2.1.1 & 2.1.2

• What does the atomic number, Z, represent in an atom?

  The number of protons in the nucleus
• What is the mass number, A, of an atom?

  The total number of protons and neutrons in the atom
• How do you calculate the number of neutrons in an atom?

  Number of neutrons = A - Z
• What are isotopes and their properties?

  • Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.
  • They have similar chemical properties due to the same electronic structure.
  • They may have slightly varying physical properties because of different masses.
• What is the definition of relative isotopic mass?

  The mass of one isotope compared to one twelfth of the mass of one atom of carbon-12
• How is relative atomic mass defined?

  The weighted mean mass of one atom compared to one twelfth of the mass of one atom of carbon-12
• What does relative molecular mass represent?

  The average mass of a molecule compared to one twelfth of the mass of one atom of carbon-12
• How do you calculate relative atomic mass (R.A.M)?

  1. A.M =
• What is another formula for calculating relative atomic mass (R.A.M)?

  1. A.M =
• state two differences between isotopes of the same element 


  • different numbers of neutrons
  • different physical properties
• state why different isotopes of the same element have the same chemical properties 


  same number of e- in outer shell