Atomic structure

• Atom


  The smallest piece of an element that can exist
• Molecule


  Formed when atoms join together by chemical bonds (can be made of atoms of the same element)
• Subatomic particles


  • Proton
  • Neutron
  • Electron
• Proton


  Relative mass: 1, Relative charge: +1, Position: in the nucleus
• Neutron


  Relative mass: 1, Relative charge: 0, Position: in the nucleus
• Electron


  Relative mass: 1/1836, Relative charge: -1, Position: in shells around nucleus
• Atomic (proton) number


  Number of protons (= number of electrons if it's an atom, because atoms are neutral)
• Mass (nucleon) number


  Number of protons + neutrons
• Isotopes


  Different atoms of the same element containing the same number of protons but different numbers of neutrons in their nuclei
• Relative atomic mass (Ar)


  An average value that takes account of the abundance of the isotopes of the element
• Calculating relative atomic mass (Ar) from isotopic abundances

  1. Multiply mass of isotope-A by % of isotope-A

  2. Multiply mass of isotope-B by % of isotope-B

  3. Add the two results

  4. Divide by 100