Edexcel International A Level Chemistry: Preparing for Six Units and Two Practical Skills Papers

Edexcel International A Level Chemistry (YCH11) is modular, with three International Advanced Subsidiary units and three International A2 units, all externally assessed. Unit 1 (Structure, Bonding and Introduction to Organic Chemistry) and Unit 2 (Energetics, Group Chemistry, Halogenoalkanes and Alcohols) are each 1 hour 30 minutes, 80 marks and 20%. Unit 4 (Rates, Equilibria and Further Organic Chemistry) and Unit 5 (Transition Metals and Organic Nitrogen Chemistry) are each 1 hour 45 minutes, 90 marks and 20%. Units 3 and 6 – Practical Skills in Chemistry I and II – are each 1 hour 20 minutes, 50 marks and 10%, and are written papers rather than hands-on laboratory assessments. The specification states that at least 20% of marks overall target Level 2 mathematics or above. These notes complement the site’s guides to Structure, Bonding and Introduction to Organic Chemistry and Atomic Structure and Mass Spectrometry.

The practical skills units are written examinations of experimental thinking

Units 3 and 6 are 20% of the qualification between them and are sat as written papers. They assess planning, apparatus choice, uncertainty, error, and the interpretation and evaluation of results. Exam-preparation priority: revise them as content. For every core practical, be able to write from memory what was measured, what was controlled, what the principal source of uncertainty was, and how the method could be improved to address that specific uncertainty.

A stated 20% of marks target mathematics – know which mathematics

Twenty per cent of the qualification’s marks are mathematical, and in chemistry that means a predictable set of skills: moles and concentration, titration calculations, enthalpy changes, rate equations and orders, equilibrium constants, and percentage yield and atom economy. Exam-preparation priority: drill these specifically and to speed. They are among the most reliably scorable marks on the whole specification, and they are lost far more often to unfamiliarity with the arithmetic than to misunderstanding of the chemistry.

Organic chemistry accumulates – Unit 5 assumes Units 1, 2 and 4

Organic content runs through four of the six units, each adding reactions and mechanisms to what came before. Exam-preparation priority: maintain a single, cumulative reaction map rather than separate notes per unit – reagent, conditions, product, mechanism type – and keep adding to it. Candidates who revise Unit 5’s organic content in isolation routinely cannot complete a synthesis question that requires a Unit 2 step.

Mechanisms are marked on the detail, not the idea

Curly arrows must start from the right place (a lone pair or a bond) and end at the right place; charges, dipoles and intermediates must be shown. Exam-preparation priority: practise drawing mechanisms out by hand repeatedly. Recognising a mechanism when you see it is not the same skill as producing it accurately under time pressure, and only the second one is examined.

The A2 papers are longer and denser than the AS papers

Units 4 and 5 give 105 minutes for 90 marks, against 90 minutes for 80 at AS. Exam-preparation priority: practise complete A2 papers to time, because the extra content per paper is greater than the extra time allowed.

Worked routine: answering an organic mechanism question

The routine below is an original model written for this resource, not a reproduction of any official past paper or mark scheme.

Step 1 - identify the reagent type and therefore the mechanism:
Nucleophile, electrophile or radical? The reagent tells you the
mechanism class before you draw anything.

Step 2 - mark the electron-rich and electron-poor centres:
Show the dipole or the lone pair on the structure. This is often
directly creditable.

Step 3 - draw arrows FROM electron density TO the electron-poor
centre:
An arrow starting at an atom rather than at a lone pair or a bond
is a common and costly error.

Step 4 - show intermediates and charges explicitly:
Carbocations, carbanions and their charges are separate marks.

Step 5 - state reagents and conditions alongside the mechanism:
Reagent, solvent, temperature, catalyst. Conditions are frequently
worth marks the mechanism itself does not carry.

Step 3 is where most mechanism marks are lost. The arrow convention is a rule about electron movement, and marks follow the convention rather than the plausibility of the product.

Before/during exam checklist

• Before the exams: revise Units 3 and 6 as examinable written content, with a written note per core practical (measured, controlled, main uncertainty, targeted improvement); drill the recurring calculations to speed; maintain one cumulative organic reaction map across all units; practise drawing mechanisms by hand.
• During A2 papers: allow for the higher content density relative to the extra time.
• In every calculation: show the relationship before substituting, and check significant figures.
• In every mechanism: identify the mechanism class from the reagent, mark electron density, draw arrows from a lone pair or bond, show intermediates and charges, and state conditions.

Self-test

1. What are Units 3 and 6, and what do they actually assess?
2. What proportion of marks targets Level 2 mathematics, and which calculations does that mean?
3. Why should organic notes be cumulative rather than per unit?
4. What is the most common way mechanism marks are lost?

Answers: 1. Practical Skills in Chemistry I and II – written papers, 10% each, assessing planning, apparatus choice, uncertainty, error and the interpretation and evaluation of results rather than manipulative technique. 2. At least 20% overall, which in practice means moles and concentration, titrations, enthalpy changes, rates and orders, equilibrium constants, and yield and atom economy. 3. Because organic content runs through four units and accumulates – a Unit 5 synthesis question frequently requires a reaction first met in Unit 2. 4. Arrows drawn from an atom rather than from a lone pair or a bond, and omitted charges or intermediates – the marks follow the electron-movement convention.

Written against the Pearson Edexcel International Advanced Level Chemistry specification (official specification PDF, verified 2026-08-28). The mechanism routine above is an original model written for this resource, not a reproduction of any official past paper or mark scheme. Always check the current specification for your examination series at qualifications.pearson.com.