Developing the Model of the Atom

• Who replaced the Plum Pudding Model of the atom?

  Rutherford
• What did John Dalton agree with Democritus about in 1804?

  That matter is made up of tiny spheres
• What was Dalton's contribution to atomic theory?

  He proposed different types of atoms for elements
• What did J.J. Thomson discover nearly 100 years later?

  Electrons
• How did Thomson's findings challenge Dalton's theory?

  Atoms contain smaller particles called electrons
• What did Thomson suggest about the structure of atoms?

  Atoms have positive and negative charges
• What experiment did Rutherford conduct in 1909?

  Firing alpha particles at gold foil
• What was the outcome of Rutherford's gold foil experiment?

  Most particles passed through, some deflected
• What did Rutherford conclude about the atom's structure?

  Atoms have a dense, positively charged nucleus
• What did scientists realize about the mass of the atom?

  Most mass is concentrated in the nucleus
• Why must the nucleus have a positive charge?

  To repel the negatively charged electrons
• What did scientists conclude about the space in an atom?

  Most of the atom is empty space
• What was the first nuclear model of the atom?

  The Rutherford model
• What are the key developments in atomic theory from Dalton to Rutherford?

  • Dalton proposed matter is made of atoms.
  • Thomson discovered electrons and proposed the Plum Pudding Model.
  • Rutherford conducted the gold foil experiment, discovering the nucleus.
• How did the understanding of atomic structure evolve from Dalton to Rutherford?

  From indivisible atoms to a nucleus with electrons
• What did Rutherford's findings imply about atomic mass distribution?

  Mass is concentrated in the nucleus
• What did scientists realize about the particles passing through gold foil?

  Most passed through without deflection
• What did the deflection of some particles in Rutherford's experiment indicate?

  There is a dense nucleus in atoms
• What was the significance of Rutherford's gold foil experiment?

  It led to the nuclear model of the atom
• What did scientists conclude about the charge of the nucleus?

  The nucleus must be positively charged
• Why is it important that the nucleus has a positive charge?

  To attract negatively charged electrons
• How did the concept of atomic structure change after Rutherford's findings?

  Atoms were understood to have a nucleus
• What did scientists realize about the majority of an atom's volume?

  It is mostly empty space
• What does the empty space in an atom signify?

  Electrons occupy regions around the nucleus
• What was the first nuclear model of the atom proposed by Rutherford?

  It described a dense nucleus with electrons
• What type of charge do alpha particles have?

  Positive charge
• Why do positive charges repel positive alpha particles?

  Because like charges repel each other
• What was the first nuclear model of the atom?

  The positive charge model
• What did the first nuclear model of the atom reveal?

  It revealed that atoms are mostly empty space
• Who developed the current model of the atom?

  Niels Bohr
• What did Niels Bohr propose about electrons?

  Electrons orbit the nucleus at certain distances
• What surrounds a positively charged nucleus?

  A cloud of negatively charged electrons
• What are energy levels in an atom?

  Distances where electrons orbit the nucleus
• What did James Chadwick prove in 1932?

  The existence of the neutron
• How did the discovery of the neutron affect atomic theory?

  It explained the mass imbalance in atoms
• What is the overall charge of the nucleus?

  Positive charge
• What particles make up the nucleus?

  Protons and neutrons
• How much smaller is the nucleus compared to the atom?

  About 10,000 times smaller
• What is the mass of the atom mostly made up of?

  The nucleus
• What charge do neutrons have?

  Neutral charge