P6 - Atoms

• Atom

  • Nucleus containing protons and neutrons, around which electrons orbit in fixed energy levels/shells
• Plum pudding model of the atom

  Sphere of positive charge with negative electrons embedded in it
• Charges of subatomic particles

  • Protons: positive
  • Neutrons: no charge
  • Electrons: negative
• Atoms have no overall charge because they have equal numbers of positive protons and negative electrons
• Radius of an atom

  Around 1 x 10 to the power of -10 meters
• Nucleus is around 10000 times smaller than the whole atom
• How an electron can move up an energy level

  Absorb sufficient electromagnetic radiation
• Ionisation

  Process which adds or removes electrons from an atom
• Positive ion

  Atom that has lost an electron
• Negative ion

  Atom that has gained one or more electrons
• Atomic number

  Number of protons in one atom of the element
• Mass number

  Number of protons plus number of neutrons
• Atoms of the same element always have the same number of protons
• Isotopes

  Atoms of the same element with different numbers of neutrons
• The two main conclusions from the alpha particle scattering experiment were: 1) Most of the mass of an atom is concentrated in the nucleus, 2) The nucleus is positively charged