atoms

• What is the modern model of the atom based on?

  Evidence from experiments over time
• How might future experiments affect our understanding of the atom?

  They may alter or replace the current model
• How did John Dalton view the atom?

  As a solid sphere that cannot be divided
• What key particles did Dalton's model not include?

  Protons, neutrons, or electrons
• What did the discovery of electrons lead to?

  The plum pudding model of the atom
• Describe the plum pudding model of the atom.

  A cloud of positive charge with electrons embedded
• What was the purpose of the alpha scattering experiment?

  To study the structure of the atom
• What did scientists expect to happen in the alpha scattering experiment?

  Alpha particles would travel straight through gold
• What was surprising about the results of the alpha scattering experiment?

  Some alpha particles bounced back and were deflected
• What did scientists conclude about the atom's structure from the alpha scattering experiment?

  The positive charge and mass are concentrated in the nucleus
• What model replaced the plum pudding model?

  The nuclear model
• How do electrons behave in the nuclear model?

  They orbit the nucleus but not at set distances
• Who improved the nuclear model of the atom?

  Niels Bohr
• What did Bohr calculate about electron orbits?

  Electrons orbit the nucleus at fixed distances
• What are the orbits of electrons called in Bohr's model?

  Shells or energy levels
• What evidence did later experiments provide about the nucleus?

  The positive charge could be split into smaller particles
• What are positively charged particles in the nucleus called?

  Protons
• Who discovered the neutron?

  James Chadwick
• What is the charge of a neutron?

  It has no charge
• Where are protons and neutrons located in an atom?

  In the nucleus
• What is the radius of the nucleus compared to an atom?

  10,000 times smaller than the atom
• What does the nucleus contain?

  Protons and neutrons
• Where is most of the mass of an atom concentrated?

  In the nucleus
• How do electrons orbit the nucleus?

  At different fixed distances called energy levels
• How can electrons gain energy?

  By absorbing electromagnetic radiation
• What happens when electrons lose energy?

  They move to a lower energy level
• What is ionization?

  Atoms become charged by losing or gaining electrons
• What forms a positive ion?

  An uncharged atom loses one or more electrons
• What forms a negative ion?

  An uncharged atom gains one or more electrons