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<meta name="description" content="For some reason many students seem to find it very difficult to predict the shape and bond angles of a simple molecule or ion using Valence Shell Electron Pair Repulsion Theory (VSEPR). At first sight this seems strange because the theory really is very simple. Essentially there are only three basic ideas:Applying the first idea leads to the fact that there are only five basic shapes to be considered. In fact there are...">
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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 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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 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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>The theory</h1><p>For some reason many students seem to find it very difficult to predict the shape and bond angles of a simple molecule or ion using Valence Shell Electron Pair Repulsion Theory (<span data-scayt-word="VSEPR" data-wsc-lang="en_US">VSEPR</span>). At first sight this seems strange because the theory really is very simple. Essentially there are only three basic ideas:</p><hr class="hidden"><ul class="branded"><li>Electrons arrange themselves in pairs around the central atom or ion so that there is maximum repulsion between the pairs. Strictly speaking it is electron domains rather than electron pairs as this would take account of an unpaired electron in a free radical but this is not necessary at this level. In fact in previous syllabi the term 'negative charge <span data-scayt-word="centres" data-wsc-lang="en_US">centres</span>' was used but in sub-topic 4.3 : Covalent structures it clearly states that 'electron domain' should be used in place of 'negative charge centre'.<br> </li><li>Non-bonding pairs of electrons exert a greater repulsion than bonded pairs.<br> </li><li>A multiple bond (i.e. a double or triple bond) must count as one pair of electrons (one electron domain) as all the pairs of electrons must be aligned in the same direction.</li></ul><hr class="hidden"><p>Applying the first idea leads to the fact that there are only five basic shapes to be considered. In fact there are only three at Standard Level as sub-topic 4.3 limits the shape to two, three and four electron domains on the central atom. For Higher Level students sub-topic 14.1 extends this to five and six pairs. These basic shapes and bond angles are:</p><hr class="hidden"><table align="center" border="1" cellpadding="20" cellspacing="2"><tbody><tr><td style="background-color: rgb(153, 204, 204);"><strong>Number of pairs of electrons</strong></td><td style="background-color: rgb(153, 204, 204);"><strong>Shape</strong></td><td style="background-color: rgb(153, 204, 204);"><strong>Bond angle(s)</strong></td></tr><tr><td style="text-align: center">2</td><td>Linear</td><td>180<sup>o</sup></td></tr><tr><td style="text-align: center">3</td><td>Trigonal planar</td><td>120<sup>o</sup></td></tr><tr><td style="text-align: center">4</td><td>Tetrahedral</td><td>109.5<sup>o</sup> (actually 109<sup>o</sup> 28')</td></tr><tr><td style="text-align: center">5</td><td>Trigonal bipyramidal</td><td>90<sup>o</sup>, 120<sup>o</sup>, 180<sup>o</sup></td></tr><tr><td style="text-align: center">6</td><td>Octahedral</td><td>90<sup>o</sup>, 180<sup>o</sup></td></tr></tbody></table><hr class="hidden"><p>If one or more pairs are non-bonded then the basic shape adapts to take account of this. An example is ammonia.</p><hr class="hidden"><p><img alt="" class="left noborder" src="../../../ib/chemistry/images/Exams/ammonia shape.png" style="width: 217px; height: 189px; float: left;" title="Trigonal pyramidal shape of a molecule of ammonia">There are four pairs of electrons around the central nitrogen atom. Three of these are bonding and one is non-bonding. Four pairs gives a tetrahedral shape but as one of the pairs is a non-bonding pair the actual shape will be trigonal pyramid (with the non-bonded pair pointing to the apex of what would have been the tetrahedron). As the non-bonding pair exerts a greater repulsion than bonding pairs this forces the bonded pairs slightly closer together and the H-N-H bond angle is reduced from the 109.5<sup>o </sup> of a regular tetrahedron to approximately 107<sup>o</sup>. Other examples follow a similar logic and basically that is all there is to it - at least as far as the IB goes. In fact it is not nearly so simple when you try to extend it to other molecules and ions. You can read more about this in 'Something to think about' on the page covering shapes of molecules or ions in <a href="../27980/43-covalent-structures-2--1.html" title="Complete course for students » Topics 4 & 14 : Chemical bonding & structure » 4.3 Covalent structures (2) ">4.3 Covalent structures (2)</a>. </p><hr class="hidden"></div><hr class="hidden"><div class="greenBg"><h1>The problem for students</h1><p>So why do many students seem to find it so difficult? I think there are two fundamental reasons. The first is that they are not clear about how to determine the number of electron pairs around the <strong>central</strong> atom. To do this they need to understand about Lewis structures but then ignore all the electron pairs around all the outer atoms. At Standard Level they can use the octet rule to give them the number and almost all examples will be four pairs due to the eight electrons around the central atom. However, because some of the pairs might be a double or triple bond this will reduce the number of pairs according to <span data-scayt-word="VSEPR" data-wsc-lang="en_US">VSEPR</span> theory. So that, for example, a carbon dioxide molecule which has the eight electrons around the central carbon atom arranged in two double bonds will have two pairs according to <span data-scayt-word="VSEPR" data-wsc-lang="en_US">VSEPR</span> and is linear. </p><p>The second reason is that many students seem unable to visualize the shapes in three dimensions. There is an interesting article about this written by Ashley Jennings, a high school student from Pennsylvania, in <a href="/media/ib/chemistry/files/VSEPR%20article.pdf">Journal of Chemical Education, Vol. 87 No. 5 May 2010 pages 462-463</a>. In this article Ashley talks about how difficult it was for students to equate two-dimensional drawings with the three-dimensional models the teacher had <strong>shown</strong> them. Ashley's solution to this was to develop her own video showing the models in three dimensions.</p><hr class="hidden"><p style="text-align: center"><iframe allowfullscreen="" frameborder="0" height="280" src="//www.youtube.com/embed/i3FCHVlSZc4?rel=0" width="360"></iframe></p><p style="text-align: center;"><a href="http://youtu.be/i3FCHVlSZc4">VSEPR theory <img class="ico" src="../../../img/icons/video-1.png"><span class="anchor" id="video-1" name="video-1"> </span></a></p><hr class="hidden"><p>This is a well-constructed video and you may find it helpful. I think though that the real problem is that often students are only <strong>shown</strong> the shapes and even in this video the shapes are <strong>shown</strong> on a two-dimensional screen. I have found that you will gain a much better understanding and concept of the shapes if you <strong>make your own models</strong>. Ideally you should have access to a molecular modelling kit, <a href="http://www.molymod.com/">e.g. molymod </a>and you should ask your teacher to buy the kits if your school does not already have them. If you always have these kits at hand then whenever a shape is discussed you can make the shape for yourself and feel it in three-dimensions.</p><p>Finally, if you are still having problems, it might be worth just learning the shapes of some specific molecules and ions as the examples the IB can use are quite limited in number!</p><hr class="hidden"></div></section></article><section id="media-extras"><div class="page-actions no-print navbar inline hidden-desktop"><div class="navbar-inner"><ul class="nav"><li><a class="presentation" href="#" onclick="return false;"><i class="fa fa-desktop"></i></a></li><li><a class="print-section-blog" href="#" onclick="return false;"><i class="fa fa-print"></i></a></li><li><a class="page-bookmarker" data-ticket="IB Docs (2) Team" data-pid="41422" href="#" onclick="return false;"><i class="fa fa-star"></i></a></li><li><a class="personal-notes" href="#" onclick="return false;"><i class="fa fa-file-text"></i></a></li><li><a class="" data-toggle="modal" href="#modal-feedback" onclick="return false;"><i class="fa fa-envelope-o"></i></a></li><li class="dropdown"><a class="dropdown-toggle" data-toggle="dropdown" data-target="#" href="#"><i class="fa fa-share-alt"></i></a><ul class="dropdown-menu" role="menu"><li><a class="" target="_blank" title="Share on Twitter" href="https://twitter.com/share?text=%22VSEPR%22+-+via+%40InThinker+%23chemistry%0A&url=https%3A%2F%2Fwww.thinkib.net%2Fchemistry%2Fpage%2F41422%2Fvsepr"><i class="fa fa-twitter-square"></i><span>Twitter</span></a></li><li><a class="" target="_blank" title="Share on Facebook" href="https://www.facebook.com/sharer.php?u=https%3A%2F%2Fwww.thinkib.net%2Fchemistry%2Fpage%2F41422%2Fvsepr&t=VSEPR"><i class="fa fa-facebook-square"></i><span>Facebook</span></a></li><li><a class="" href="http://www.linkedin.com/shareArticle?mini=true&url=https%3A%2F%2Fwww.thinkib.net%2Fchemistry%2Fpage%2F41422%2Fvsepr"><i class="fa fa-linkedin-square"></i><span>LinkedIn</span></a></li><li><a class="" href="https://plus.google.com/share?url=https%3A%2F%2Fwww.thinkib.net%2Fchemistry%2Fpage%2F41422%2Fvsepr"><i class="fa fa-google-plus-square"></i><span>Google +</span></a></li><li><a class="" href="mailto:?subject=VSEPR&body=For some reason many students seem to find it very difficult to predict the shape and bond angles of a simple molecule or ion using Valence Shell Electron Pair Repulsion Theory (VSEPR). 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