Isotopes

• isotopes


  Isotopes are different forms of the same element with same number of protons but different number of neutrons

  
• Ar values of elements

  These values tell you that magnesium atoms are twice as heavy as carbon atoms, and 24 times heavier than hydrogen atoms, while hydrogen atoms are 12 times lighter than carbon atoms. They also allow you to work out that three oxygen atoms weigh the same as two magnesium atoms.

  
• Calculating relative atomic mass - Higher tier

  Chlorine's Ar of 35.5 is an average of the masses of the different isotopes of chlorine. This is calculated by working out the relative abundance of each isotope. For example, in any sample of Chlorine 25% will be 37Cl and 75% 35Cl. The relative atomic mass is therefore calculated using the equation:

  
  

  (% of isotope 1 × mass of isotope 1) + (% of isotope 2 × mass of isotope 2) ÷ 100

  
  

  So in the case of chlorine:

  
  

  (75 × 35) + (25 × 37)∕100

  
  

  = 2625 + 925∕100

  
  

  = 35.3