isotopes and relative atomic mass

• What do isotopes have different numbers of?

  Neutrons
• How is an element defined?

  Substance made of one type of atom
• What defines isotopes?

  Same protons, different neutrons
• What is true about most elements regarding isotopes?

  They are made of a mixture of isotopes
• What are the two main isotopes of chlorine?

  35Cl and 37Cl
• Why do isotopes have different mass numbers?

  Due to different numbers of neutrons
• What are the chemical properties of isotopes?

  • Same electron configuration
  • Same chemical properties (e.g. reactivity)
• What are the physical properties of isotopes?

  • Slightly different physical properties
  • Differences in mass and density
  • Depend on atomic mass
• How are relative masses of atoms measured?

  Compared to 1/12th carbon-12 mass
• What is relative isotopic mass?

  Mass of an isotope compared to carbon-12
• Is relative isotopic mass specific to what?

  A particular isotope of an element
• How is relative isotopic mass usually expressed?

  Close to a whole number
• How are relative isotopic masses rounded at A level?

  Rounded to one decimal place
• What are the relative isotopic masses of chlorine isotopes?

  35.0 and 37.0
• What is relative atomic mass (Ar)?

  Weighted mean mass of an atom
• How is relative atomic mass calculated?

  Weighted average of isotopes' masses
• Why is relative atomic mass not usually a whole number?

  It averages masses of all isotopes
• What is relative molecular mass (Mr)?

  Average mass of a molecule
• How is Mr calculated for simple covalent molecules?

  Add Ar values of all atoms
• What is relative formula mass used for?

  Used for ionic compounds
• How is relative formula mass calculated?

  Add Ar values of all ions
• How do you calculate Ar from isotopic abundances?

  • Use the formula for Ar calculation
  • Consider isotopic abundances
  • Average based on natural abundances