Atomic Structure

• Nucleus - where protons and neutrons are located
• Shell - where electrons are found
• Protons - positively charged particles with a relative mass of 1
• Neutrons - neutral charge, relative mass of 1
• Electrons - negatively charged, relative mass 0.0005
• Number of protons = atomic number
• Number of protons = number of electrons
• Mass number = protons + neutrons
• Group number = number of electrons on the outer shell
• Electronic configuration = 2,8,8 ect..
• Ion - created when an atom gains or loses an electron
• Metal atoms lose electrons to become positively charged ions
• Non-metal atoms gain electrons to become negatively charged ions
• Isotopes - different forms of the same element with the same number of protons but different number of neutrons
• RAM = (isotope 1 x abundance) + (isotope 2 x abundance) / abundance of all isotopes (100)
• John Dalton, 1803 - all substances are made of small spheres called atoms, new substances are formed by adding atoms and rearranging atoms
• JJ Thompson, 1897 - plum pudding model, negatively charged particles (electrons) embedded in a ball of positive charge
• Neils Bohr, 1913 - showed with the heating of atoms that if the electrons were in a cloud the atom would collapse in on itself, concluded electrons orbited the nucleus in shells
• James Chadwick, 1932 - nuclear model, proved neutrally charged particles (neutrons) lived in the nucleus
• Earnest Rutherford, 1909-1911 - Positively charged alpha particles were fired at a thin sheet of gold inside a vacuum. Observation: Most alpha particles passed through the foil.

  • Conclusion: The atom is mostly empty space.
  • Observation: Some alpha particles were deflected at large angles.
  • Conclusion: There is a concentrated positive charge in the atom (the nucleus).
  • Observation: A few alpha particles bounced straight back.
  • Conclusion: The positive charge and mass are concentrated in a tiny central nucleus.