Nuclear Model

• • In the nuclear model, most of the atom is empty space. In the centre we have a tiny positive nucleus containing most of the mass of the atom. Around the edge of the atom, we have negative electrons

  
• • Niels Bohr proposed that electrons orbit the nucleus at specific distances called energy levels or shells - this was based on calculations that he had carried out. His proposal was accepted as it agreed with the results of experiments by other scientists
  • Later, scientists found that the positive charge in the nucleus is due to tiny positive particles called protons - number of protons determines the amount of positive charge in the nucleus
  • Around 20 years after the nuclear model was first proposed, James Chadwick discovered the nucleus also contains neutral particles called neutrons

  
• • The radius of an atom is approximately 0.1 nanometers - also written as 1 x 10^ -10 meters
  • The radius of the nucleus is approximately 1 x 10^ -14 meters - less than 1/10000 of the radius of the atom. however nearly all of the mass of the atom is found in the nucleus

  
• • Relative charge is the charge of one particle compared to another particle
  • Protons have a relative charge of positive one
  • Neutrons have a relative charge of zero
  • Electrons have a relative charge of negative one
  • Relative mass means the mass of one particle compared to another particle
  • Protons have a relative mass of one
  • Neutrons have a relative mass of one
  • Electrons have a relative mass of almost zero (1/2000)
  • Atoms have no overall charge as the number of electrons is the same as number of protons