1. 1
   A teacher shows students a table describing the three sub-atomic particles: protons and neutrons, each with a relative mass of about 1, and electrons, which are far lighter.

   (a)

   A teacher tells students that protons and neutrons each have a relative mass of about 1. What is the relative mass of an electron compared with a proton?

   [1 mark]

   • AVery small, much less than 1
   • BExactly 1, the same as a proton
   • CAbout 2, twice that of a proton
   • DExactly 0, electrons have no mass at all

   (b)

   What is the relative mass of a neutron?

   [1 mark]

   • A0
   • B1
   • C−1
   • DVery small, close to 0

   (c)

   Explain why almost all of the mass of an atom comes from its nucleus, rather than from its electrons.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A textbook explains that the relative atomic mass of every element is worked out by comparing the mass of its atoms with a chosen reference isotope, and that this value is an average across all the naturally occurring isotopes of that element.

   (a)

   The relative atomic mass scale used in chemistry is based on comparing atoms with a particular isotope. Which isotope is this?

   [1 mark]

   • ACarbon-14
   • BHydrogen-1
   • COxygen-16
   • DCarbon-12

   (b)

   Which statement best defines relative atomic mass ($A_r$)?

   [1 mark]

   • AThe number of protons in an atom of the element
   • BThe exact mass, in grams, of a single atom of the element
   • CAn average value comparing the mass of atoms of an element with the mass of carbon-12 atoms
   • DThe mass number of the least common isotope of the element

   (c)

   Explain why relative atomic mass is described as an 'average' value.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Chlorine exists naturally as a mixture of two isotopes, one with mass number 35 and one with mass number 37, present in different proportions. The relative atomic mass of chlorine is 35.5.

   (a)

   Explain why the relative atomic mass of chlorine is not a whole number.

   [3 marks]

   (b)

   Explain how the different proportions in which the two chlorine isotopes occur naturally lead to a relative atomic mass of 35.5, which is much closer to 35 than to 37.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A scientist is explaining why the relative atomic mass of an element, such as chlorine with a value of 35.5, is not simply equal to the mass number of its most common isotope, and how this relates to the masses of the particles making up its atoms.

   (a)

   Explain the relative masses of protons, neutrons and electrons, and describe why the mass of an atom is considered to come almost entirely from its nucleus.

   [6 marks]

   (b)

   Explain what relative atomic mass represents, and explain why it is not simply equal to the mass number of the most common isotope of an element.

   [6 marks]

   Total for question 4: 12 marks

End of questions