Elements, Isotopes & Relative Atomic Mass

• What are isotopes?

  Isotopes are atoms with the same atomic number, but different mass  numbers.
• What are isotopes?

  Isotopes are atoms with the same number of protons, but different numbers of neutrons
• An atom has 13 protons and 14 neutrons. What is its mass number?

  Mass number is the total number of protons and neutrons. So in this case we just do 13 + 14 = 27
• What are isotopes?

  Atoms of the same element with different numbers of neutrons
• Four atoms have the numbers of protons and neutrons given below. Which two atoms are isotopes of the same element?

  Atom W: 11 protons and 10 neutrons

  Atom X: 10 protons and 10 neutrons

  Atom Y: 9 protons and 9 neutrons

  Atom Z: 10 protons and 9 neutrons

  X and Z
• Lithium naturally exists as two isotopes: lithium-6, with an abundance of 7.6%, and lithium-7, with an abundance of 92.4%.

  What is the relative atomic mass of lithium?


  6.92
• Uranium-235 has 92 protons. How many neutrons does it have?

  143

  The 235 of Uranium-235 tells us that the mass number is 235. So to find the number of neutrons we do 235 - 92 = 143.
• What is an element symbol?


  An element symbol is a one or two letter abbreviation for a chemical element's name
• What is the formula for relative atomic mass?

  Relative Atomic mass (Ar) = isotope abundance x isotope mass number/sum of abundance of all isotopes
• What does relative atomic mass mean?

  Relative atomic mass is the average mass of all the isotopes of an element, taking into account the abundance and mass number of each isotope.
• Approximately how many different elements are there?

  There are approximately 100 different elements.
• What is an element?


  An element is a substance made up of only one type of atom, so where all the atoms of a substance have the same number of protons.