developing the model of the Atom

• Who first proposed the idea of "atomos"?

  Democritus
• What did Democritus believe about matter?

  All matter is made of identical lumps
• What did John Dalton agree with Democritus?

  Atoms are tiny spheres that can't be broken
• How did Dalton's view of atoms differ from Democritus's?

  Dalton believed each element had different atoms
• Who discovered electrons?

  1. J. Thomson
• What did Thomson's plum pudding model suggest?

  Atoms are positive spheres with negative electrons
• What was the purpose of the alpha scattering experiment?

  To test the plum pudding model of the atom
• What did scientists expect from the alpha particles in the experiment?

  They expected particles to pass through or slightly deflect
• What was the unexpected result of the alpha scattering experiment?

  Some particles were deflected back unexpectedly
• What conclusion did scientists draw from the deflection of alpha particles?

  Most mass is concentrated in a tiny nucleus
• What charge does the nucleus of an atom have?

  The nucleus has a positive charge
• What is the first nuclear model of the atom based on?

  Alpha particle scattering experiment results
• What did Bohr add to the nuclear model of the atom?

  Electrons orbit at certain energy levels
• How did Bohr's calculations relate to experimental data?

  His calculations agreed with experimental data
• What did further experiments reveal about the nucleus?

  The nucleus is made of protons with positive charge
• Who proved the existence of the neutron?

  James Chadwick
• What does the neutron explain in atomic structure?

  The imbalance between atomic and mass numbers
• What makes up most of the mass of an atom?

  The nucleus
• What is the relative charge of protons?

  +1
• What is the relative charge of neutrons?

  0
• What is the relative charge of electrons?

  -1
• How much smaller is the nucleus compared to the atom?

  100,000 times smaller
• What is the approximate radius of an atom?

  $1 \times 10^{-10} \text{ m}$
• What does the current atomic model suggest about its stability?

  It may change with new experiments
• What is true about the number of protons and electrons in an atom?

  They are equal in number
• Why do atoms have no overall charge?

  Protons and electrons have equal but opposite charges
• What happens to electrons when they gain energy?

  They move to a higher energy level
• What occurs when electrons release energy?

  They move to a lower energy level
• What happens if outer electrons leave the atom?

  The atom becomes a positively charged ion
• What are the key components of the current atomic model?

  • Tiny nucleus at the center
  • Contains protons (+1 charge) and neutrons (0 charge)
  • Surrounded by negative electrons (-1 charge)
  • Most of the atom is empty space
• What are the historical developments in the atomic model?

  1. Democritus: "atomos" concept
  2. Dalton: Atoms as indivisible spheres
  3. Thomson: Plum pudding model with electrons
  4. Rutherford: Nuclear model from alpha scattering
  5. Bohr: Energy levels for electron orbits
  6. Chadwick: Discovery of the neutron