--- title: "Electron pair donor: the word “pair” is the mark - Kerfox" description: "AQA’s June 2018 Chemistry Paper 2 report says students who called a nucleophile an electron donor lost the mark. The missing word, and what else was refused." image: "https://www.kerfox.app/og.webp" url: "https://www.kerfox.app/blog/electron-pair-donor" --- [Kerfox](https://www.kerfox.app/) [THE KERFOX BLOG](https://www.kerfox.app/blog) THE MARK SCHEME WORD # Electron pair donor: the word “pair” is the mark A nucleophile is an electron pair donor. Drop the middle word and the sentence is still true of something, which is exactly why the board will not credit it. By [Eivan Kolchin](https://www.kerfox.app/about) 7 September 2026 ## The ruling In June 2018, question 2 of AQA’s A-level Chemistry Paper 2 asked students to explain a nucleophilic substitution. Most could say that the carbon-bromine bond was polar and that the carbon was slightly positive. The third marking point was for the nucleophile, and the report records what went wrong with it.[1](https://www.kerfox.app/blog/electron-pair-donor#source-1) AQA, A-LEVEL CHEMISTRY 7405/2, JUNE 2018, QUESTION 02.2 “Some students failed to gain mark point 3 as they referred to nucleophiles as electron donors rather than electron pair donors, or simply stated that the nucleophile was attracted to the slightly positive carbon atom.” Two refusals in one sentence. “Attracted to the carbon” is a description of where the nucleophile goes, not of what it is, and a definition mark is for the definition. “Electron donor” is closer, and it is the one worth understanding, because it is the answer of a student who knows the chemistry and has lost one word. ## What the pair is doing An electron donor, on its own, is a reducing agent: a species that hands over electrons to something else, one at a time if need be, and is oxidised in the process. Sodium is an electron donor. That is not what a nucleophile does, and the difference is the whole of the mechanism. A nucleophile brings a **pair** of electrons, together, and uses them to form a new covalent bond. The hydroxide ion attacking a halogenoalkane does not give up an electron. It shares two of its own with the carbon, and those two electrons become the new carbon-oxygen bond. The pair is the bond. Nothing is oxidised, nothing is reduced, and a student who writes “electron donor” has described a redox process that is not happening. That is why the word is not pedantry. “Electron pair donor” is a statement about bonding. “Electron donor” is a statement about redox. They are different claims, one of them is true of a nucleophile, and the mark scheme is written for the true one. ## The arrow starts on the pair Hydroxide attacking the carbon of a carbon-bromine bond. The first curly arrow leaves the lone pair, because the pair is what moves; the second leaves the bond and lands on the bromine. The same idea is drawn as well as written, and the board is as strict about the drawing. Five years later the June 2023 Paper 3 report restated the rule for every mechanism on the specification: “A curly arrow in any mechanism must always start either from the line representing a covalent bond or from a lone pair drawn on an atom.”[2](https://www.kerfox.app/blog/electron-pair-donor#source-2) Half the students scored full marks on that mechanism; the ones who did not had usually started an arrow from the wrong place. A curly arrow shows the movement of a pair of electrons. So it has to begin where a pair is: on a bond, or on a lone pair drawn as two dots. An arrow that starts on an atom’s symbol, or on the minus sign of the ion, or from empty space near the oxygen, is drawing something that has no electrons in it. The written definition and the drawn mechanism are the same fact twice, and both marks turn on the same word. ## The other names the paper refused The June 2018 report is a short catalogue of the same habit: a word next to the right one, credited as the wrong one.[1](https://www.kerfox.app/blog/electron-pair-donor#source-1) - **The name of the mechanism.** In question 7, on acyl chlorides, most students identified a correct reagent, “but ‘electrophilic addition’ and ‘reduction’ were frequent wrong answers for the name of the mechanism”. A mechanism’s name is a mark in its own right, and it is not interchangeable with the name of a different mechanism that also happens to involve a carbonyl. - **An observation, not a product.** In the next part, “a common error was to give the name of the product, i.e. ‘HCl gas’, rather than an observation as required, or alternatively to describe this as a ‘white precipitate’.” You cannot see hydrogen chloride. You can see misty fumes. And a gas is not a precipitate, whatever colour it is. - **Hydrogenation, not hydration.** In the benzene question, Level 3 answers were spoiled by “errors such as ‘hydration’ for hydrogenation”. Adding hydrogen and adding water are different reactions with names one syllable apart. - **Regenerated, not merely “not used up”.** On the chlorine radical, “some candidates wrote about Cl· acting as a catalyst and not being used up, without stating that it was regenerated/reformed”. A catalyst is not one that is never consumed; it is one that is consumed and remade, and the second half is the mark. - **A complete reagent.** For the nitrile-forming step, “some suggested the CN− ion, which is an incomplete reagent”. An ion is not something you can take from a bottle. Potassium cyanide is. The report also says, near its top, that several of its comments repeat advice printed in the mark scheme’s own instructions to examiners, and that this advice “should be known and understood by students”.[1](https://www.kerfox.app/blog/electron-pair-donor#source-1) That is the board telling you the rules are published and expecting you to have read them. ## Credited and refused All AQA, from the June 2018 Paper 2 and June 2023 Paper 3 reports. | Credited | Refused | Why the line is there | | electron pair donor | electron donor; “attracted to the δ+ carbon” | A nucleophile forms a bond with a pair of its own electrons. An electron donor is a reducing agent. June 2018 Q02.2. | | an arrow from a bond or a lone pair | an arrow from an atom, a charge or empty space | A curly arrow shows a pair of electrons moving, so it starts where a pair is. June 2023 Q02.5. | | nucleophilic addition-elimination | electrophilic addition; reduction | The mechanism’s name is its own mark and names a different mechanism if wrong. June 2018 Q07.2. | | misty fumes | HCl gas; white precipitate | An observation is what you see. A product name is not, and a gas is not a precipitate. June 2018 Q07.3. | | regenerated | “not used up” (alone) | A catalyst is consumed and remade; the remaking is the point. June 2018 Q01.4. | | potassium cyanide | CN− ion | A reagent is something you can take from a bottle. June 2018 Q02.4. | ## Sources 1. AQA (2018). Report on the Examination, A-level Chemistry 7405/2, June 2018. [filestore.aqa.org.uk/…/AQA-74052-WRE-JUN18.PDF](https://filestore.aqa.org.uk/sample-papers-and-mark-schemes/2018/june/AQA-74052-WRE-JUN18.PDF)Q02.2: students lost mark point 3 by calling nucleophiles electron donors rather than electron pair donors. Q07.2: "electrophilic addition" and "reduction" were frequent wrong names for the mechanism. Q07.3: "HCl gas", the name of a product, was given where an observation was required. Q06.1: "hydration" appeared for hydrogenation in Level 3 answers. 2. AQA (2023). Report on the Examination, A-level Chemistry 7405/3, June 2023. [filestore.aqa.org.uk/…/AQA-74053-WRE-JUN23.PDF](https://filestore.aqa.org.uk/sample-papers-and-mark-schemes/2023/june/AQA-74053-WRE-JUN23.PDF)Opens by naming lack of precision and "lack of clear application of chemical terminology" as the commonest reasons for lost marks. Q01.1: "proton donor" refused because the proton is accepted back later in the mechanism. Q01.2: a positive answer is needed, so "not with a Bunsen burner" scores nothing. Q01.5: two layers form because the liquids are immiscible, and the upper one is "less dense (NOT lighter)". Q01.6: "dehydration" refused for a drying agent because the term means something else in chemistry. ## Read next - [ THE MARK SCHEME WORD ### Less dense, not lighter: six words one chemistry paper refused AQA’s report on the June 2023 A-level Chemistry Paper 3 refuses six answers by name and gives its reasons. Each ruling, and the word to write instead. 7 September 2026 ](https://www.kerfox.app/blog/less-dense-not-lighter) - [ THE MARK SCHEME WORD ### Active site, binding site or receptor: the word AQA is waiting for An enzyme has an active site. An antibody has a binding site. A cell has a receptor. AQA’s examiner reports name the wrong one, four times, on three papers. 7 September 2026 ](https://www.kerfox.app/blog/active-site-is-not-the-answer) - [ HOW THE PAPER IS MARKED ### How a six-mark chemistry question is actually marked A levels-of-response answer is marked twice: for its shape, then for its content. What AQA’s examiners said a Level 3 answer looks like, and what holds it back. 7 September 2026 ](https://www.kerfox.app/blog/how-a-six-marker-is-marked) WHERE THIS IS BUILT IN Kerfox marks written answers against the board’s own words, so the word a mark scheme refuses is the word the app refuses too, with the reason. It is free, and it is in closed testing. [Join the waitlist](https://www.kerfox.app/waitlist)