Atomic structure and the Periodic Table

Sample questions

Original practice questions written in the style of the exam.

1. Question 13 marks

   The mass spectrum of a sample of an element shows two peaks:

   $m/z$	relative abundance
   69	15.2
   71	10.1

   Calculate the relative atomic mass of the element to 1 decimal place and use the Periodic Table to identify it.

   Mark scheme

   • Multiplies each $m/z$ by its abundance and adds: $(69 \times 15.2) + (71 \times 10.1) = 1765.9$ (1)
   • Divides by the total abundance: $1765.9 \div 25.3$ (1)
   • $A_r = 69.8$, so the element is gallium (Ga) (1)
2. Question 23 marks

   The first four successive ionisation energies of element X, in $\text{kJ mol}^{-1}$, are:

   $738 \qquad 1451 \qquad 7733 \qquad 10\,541$

   Deduce the group of the Periodic Table that contains X. Explain your reasoning.

   Mark scheme

   • There is a large jump between the second and third ionisation energies (1)
   • So X has two electrons in its outer shell and is in Group 2 (1)