Particle Nature of Matter: Atoms MCQs Quiz | Class 9

This Class IX Science (Code 086) quiz covers Unit I: Matter – Its Nature and Behaviour, specifically focusing on the Particle Nature of Matter: Atoms. Topics include the concept of the atom, the atom as a basic unit, historical perspectives by Maharishi Kanad and Democritus, Dalton’s Atomic Theory, and chemical symbols. Test your understanding, check your score, and download the solution PDF.

Understanding Atoms: The Building Blocks of Matter

Atoms are the fundamental building blocks of all matter. The idea that matter is composed of tiny, indivisible particles has roots in ancient philosophy. Indian philosopher Maharishi Kanad postulated that if we keep dividing matter, we will reach a particle that cannot be divided further, which he called Parmanu. Similarly, Greek philosopher Democritus called these indivisible particles atoms.

Dalton’s Atomic Theory

In 1808, John Dalton presented his atomic theory, which provided a scientific basis for the nature of matter. Key postulates include:

  • All matter is made of very tiny particles called atoms.
  • Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction.
  • Atoms of a given element are identical in mass and chemical properties.
  • Atoms of different elements have different masses and chemical properties.
  • Atoms combine in the ratio of small whole numbers to form compounds.

Size of an Atom

Atoms are incredibly small, much smaller than anything we can imagine. Atomic radius is measured in nanometres (nm).

  • 1 nanometre = 10^-9 metres (1/10^9 m).
  • For example, the radius of a hydrogen atom is approximately 10^-10 m.

Modern Day Symbols of Atoms

IUPAC (International Union of Pure and Applied Chemistry) approves names of elements. Many symbols are the first one or two letters of the element’s name in English. The first letter is always uppercase, and the second is lowercase.

Element Symbol Element Symbol
Hydrogen H Aluminum Al
Carbon C Cobalt Co
Oxygen O Chlorine Cl
Iron Fe (Ferrum) Sodium Na (Natrium)
Potassium K (Kalium) Gold Au (Aurum)

Extra Practice Questions

  • Q1: Why are atoms not visible to the naked eye?
    Ans: Because they are extremely small, in the order of nanometres (10^-9 m).
  • Q2: What is the atomic mass unit?
    Ans: It is a mass unit equal to exactly one-twelfth (1/12th) the mass of one atom of carbon-12.
  • Q3: Write the symbol for Lead.
    Ans: Pb (from Plumbum).
  • Q4: Which postulate of Dalton’s theory is the result of the Law of Conservation of Mass?
    Ans: “Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction.”
  • Q5: How do atoms exist?
    Ans: Atoms of most elements are not able to exist independently; they form molecules or ions.