CLASS 9 Chapter 4 Structure of the Atom

Introduction

  • The matter is composed of atoms and molecules.
  • Earlier it was believed that the atom is indivisible.
  • By the end of the nineteenth century, scientists revealed the presence of charged particles in an atom.
  • Atoms are composed of 3 subatomic particles- electron, neutron and neutron.
  • Electrons have a negative charge; protons have a positive charge and neutrons are neutral.
  • The central hard part of an atom is the nucleus which contains protons and neutrons.
  • Electrons are found moving around this nucleus in fixed circular orbits called shells or energy levels.

 

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