history of the atom

• Structure of the Atom

  The structure of the atom has been developed over millennia as new experimental evidence was discovered and consequently the older models were changed and ultimately replaced
• New experimental evidence


  Changing or replacing old theories
• This is often due to advances in technology
• Only 15 years ago touch screen phones were not really a thing believe it or not
• Atomic Structure


  The atom contains 3 subatomic particles
• Subatomic particles


  • Proton
  • Neutron
  • Electron
• Proton


  • Relative Mass is 1
  • Relative Charge is +1
• Neutron


  • Relative Mass is 1
  • Relative Charge is 0
• Electron


  • Relative Mass is 1/2000
  • Relative Charge is -1
• As the alpha particle scattering experiment showed, most of the mass is concentrated in the nucleus (protons and neutrons)
• Dimensions of the Atom

  • Atoms are very very small, having a radius of ~ 0.1 nm (1 x 10-10 m)
  • The radius of a hair is far larger ~ 9 μm (9 x 10-6 m)
  • The atom is mainly empty space and thus the radius of the nucleus is 1/10 000 of the atom, 1 x 10-14 m
• Periodic Table


  • The top number which is also known as the atomic number, describes the number of nucleons (protons and neutrons) in the nucleus
  • Atoms of the same element have the same number of protons and electrons
  • Atoms of the same element can have different numbers of neutrons. These atoms are called isotopes
• Isotopes


  Atoms of the same element with differing numbers of neutrons but the same number of protons and electrons
• Different mass numbers, same atomic number – as this dictates the element