct electricity.

Q8. What are the two allotropic forms of sulphur? Which one is more stable?

Sulphur exists in two allotropic forms: rhombic sulphur and monoclinic sulphur. Rhombic sulphur is more stable than monoclinic sulphur.

Descriptive Question

Q1. Write a detailed note on allotropy.

Elements exist in different structural forms called allotropes. These allotropic forms have different physical and chemical properties.

The phenomenon in which an element exists in different structural forms is called allotropy.

Allotropic Forms of Oxygen:

Oxygen element exists in two common allotropic forms, oxygen (O2) and ozone (O3).

Allotropic Forms of Carbon:

Carbon element has three main allotropic forms, diamond, graphite and Buckminster Fullerene.

Diamond:

Diamonds are an allotropic form of carbon that has a giant macromolecular structure.

Graphite:

Graphite is a carbon’s allotropic form which has a layered structure of hexagonal rings of carbon atoms.

Buckminster Fullerene:

Buckminster fullerene is a unique allotropic form of carbon that is made of carbon atoms which are arranged in a hexagons and pentagons.

Properties of Buckminster Fullerenes:

  1. Fullerenes have a cage like structure.
  2. They are stable at high temperature and pressure.
  3. But they have low melting point.
  4. They are soft and cannot conduct electricity.
  5. Their molecules are not charged, has no boundaries and no unpaired electrons.
  6. They are soluble in organic solvents.

Allotropic Forms of Sulphur:

Sulphur exists in two common allotropic forms: Rhombic sulphur (more stable) and monoclinic sulphur (less stable).