Isotopes

• Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in shells
• The numbers of particles in an atom can be calculated from its atomic number and mass number
• Atom


  The smallest part of an element that can exist
• Element


  A substance made of one type of atom only
• Proton


  Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1
• Neutron


  Uncharged subatomic particle, with a mass of 1 relative to a proton. The relative charge of a neutron is 0
• Nucleus


  The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom
• Isotope


  Atoms of an element with the same number of protons and electrons but different numbers of neutrons
• Atomic number


  The number of protons in the nucleus of an atom. Also called the proton number
• Mass number


  The number of protons and neutrons found in the nucleus of an atom
• Isotopes of an element have the same atomic number but different mass numbers
• Isotopes of hydrogen


  • Hydrogen-1
  • Hydrogen-2
  • Hydrogen-3
• All three isotopes of hydrogen have identical chemical properties
• Relative atomic mass


  The mean relative mass of the atoms of the different isotopes in an element. It is the number of times heavier an atom is than one-twelfth of a carbon-12 atom
• Relative atomic masses are given in the periodic table and have the symbol Ar
• Mass numbers are always whole numbers, but relative atomic masses are often rounded to the nearest whole number and are not whole numbers
• The relative atomic mass of chlorine is 35.5 rather than a whole number because chlorine contains two different isotopes, chlorine-35 and chlorine-37
• Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in shells
• The numbers of particles in an atom can be calculated from its atomic number and mass number
• Relative atomic mass


  The mean relative mass of the atoms of the different isotopes in an element. It is the number of times heavier an atom is than one-twelfth of a carbon-12 atom
• Element


  A substance made of one type of atom only
• Mass number


  The number of protons and neutrons found in the nucleus of an atom
• Isotope


  Atoms of an element with the same number of protons and electrons but different numbers of neutrons
• Abundance


  If there is a lot of something, it is described as being abundant
• Calculating relative atomic mass of chlorine

  1. Chlorine naturally exists as two isotopes, chlorine-35 and chlorine-37

  2. The abundance of chlorine-35 is 75% and the abundance of chlorine-37 is 25%

  3. Relative atomic mass = (35 x 75 + 37 x 25) / (75 + 25) = 35.5
• Calculating relative atomic mass of copper

  1. Copper has two naturally-occurring isotopes with mass numbers 63 and 65

  2. The abundance of the 63 isotope is 69% and the abundance of the 65 isotope is 31%

  3. Relative atomic mass = (63 x 69 + 65 x 31) / (69 + 31) = 63.6