A-Level Chemistry: Atomic Structure

Atomic structure opens every A-Level Chemistry course, and its ideas — subshells, ionisation energies, mass spectrometry — echo through the whole two years. This quiz tests the topic at full A-level depth, where GCSE's simple shells give way to s, p and d subshells and the evidence that justifies them.

The electron-structure questions cover subshell energy ordering and capacities, and the two classic Period 3 anomalies every exam paper loves: the dip between magnesium and aluminium (the 3p electron sitting higher in energy than 3s) and the dip between phosphorus and sulfur (paired-electron repulsion in 3p). Ionisation energy is examined from three angles: the factors driving the general increase across a period, the group trend down Group 2, and — the most exam-typical skill — reading a set of successive ionisation energies (578, 1817, 2745, then a jump to 11577) to deduce which group an element belongs to from the position of the great leap.

Mass spectrometry gets the full time-of-flight treatment: the requirements of electron impact ionisation (vaporised sample, high-energy electron beam), what actually happens at the detector — positive ions gaining electrons to generate a current proportional to abundance — and a relative atomic mass calculation from isotopic abundances worked to one decimal place.

One question was tightened during verification so that the ionisation-method options are unambiguous, and every numeric answer has been independently recomputed. The explanations consistently connect observation to theory — why the jump in successive ionisation energies means a new shell, why the current at the detector measures abundance — which is precisely the explain-the-evidence register A-level papers mark in.

• Write electron configurations with s, p and d subshells and explain their energy order
• Explain the Mg→Al and P→S ionisation energy dips
• Deduce an element's group from successive ionisation energy jumps
• Describe time-of-flight mass spectrometry from ionisation to detection
• Calculate relative atomic mass from isotopic abundances

Aligned to the physical chemistry core of the DfE A level science subject content as delivered in current specifications: electron configuration, ionisation energy trends and their evidence, time-of-flight mass spectrometry, and relative atomic mass calculations.