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<title>DP Chemistry: 'Curly arrows'</title>
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<meta name="description" content="The correct use of curly arrows can cause real problems – both to students (and teachers) and examiners. The main reason why students fail to score marks is that they use the arrows completely wrongly but even when arguably they have been used correctly students can still fail to score marks depending on how examiners interpret the markscheme. What I hope to show is how you can use them correctly so that you can be...">
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href="../19287/proteins-enzymes--1.html">Proteins & enzymes </a></li><li><a href="../19291/lipids-1.html">Lipids</a></li><li><a href="../19299/carbohydrates--1.html">Carbohydrates </a></li><li><a href="../19305/vitamins--1.html">Vitamins </a></li><li><a href="../19313/biochemistry-the-environment--1.html">Biochemistry & the environment </a></li><li><a href="../19336/proteins-enzymes-ahl--1.html">Proteins & enzymes (AHL) </a></li><li><a href="../19347/nucleic-acids--1.html">Nucleic acids </a></li><li><a href="../19361/biological-pigments--1.html">Biological pigments </a></li><li><a href="../19366/stereochemistry-in-biomolecules-1.html">Stereochemistry in biomolecules</a></li></ul></li><li><a href="../19390/option-c--1.html" class="father">Option C </a><ul class="level-2"><li><a href="../19391/energy-sources-1.html">Energy sources</a></li><li><a href="../19407/fossil-fuels-1.html">Fossil fuels</a></li><li><a href="../19411/nuclear-fusion-nuclear-fission-reactions-1.html">Nuclear fusion & nuclear fission reactions</a></li><li><a href="../19429/solar-energy-1.html">Solar energy</a></li><li><a href="../19437/environmental-impact-global-warming-1.html">Environmental impact - global warming</a></li><li><a href="../19453/electrochemistry-rechargeable-batteries-fuel-cells-1.html">Electrochemistry, rechargeable batteries & fuel cells</a></li><li><a href="../19458/nuclear-fusion-fission-hl--1.html">Nuclear fusion & fission (HL) </a></li><li><a href="../19470/photovoltaic-cells-and-dsscs-1.html">Photovoltaic cells and DSSCs</a></li></ul></li><li><a href="../19078/option-d-1.html" class="father">Option D</a><ul class="level-2"><li><a href="../19079/pharmaceutical-products-drug-action--1.html">Pharmaceutical products & drug action </a></li><li><a href="../19158/aspirin-penicillin--1.html">Aspirin & penicillin </a></li><li><a href="../19174/opiates-1.html">Opiates</a></li><li><a href="../19184/ph-regulation-of-the-stomach-1.html">pH regulation of the stomach</a></li><li><a href="../19194/antiviral-medications--1.html">Antiviral medications </a></li><li><a href="../19211/environmental-impact-of-some-medications-1.html">Environmental impact of some medications</a></li><li><a href="../19254/taxol-a-chiral-auxiliary-case-study-1.html">Taxol - a chiral auxiliary case study</a></li><li><a href="../19258/nuclear-medicine--1.html">Nuclear medicine </a></li><li><a href="../19273/drug-detection-analysis--1.html">Drug detection & analysis </a></li></ul></li></ul></li><li><a href="../16592/practical-scheme-of-work-ia--1.html">Practical scheme of work & IA </a><ul class="level-1"><li><a href="../16682/internal-assessment-1.html" class="father">Internal Assessment</a><ul class="level-2"><li><a href="../18892/scaffolding-the-investigation-1.html">'Scaffolding' the investigation</a></li><li><a href="../18896/timing-organisation--1.html">Timing & organisation </a></li><li><a href="../18905/choosing-the-research-question-1.html">Choosing the research question</a></li><li><a href="../18946/personal-engagement-1.html">Personal engagement</a></li><li><a href="../18950/exploration-1.html">Exploration</a></li><li><a href="../18957/analysis-1.html">Analysis</a></li><li><a href="../18965/evaluation-1.html">Evaluation</a></li><li><a href="../18966/communication-1.html">Communication</a></li><li><a href="../19882/internal-standardization-of-the-ia-1.html">Internal standardization of the IA</a></li><li><a href="../19901/submitting-the-samples-for-moderation-2.html">Submitting the samples for moderation</a></li><li><a href="../33754/ten-suggestions-for-ias-using-secondary-data-1.html">Ten suggestions for IAs using secondary data</a></li><li><a href="../37544/gaining-full-marks-for-a-databased-ia--1.html">Gaining full marks for a databased IA </a></li><li><a href="../19506/ia-example-marking-exercise--1.html">IA example & marking exercise </a></li><li><a href="../23929/genuine-examples-of-moderated-ia-reports-1.html">Genuine examples of moderated IA reports</a></li><li><a href="../25234/examples-of-teacher-marked-ia-reports--1.html">Examples of teacher-marked IA reports </a></li><li><a href="../37542/history-of-internal-assessment-1.html">History of Internal Assessment</a></li></ul></li><li><a href="../16598/mandatory-laboratory-components-1.html" class="father">Mandatory laboratory components</a><ul class="level-2"><li><a href="../16613/formula-of-magnesium-oxide--1.html">Formula of magnesium oxide </a></li><li><a href="../16612/determining-the-mr-of-an-unknown-gas-1.html">Determining the <i>M</i><sub>r</sub> of an unknown gas</a></li><li><a href="../16615/acid-base-titrations--1.html">Acid-base titrations </a></li><li><a href="../16616/a-green-acid-base-practical-1.html">A green acid-base practical</a></li><li><a href="../16617/analysis-of-aspirin-tablets-1.html">Analysis of aspirin tablets</a></li><li><a href="../16618/caco3-in-egg-shells-1.html">CaCO<sub>3</sub> in egg shells</a></li><li><a href="../16644/enthalpy-changes-1.html">Enthalpy changes</a></li><li><a href="../16631/reaction-rates-1.html">Reaction rates</a></li><li><a href="../16635/rate-dependent-factors-1.html">Rate-dependent factors</a></li><li><a href="../16636/determining-ea-for-a-reaction-1.html">Determining <i>E</i><sub>a</sub> for a reaction</a></li><li><a href="../16637/iodination-of-propanone-1.html">Iodination of propanone</a></li><li><a href="../18144/titrations-with-a-ph-meter-1.html">Titrations with a pH meter</a></li><li><a href="../18355/redox-titration-with-kmno4--1.html">Redox titration with KMnO<sub>4</sub> </a></li><li><a href="../16640/voltaic-cells-1.html">Voltaic cells</a></li><li><a href="../16659/3-d-molecular-modelling--1.html">3-D molecular modelling </a></li></ul></li><li><a href="../17168/other-good-practicals-1.html" class="father">Other good practicals</a><ul class="level-2"><li><a href="../17196/common-chemical-reactions-1.html">Common chemical reactions</a></li><li><a href="../227/elements-oxides-of-the-third-period--1.html">Elements & oxides of the third period </a></li><li><a href="../17239/the-halogens-1.html">The halogens</a></li><li><a href="../17162/boiling-points-of-mixtures-1.html">Boiling points of mixtures</a></li><li><a href="../17170/polarity-of-molecules-1.html">Polarity of molecules</a></li><li><a href="../18083/le-chateliers-principle--1.html">Le Chatelier's principle </a></li><li><a href="../19582/determining-kc-for-an-esterification-reaction-1.html">Determining <i>K</i><sub>c</sub> for an esterification reaction</a></li><li><a href="../18164/redox-reactions-of-vanadium--1.html">Redox reactions of vanadium </a></li><li><a href="../18351/chlorine-in-swimming-pools--1.html">Chlorine in swimming pools </a></li><li><a href="../18178/analysis-of-cuii-ions-in-solution--1.html">Analysis of Cu(II) ions in solution </a></li><li><a href="../18179/percentage-of-copper-in-brass-1.html">Percentage of copper in brass</a></li><li><a href="../18356/electrolytic-cells--1.html">Electrolytic cells </a></li><li><a href="../18598/reactions-of-organic-compounds-1.html">Reactions of organic compounds</a></li><li><a href="../18752/hydrolysis-of-halogenoalkanes-1.html">Hydrolysis of halogenoalkanes</a></li><li><a href="../18784/preparation-of-13-dinitrobenzene--1.html">Preparation of 1,3-dinitrobenzene </a></li><li><a href="../19022/determination-of-an-organic-structure-1.html">Determination of an organic structure</a></li><li><a href="../19887/preparation-of-nylon-66-1.html">Preparation of nylon 6,6</a></li><li><a href="../19343/determination-of-vitamin-c-content--1.html">Determination of vitamin C content </a></li><li><a href="../19342/hydrolysis-of-starch--1.html">Hydrolysis of starch </a></li><li><a href="../19159/preparation-purification-of-aspirin--1.html">Preparation & purification of aspirin </a></li></ul></li><li><a href="../18851/ict-in-practical-work-1.html" class="father">ICT in practical work</a><ul class="level-2"><li><a href="../18852/data-logging--1.html">Data logging </a></li><li><a href="../18853/software-for-graph-plotting--1.html">Software for graph plotting </a></li><li><a href="../18854/spreadsheets-for-data-processing--1.html">Spreadsheets for data processing </a></li><li><a href="../18855/databases-1.html">Databases</a></li><li><a href="../18856/computer-modelling-simulations--1.html">Computer modelling & simulations </a></li></ul></li><li><a href="../16594/group-4-project-1.html" class="father">Group 4 Project</a><ul class="level-2"><li><a href="../16595/practicalities-1.html">Practicalities</a></li><li><a href="../16596/reflective-statement--2.html">Reflective statement </a></li></ul></li><li><a href="../16666/a-new-laboratory-1.html">A new laboratory?</a></li></ul></li><li><a href="../16284/exams-1.html">Exams</a><ul class="level-1"><li><a href="../16286/essential-facts-1.html" class="father">Essential Facts</a><ul class="level-2"><li><a href="../16287/objectives-command-terms-1.html">Objectives & command terms</a></li><li><a href="../16288/grade-descriptors-1.html">Grade descriptors</a></li><li><a href="../16289/grade-boundaries-1.html">Grade boundaries</a></li></ul></li><li><a href="../16302/paper-1-multiple-choice-1.html" class="father">Paper 1 (Multiple Choice)</a><ul class="level-2"><li><a href="../16303/advice-to-students-paper-1-1.html">Advice to students (Paper 1)</a></li><li><a href="../31515/practice-paper-1-exams-1.html">Practice Paper 1 exams</a></li></ul></li><li><a href="../16305/paper-2-1.html" class="father">Paper 2</a><ul class="level-2"><li><a href="../16306/advice-to-students-paper-2-1.html">Advice to students (Paper 2)</a></li><li><a href="../16307/areas-of-difficulty-1.html">Areas of difficulty</a></li></ul></li><li><a href="../16313/paper-3--1.html" class="father">Paper 3 </a><ul class="level-2"><li><a href="../16314/advice-to-students-paper-3-1.html">Advice to students (Paper 3)</a></li><li><a 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href="../3147/ib-core-1.html">IB Core</a><ul class="level-1"><li><a href="../3149/learner-profile-1.html">Learner Profile</a></li><li><a href="../21735/extended-essays--1.html" class="father">Extended Essays </a><ul class="level-2"><li><a href="../21736/overview--1.html">Overview </a></li><li><a href="../21780/responsibilities-1.html">Responsibilities</a></li><li><a href="../21790/resources-1.html">Resources</a></li><li><a href="../21800/research-1.html">Research</a></li><li><a href="../21804/writing-the-essay-1.html">Writing the essay</a></li><li><a href="../21810/assessment-1.html">Assessment</a></li><li><a href="../22434/summary-of-advice--1.html">Summary of advice </a></li><li><a href="../25272/faqs--1.html">FAQs </a></li></ul></li><li><a href="../307/theory-of-knowledge-tok-1.html" class="father">Theory of Knowledge (TOK)</a><ul class="level-2"><li><a href="../41171/the-12-tok-concepts-1.html">The 12 TOK concepts</a></li><li><a href="../3507/why-tok-chemistry-1.html">Why TOK & Chemistry?</a></li><li><a href="../3505/a-modern-paradigm-1.html">A modern paradigm</a></li></ul></li></ul></li><li><a href="../17783/fast-track-to-tests-questions-1.html">Fast track to tests & questions</a><ul class="level-1"><li><a href="../17784/sl-multiple-choice-tests-on-individual-topics-1.html">SL Multiple choice tests on individual topics</a></li><li><a href="../24351/sl-multiple-choice-quizzes-on-sub-topics-1.html">SL Multiple choice 'quizzes' on sub-topics</a></li><li><a href="../31519/sl-practice-paper-1-exams-1.html">SL Practice Paper 1 exams</a></li><li><a href="../17786/sl-questions-on-each-sub-topic-1.html">SL Questions on each sub-topic</a></li><li><a href="../20431/sl-paper-3-section-a-questions-1.html">SL Paper 3 Section A questions</a></li><li><a href="../17792/sl-questions-on-the-options-1.html">SL Questions on the options</a></li><li><a href="../24897/sl-quizzes-on-option-sub-topics--1.html">SL Quizzes on option sub-topics </a></li><li><a href="../17785/hl-multiple-choice-tests-on-individual-topics-1.html">HL Multiple choice tests on individual topics</a></li><li><a href="../24352/hl-multiple-choice-quizzes-on-sub-topics-1.html">HL Multiple choice 'quizzes' on sub-topics</a></li><li><a href="../31520/hl-practice-paper-1-exams--1.html">HL Practice Paper 1 exams </a></li><li><a href="../17787/hl-questions-on-each-sub-topic--1.html">HL Questions on each sub-topic </a></li><li><a href="../20428/hl-paper-3-section-a-questions-1.html">HL Paper 3 Section A questions</a></li><li><a href="../17793/hl-questions-on-the-options-1.html">HL Questions on the options</a></li><li><a href="../24973/hl-quizzes-on-option-sub-topics-1.html">HL Quizzes on option sub-topics</a></li><li><a href="../41573/printable-versions-of-written-tasks--1.html">Printable versions of written tasks </a></li></ul></li><li class="selected"><a href="../41465/complete-course-for-students--2.html">Complete course for students </a><ul class="level-1"><li><a 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<nav id="sidemenu" class="side-nav"><div class="header"><span style="color: #fff;"><a href="../41465/complete-course-for-students--2.html">Complete course for students </a></span><span id="sidetreecontrol"><a title="Collapse all" rel="collapse" href="#"><i class="fa fa-minus-circle"></i></a> <a title="Expand all" rel="expand" href="#"><i class="fa fa-plus-circle"></i></a></span></div><ul class="level-0 always-expanded"><li class=" parent" style="padding-left: 0px"><i class="expander fa fa-caret-right "></i><a href="../27988/full-coverage-of-each-topic-and-sub-topic-2.html" title="Full coverage of each topic and sub-topic">Full coverage of each topic and sub-topic</a></li><ul class="level-1 "><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../27959/topic-1-stoichiometric-relationships-1.html" title="Topic 1 : Stoichiometric relationships">Topic 1 : Stoichiometric relationships</a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27947/11-particulate-nature-of-matter-and-chemical-change--1.html" title="1.1 Particulate nature of matter and chemical change ">1.1 Particulate nature of matter and chemical change </a></li><li class=" parent" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27954/12-the-mole-concept-1.html" title="1.2 The mole concept">1.2 The mole concept</a></li><ul class="level-3 "><li class="" style="padding-left: 42px"><i class="expander fa fa-caret-right "></i><a href="../41469/comprehending-avogadros-constant-1.html" title="Comprehending Avogadro's constant">Comprehending Avogadro's constant</a></li></ul><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27958/13-reacting-masses-and-volumes--1.html" title="1.3 Reacting masses and volumes ">1.3 Reacting masses and volumes </a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../27960/topics-2-12-atomic-structure-1.html" title="Topics 2 & 12 : Atomic structure">Topics 2 & 12 : Atomic structure</a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27961/21-the-nuclear-atom--1.html" title="2.1 The nuclear atom ">2.1 The nuclear atom </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27962/22-electron-configuration--1.html" title="2.2 Electron configuration ">2.2 Electron configuration </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27963/121-electrons-in-atoms--1.html" title="12.1 Electrons in atoms ">12.1 Electrons in atoms </a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../27965/topics-3-13-periodicity-1.html" title="Topics 3 & 13 : Periodicity">Topics 3 & 13 : Periodicity</a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27966/31-the-periodic-table-1.html" title="3.1 The periodic table">3.1 The periodic table</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27967/32-periodic-trends--1.html" title="3.2 Periodic trends ">3.2 Periodic trends </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27968/131-first-row-d-block-elements-1.html" title="13.1 First-row d-block elements">13.1 First-row d-block elements</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27970/132-coloured-complexes-1.html" title="13.2 Coloured complexes">13.2 Coloured complexes</a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../27971/topics-4-14-chemical-bonding-structure-1.html" title="Topics 4 & 14 : Chemical bonding & structure">Topics 4 & 14 : Chemical bonding & structure</a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27972/41-ionic-bonding-structure--1.html" title="4.1 Ionic bonding & structure ">4.1 Ionic bonding & structure </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27973/42-covalent-bonding-1.html" title="4.2 Covalent bonding">4.2 Covalent bonding</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27974/43-covalent-structures-1--1.html" title="4.3 Covalent structures (1) ">4.3 Covalent structures (1) </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27980/43-covalent-structures-2--1.html" title="4.3 Covalent structures (2) ">4.3 Covalent structures (2) </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27981/44-intermolecular-forces--1.html" title="4.4 Intermolecular forces ">4.4 Intermolecular forces </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27982/45-metallic-bonding--1.html" title="4.5 Metallic bonding ">4.5 Metallic bonding </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27983/141-further-aspects-of-covalent-bonding-1.html" title="14.1 Further aspects of covalent bonding">14.1 Further aspects of covalent bonding</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27985/142-hybridization-1.html" title="14.2 Hybridization">14.2 Hybridization</a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../27987/topics-5-15-energeticsthermochemistry-1.html" title="Topics 5 & 15 : Energetics/thermochemistry">Topics 5 & 15 : Energetics/thermochemistry</a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27989/51-measuring-energy-changes-1.html" title="5.1 Measuring energy changes">5.1 Measuring energy changes</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27991/52-hesss-law-1.html" title="5.2 Hess's Law">5.2 Hess's Law</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27992/53-bond-enthalpies--1.html" title="5.3 Bond enthalpies ">5.3 Bond enthalpies </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27993/151-energy-cycles-1.html" title="15.1 Energy cycles">15.1 Energy cycles</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27994/152-entropy-spontaneity-1.html" title="15.2 Entropy & spontaneity">15.2 Entropy & spontaneity</a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../27995/topics-6-16-chemical-kinetics-1.html" title="Topics 6 & 16 : Chemical kinetics">Topics 6 & 16 : Chemical kinetics</a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27996/61-collision-theory-rates-of-reaction-1.html" title="6.1 Collision theory & rates of reaction">6.1 Collision theory & rates of reaction</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27997/161-rate-expression-reaction-mechanism-1.html" title="16.1 Rate expression & reaction mechanism">16.1 Rate expression & reaction mechanism</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27998/162-activation-energy-1.html" title="16.2 Activation energy">16.2 Activation energy</a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../28001/topics-7-17-equilibrium--1.html" title="Topics 7 & 17 : Equilibrium ">Topics 7 & 17 : Equilibrium </a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../27999/71-equilibrium-1.html" title="7.1 Equilibrium">7.1 Equilibrium</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28000/171-equilibrium-law-1.html" title="17.1 Equilibrium law">17.1 Equilibrium law</a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../28017/topics-8-18-acids-and-bases--1.html" title="Topics 8 & 18 : Acids and bases ">Topics 8 & 18 : Acids and bases </a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28002/81-theories-of-acids-bases-1.html" title="8.1 Theories of acids & bases">8.1 Theories of acids & bases</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28010/82-properties-of-acids-bases-1.html" title="8.2 Properties of acids & bases">8.2 Properties of acids & bases</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28011/83-ph-scale-1.html" title="8.3 pH scale">8.3 pH scale</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28012/84-strong-weak-acids-bases-1.html" title="8.4 Strong & weak acids & bases">8.4 Strong & weak acids & bases</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28013/85-acid-deposition--1.html" title="8.5 Acid deposition ">8.5 Acid deposition </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28014/181-lewis-acids-bases--1.html" title="18.1 Lewis acids & bases ">18.1 Lewis acids & bases </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28015/182-calculations-involving-acids-bases--1.html" title="18.2 Calculations involving acids & bases ">18.2 Calculations involving acids & bases </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28016/183-ph-titration-curves-1.html" title="18.3 pH titration curves">18.3 pH titration curves</a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../28031/topics-9-19-redox-process-1.html" title="Topics 9 & 19 : Redox process">Topics 9 & 19 : Redox process</a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28021/91-oxidation-reduction-1.html" title="9.1 Oxidation & reduction">9.1 Oxidation & reduction</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28022/92-electrochemical-cells-1.html" title="9.2 Electrochemical cells">9.2 Electrochemical cells</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28023/191-electrochemical-cells-ahl-1.html" title="19.1 Electrochemical cells (AHL)">19.1 Electrochemical cells (AHL)</a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../28061/topics-10-20-organic-chemistry-1.html" title="Topics 10 & 20 : Organic chemistry">Topics 10 & 20 : Organic chemistry</a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28042/101-fundamentals-of-organic-chemistry-1.html" title="10.1 Fundamentals of organic chemistry">10.1 Fundamentals of organic chemistry</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28043/1021-alkanes-alkenes-addition-polymers-1.html" title="10.2(1) Alkanes, alkenes & addition polymers">10.2(1) Alkanes, alkenes & addition polymers</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28044/1022-alcohols--1.html" title="10.2(2) Alcohols ">10.2(2) Alcohols </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28047/1023-halogenoalkanes-benzene-1.html" title="10.2(3) Halogenoalkanes & benzene">10.2(3) Halogenoalkanes & benzene</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28050/2011-nucleophilic-substitution--1.html" title="20.1(1) Nucleophilic substitution ">20.1(1) Nucleophilic substitution </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28051/2012-electrophilic-addition--1.html" title="20.1(2) Electrophilic addition ">20.1(2) Electrophilic addition </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28053/2013-electrophilic-substitution-1.html" title="20.1(3) Electrophilic substitution">20.1(3) Electrophilic substitution</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28054/2014-reduction-reactions--1.html" title="20.1(4) Reduction reactions ">20.1(4) Reduction reactions </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28056/202-synthetic-routes--1.html" title="20.2 Synthetic routes ">20.2 Synthetic routes </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28059/203-stereoisomerism--1.html" title="20.3 Stereoisomerism ">20.3 Stereoisomerism </a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../28038/topics-11-21-measurement-data-processing-analysis-1.html" title="Topics 11 & 21 : Measurement, data processing & analysis">Topics 11 & 21 : Measurement, data processing & analysis</a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28032/111-uncertainty-errors--1.html" title="11.1 Uncertainty & errors ">11.1 Uncertainty & errors </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28033/112-graphical-techniques-1.html" title="11.2 Graphical techniques">11.2 Graphical techniques</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28034/113-spectroscopic-identification-of-organic-compounds-1.html" title="11.3 Spectroscopic identification of organic compounds">11.3 Spectroscopic identification of organic compounds</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28039/211-spectroscopic-identification-of-organic-compounds-ahl-1.html" title="21.1 Spectroscopic identification of organic compounds (AHL)">21.1 Spectroscopic identification of organic compounds (AHL)</a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../28074/option-a-materials--1.html" title="Option A : Materials ">Option A : Materials </a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28062/a1-introduction-to-materials-science--1.html" title="A.1 Introduction to materials science ">A.1 Introduction to materials science </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28063/a2-metals-and-icp-spectroscopy-1.html" title="A.2 Metals and ICP spectroscopy">A.2 Metals and ICP spectroscopy</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28065/a3-catalysts--1.html" title="A.3 Catalysts ">A.3 Catalysts </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28066/a4-liquid-crystals-1.html" title="A.4 Liquid crystals">A.4 Liquid crystals</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28067/a5-polymers-1.html" title="A.5 Polymers">A.5 Polymers</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28069/a6-nanotechnology-1.html" title="A.6 Nanotechnology">A.6 Nanotechnology</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28070/a7-environmental-impact-plastics-1.html" title="A.7 Environmental impact - plastics">A.7 Environmental impact - plastics</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28071/a8-superconducting-metals-x-ray-crystallography--1.html" title="A.8 Superconducting metals & X-ray crystallography ">A.8 Superconducting metals & X-ray crystallography </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28072/a9-condensation-polymers-1.html" title="A.9 Condensation polymers">A.9 Condensation polymers</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28073/a10-environmental-impact-heavy-metals-1.html" title="A.10 Environmental impact - heavy metals">A.10 Environmental impact - heavy metals</a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../28087/option-b-biochemistry-1.html" title="Option B : Biochemistry">Option B : Biochemistry</a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28076/b1-introduction-to-biochemistry--1.html" title="B.1 Introduction to biochemistry ">B.1 Introduction to biochemistry </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28078/b2-proteins-enzymes-1.html" title="B.2 Proteins & enzymes">B.2 Proteins & enzymes</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28079/b3-lipids-1.html" title="B.3 Lipids">B.3 Lipids</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28080/b4-carbohydrates-1.html" title="B.4 Carbohydrates">B.4 Carbohydrates</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28081/b5-vitamins-1.html" title="B.5 Vitamins">B.5 Vitamins</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28082/b6-biochemistry-the-environment-1.html" title="B.6 Biochemistry & the environment">B.6 Biochemistry & the environment</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28083/b7-proteins-enzymes-ahl--1.html" title="B.7 Proteins & enzymes (AHL) ">B.7 Proteins & enzymes (AHL) </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28084/b8-nucleic-acids-1.html" title="B.8 Nucleic acids">B.8 Nucleic acids</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28085/b9-biological-pigments-1.html" title="B.9 Biological pigments">B.9 Biological pigments</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28086/b10-stereochemistry-in-biomolecules-1.html" title="B.10 Stereochemistry in biomolecules">B.10 Stereochemistry in biomolecules</a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../28098/option-c-energy--1.html" title="Option C : Energy ">Option C : Energy </a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28088/c1-energy-sources--1.html" title="C.1 Energy sources ">C.1 Energy sources </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28089/c2-fossil-fuels-1.html" title="C.2 Fossil fuels">C.2 Fossil fuels</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28090/c3-nuclear-fusion-nuclear-fission-reactions-1.html" title="C.3 Nuclear fusion & nuclear fission reactions">C.3 Nuclear fusion & nuclear fission reactions</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28091/c4-solar-energy--1.html" title="C.4 Solar energy ">C.4 Solar energy </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28094/c5-environmental-impact-global-warming--1.html" title="C.5 Environmental impact - global warming ">C.5 Environmental impact - global warming </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28095/c6-electrochemistry-rechargeable-batteries-fuel-cells-1.html" title="C.6 Electrochemistry, rechargeable batteries & fuel cells">C.6 Electrochemistry, rechargeable batteries & fuel cells</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28096/c7-nuclear-fusion-fission-hl--1.html" title="C.7 Nuclear fusion & fission (HL) ">C.7 Nuclear fusion & fission (HL) </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28097/c8-photovoltaic-cells-and-dsscs-1.html" title="C.8 Photovoltaic cells and DSSCs">C.8 Photovoltaic cells and DSSCs</a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../28109/option-d-medicinal-chemistry-1.html" title="Option D : Medicinal chemistry">Option D : Medicinal chemistry</a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28099/d1-pharmaceutical-products-drug-action--1.html" title="D.1 Pharmaceutical products & drug action ">D.1 Pharmaceutical products & drug action </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28100/d2-aspirin-penicillin-1.html" title="D.2 Aspirin & penicillin">D.2 Aspirin & penicillin</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28101/d3-opiates-1.html" title="D.3 Opiates">D.3 Opiates</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28103/d4-ph-regulation-of-the-stomach-1.html" title="D.4 pH regulation of the stomach">D.4 pH regulation of the stomach</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28102/d5-antiviral-medications-1.html" title="D.5 Antiviral medications">D.5 Antiviral medications</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28104/d6-environmental-impact-of-some-medications-1.html" title="D.6 Environmental impact of some medications">D.6 Environmental impact of some medications</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28105/d7-taxol-a-chiral-auxiliary-case-study--1.html" title="D.7 Taxol - a chiral auxiliary case study ">D.7 Taxol - a chiral auxiliary case study </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28107/d8-nuclear-medicine--1.html" title="D.8 Nuclear medicine ">D.8 Nuclear medicine </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../28108/d9-drug-detection-analysis-1.html" title="D.9 Drug detection & analysis">D.9 Drug detection & analysis</a></li></ul></ul><li class=" parent" style="padding-left: 0px"><i class="expander fa fa-caret-right "></i><a 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</div><section id="main-content"><div class="blueBg"><h1>What do 'curly arrows' represent?</h1><hr class="hidden"><p><img alt="" class="noborder" longdesc="" src="../../../ib/chemistry/images/2014%20Exams/curly-arrow1008-.jpg" style="width: 350px; height: 371px; float: right;" title="Artwork by Birgit Jennings, formerly Head of Art at Geneva International School">The correct use of curly arrows can cause real problems – both to students (and teachers) and examiners. The main reason why students fail to score marks is that they use the arrows completely wrongly but even when arguably they have been used correctly students can still fail to score marks depending on how examiners interpret the markscheme. What I hope to show is how you can use them correctly so that you can be certain to get full marks. I have included a slide presentation you which also emphasises the main points.</p><h3>Definition</h3><p>One of the main problems is the definition of what a ‘curly arrow’ actually means. The best definition and the one used by the IB can be found on the website hosted by <a href="http://www.abdn.ac.uk/curly-arrows/org/curl.shtml">Aberdeen University</a> and this is supported by the Royal Society of Chemistry.</p><p style="margin-left: 40px;">“Curly arrows are the notation used by organic chemists to indicate the movement of electrons when bonds are made, broken, or moved.</p><p style="margin-left: 40px; ">A ‘curly arrow’ represents the movement of an electron <strong>pair</strong> from its original position to a new one. The tail of the arrow shows where the electron pair has come from, and the head of the arrow shows where the electron pair is going to.”</p><hr class="hidden"></div> <hr class="hidden"><div class="greenBg"><h1>Common errors made by students</h1><p><strong>1. Showing the arrow the wrong way round.</strong> Typically when showing the electrophilic addition reaction of H—Br with an alkene the arrow comes from the H—Br to the alkene – not the other way round.</p><hr class="hidden"><p style="text-align: center; "><img alt="" class="noborder" height="239" src="../../../ib/chemistry/images/Exams/Curly arrows (a).JPG" width="448"></p><hr class="hidden"><p><strong>2. Starting the arrow in the wrong place.</strong> This is often seen when the hydroxide ion is used as the nucleophile in a nucleophilic substitution reaction with a halogenoalkanes. The arrow must start either from the negative charge on the hydroxide ion or even better from a non-bonding pair of electrons on the hydroxide ion. It will be penalised if it is shown originating from the hydrogen atom.</p><hr class="hidden"><p style="text-align: center; "><img alt="" class="noborder" height="336" src="../../../ib/chemistry/images/Exams/Curly arrows (b).JPG" width="415"></p><hr class="hidden"><p><strong>3. Finishing the arrow in the wrong place.</strong> There is some disagreement with some examiners here who have been brought up to draw the arrow going directly to the carbon atom in a nucleophilic substitution reaction. From the definition the arrow should end up where the bond will be formed which will be between the carbon atom and the HO– group when it is bonded.</p><hr class="hidden"><p style="text-align: center; "><img alt="" class="noborder" height="336" src="../../../ib/chemistry/images/Exams/Curly arrows (c).JPG" width="341"></p><hr class="hidden"><p>The above three errors are all due to students misunderstanding what a ‘curly arrow’ represents. There is a further problem which is best represented by an actual IB question and two different answers given by two students. The question was:</p><hr class="hidden"><p style="text-align: center; "><img alt="" class="noborder" height="274" src="../../../ib/chemistry/images/Exams/Curly arrow (1).jpg" width="550"></p><hr class="hidden"><p>This initial information in the introduction to the question could be criticised as in part (II) it show the ‘curly arrow’ going right to the carbon atom instead of where the electron pair should end up which is in the middle of the line between C and O in the product. However, as some teachers and text books do use this approach, it would not be penalised if a student had done this in a written answer.</p><p>The question then went on:</p><hr class="hidden"><p style="text-align: center; "><img alt="" class="noborder" height="85" src="../../../ib/chemistry/images/Exams/Curly arrow (2).jpg" width="550"></p><hr class="hidden"><p>The markscheme actually had four marking points so if a student scored any three of them they would get the full three marks.</p><p>These marking points were:</p><p>1. Showing a curly arrow from the O or the non-bonding pair on the O or the negative charge on the O on the OH<sup>– </sup>ion<sup> </sup>towards the C of C—Br.</p><p>2. A correct representation of the transition state showing partial bonds and a negative charge.</p><p>3. Curly arrow from the C—Br bond to the bromine to form Br<sup>-</sup>.</p><p>4. Correct products.</p><hr class="hidden"><p>Now let’s look at a genuine student answer.</p><hr class="hidden"><p style="text-align: center; "><img alt="" class="noborder" height="221" src="../../../ib/chemistry/images/Exams/Curly arrow (3).jpg" width="550"></p><hr class="hidden"><p>I personally think that this student got three of the four points correct (they missed the curly arrow from the C—Br bond) so I would have awarded full marks if I had been in charge of the paper. It seems clear to me that the student understands the chemistry.</p><p>However several examiners argued that the first curly arrow is going to the wrong place as it would be repelled by the existing pair of electrons in the C—Br bond and the two partial bonds are too close in the transition state as they should be 180<sup>o</sup> apart. I can see their logic but I disagree. For the first point the arrow is shown going to exactly where it will end up in the product and in the transition state it depends on how the three-dimensional shape is represented in two-dimensions. This latter point is, I think, the root cause of many ‘curly arrow’ problems. I think it is best to always show the mechanism in the normally accepted three-dimensional representation and in fact this is specifically mentioned in sub-topic 20.1: Types of organic reactions in the AHL programme. That way there can be no doubt about the fact that the nucleophile is attacking the carbon from the opposite side of its bond to the halogen and that the five-membered transition state has a trigonal bipyramidal shape. I enclose the diagram on page 226 of the 2nd Edition of my Chemistry Course Companion to show this.</p><hr class="hidden"><p style="text-align: center; "><img alt="" class="noborder" height="125" src="../../../ib/chemistry/images/Exams/Curly arrow (5).jpg" title="Diagram showing correct use of curly arrows for a S<sub>N</sub>2 reaction taken from the 2nd edition of my Chemistry Course Companion" width="537"></p><hr class="hidden"></div><hr class="hidden"><div class="pinkBg"><h2>Further points</h2><p>You might wish to go on and add some TOK to your understanding as Paul Walden, (1863-1957) a Latvian chemist reasoned that if an S<sub>N</sub>2 mechanism took place with a secondary halogenoalkane then the product would rotate the plane of light in the opposite direction to the halogenoalkane reactant. This was indeed found to be the case and provides good evidence to support our picture of chemistry at the molecular level.</p><p>It is also worth knowing that organic chemists use a 'curly arrows' with a 'half-head' (fish hook) to represent the movement of a single electron as this is detailed in the "Guidance" section of sub-topic 20.1. Fish hooks are used when explaining free radical mechanisms, for example the homolytic fission of a chlorine molecule by ultraviolet light to form two chlorine radicals.</p><p>If you want some more examples then Oxford University have produced a useful <a href="http://www.chem.ox.ac.uk/vrchemistry/iom/default.html">Website</a> which contains a tutorial and also has a fun section where you can test your skills at drawing the arrows in the correct places.</p></div><hr class="hidden"><div class="greenBg"><p>The following slide presentation can be used to illustrate the above points.</p><div id="myCarousel-1" class="carousel slide" data-id="317"><!-- Carousel items --><div class="carousel-inner"><div class="active item"><a class="fancy" href="../../../tib-galleries/3-317/ca1.png" rel="gallery-317" title=""><img alt="" src="files/tib-galleries/3-317/ca1.png"></a><div class="carousel-caption"><p>Problems using 'curly arrows': </p></div></div><div class="item"><a class="fancy" href="../../../tib-galleries/3-317/ca2.png" rel="gallery-317" title=""><img alt="" src="files/tib-galleries/3-317/ca2.png"></a><div class="carousel-caption"><p>Problems using 'curly arrows': </p></div></div><div class="item"><a class="fancy" href="../../../tib-galleries/3-317/ca3.png" rel="gallery-317" title=""><img alt="" src="files/tib-galleries/3-317/ca3.png"></a><div class="carousel-caption"><p>Problems using 'curly arrows': </p></div></div><div class="item"><a class="fancy" href="../../../tib-galleries/3-317/ca4.png" rel="gallery-317" title=""><img alt="" src="files/tib-galleries/3-317/ca4.png"></a><div class="carousel-caption"><p>Problems using 'curly arrows': </p></div></div><div class="item"><a class="fancy" href="../../../tib-galleries/3-317/ca5.png" rel="gallery-317" title=""><img alt="" src="files/tib-galleries/3-317/ca5.png"></a><div class="carousel-caption"><p>Problems using 'curly arrows': </p></div></div><div class="item"><a class="fancy" href="../../../tib-galleries/3-317/ca6.png" rel="gallery-317" title=""><img alt="" src="files/tib-galleries/3-317/ca6.png"></a><div class="carousel-caption"><p>Problems using 'curly arrows': </p></div></div></div><!-- Carousel nav --><a class="carousel-control left" href="#myCarousel-1" data-slide="prev">‹</a><a class="carousel-control right" href="#myCarousel-1" data-slide="next">›</a><div class="tib-indicators"><img class="" title="Click to view" style="margin: 10px 4px; 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