Fundamental Particles

• What holds electrons and protons together in an atom?

  Electrostatic forces
• How do electrostatic forces compare to strong nuclear forces?

  Electrostatic forces are weaker
• What is the maximum number of electrons in the first four shells of an atom?

  • 1st shell: 2 electrons
  • 2nd shell: 8 electrons
  • 3rd shell: 18 electrons
  • 4th shell: 32 electrons
• What does the atomic number represent?

  Number of protons in the nucleus
• What is the mass number of an atom?

  Sum of protons and neutrons in the nucleus
• What determines the chemical properties of an atom?

  Number of electrons in the outer shell
• How is relative atomic mass (Ar) defined?

  Mean mass of an atom of an element
• What is the reference for relative atomic mass?

  1/12th mass of one atom of carbon-12
• How is relative molecular mass (Mr) defined?

  Mean mass of a molecule
• What is the reference for relative molecular mass?

  1/12th mass of one atom of carbon-12
• How is the average relative atomic mass calculated for isotopes?

  Average Ar =

  (Isotope 1 abundance x mass) +

  (Isotope 2 abundance x mass) /

  Sum of abundances