Early ideas about atoms

• What do atoms consist of?

  An atom consists of a nucleus containing protons and neutrons, surrounded by electrons in shells.
• How can the numbers of subatomic particles in an atom be calculated?

  The numbers of subatomic particles can be calculated from its atomic number and mass number.
• What are the early ideas about atoms and their evolution?

  • Ideas about atoms have changed over time.
  • Scientists developed new atomic models as they gathered new experimental evidence.
  • John Dalton published his ideas in 1803, proposing that all matter is made of tiny indivisible particles called atoms.
• Who published ideas about atoms in 1803?

  John Dalton
• What did John Dalton imagine atoms to be like?

  He imagined atoms as tiny spheres that could not be divided.
• What significant discovery did J J Thomson make nearly 100 years after Dalton?

  He discovered the electron.
• What model of the atom did J J Thomson propose?

  He proposed the plum pudding model of the atom.
• How is the plum pudding model described?

  It describes the atom as a ball of positive charge with negative electrons embedded in it.
• What experiment did Ernest Rutherford design in 1909, and what was its purpose?

  • Rutherford designed an experiment to test the plum pudding model.
  • He fired positively charged alpha particles at thin gold foil.
  • The purpose was to observe how the alpha particles interacted with the foil.
• What were the results of Rutherford's experiment with alpha particles and gold foil?

  Most alpha particles went straight through the foil, but a few were scattered in different directions.
• What conclusion did Rutherford draw from his experiment?

  He suggested a new model for the atom called the nuclear model.
• What are the key features of the nuclear model of the atom?

  • The mass of an atom is concentrated at its center, the nucleus.
  • The nucleus contains protons and neutrons.
  • The nucleus is positively charged.
• What is the central part of an atom called?

  The central part of an atom is called the nucleus.
• What particles are contained in the nucleus of an atom?

  The nucleus contains protons and neutrons.
• What is the charge of the nucleus of an atom?

  The nucleus is positively charged.