Atomic structure exam tips

Exam tips

• Check the total number of electrons

  Always verify that the sum of electrons in the configuration equals the atomic number (or atomic number minus the ion charge).

  This quick check helps catch errors in subshell ordering or electron count.

• Use periodic trends to predict ionisation energies

  When asked about ionisation energies, refer to periodic trends to justify your answers.

  Understanding how ionisation energy varies across periods and down groups can help you make accurate predictions and explanations.

• Include units and sign when writing ionisation equations

  Always write the ionisation equation with the gaseous atom on the left, the cation on the right, and the electron as a separate species; include the energy value with the correct sign (positive) and units (kJ mol⁻¹).

  This ensures clarity and prevents confusion between energy input and output.

• Use ionisation‑energy trends to deduce electron configurations

  When given a set of ionisation energies, look for large jumps between successive values. A large jump indicates removal of an electron from a filled subshell, while a small jump indicates removal from the same subshell. This pattern helps you identify the subshells involved and thus the electron configuration.

  Exam questions often require you to interpret ionisation‑energy data; recognising the pattern of jumps is the quickest way to determine the configuration and to justify the existence of subshells.

• Use periodic trends to predict ionisation energies

  When asked about ionisation energies, refer to periodic trends such as atomic radius and nuclear charge.

  Understanding these trends will help you explain variations in ionisation energies effectively.