3 Boardworks IGCSE Chemistry Ionic Compounds Different compoundsBoardworks IGCSE ChemistryIonic CompoundsThere are four different types of compounds. These are:ionic compoundssimple molecular covalent compoundsgiant molecular covalent compoundsmetallic compounds.The type of bonding in a compound affects its physical properties, including melting and boiling points, solubility and electrical conductivity.Compounds that contain ions are called ionic compounds.The positive and negative ions are strongly attracted to each other. This electrostatic attraction is called ionic bonding.
4 Boardworks IGCSE Chemistry Ionic Compounds What is ionic bonding?Boardworks IGCSE ChemistryIonic CompoundsTeacher notesThis two-part interactive animation shows how bonding occurs in two compounds – sodium chloride and magnesium oxide. It shows how the ions are formed, which electrons are transferred and how this leads to the formation of the ionic lattices.
5 What is an ionic lattice? Boardworks IGCSE ChemistryIonic CompoundsIn an ionic compound, millions and millions of ions are packed together in a regular lattice arrangement, joined by strong ionic bonds between oppositely-charged ions.This forms a giant 3D structure called an ionic lattice.The ionic lattice will continue to build in this way until there are no more ions left to add.The structure of the ionic lattice affects the properties of the ionic compound.
6 Why do ionic compounds form crystals? Boardworks IGCSE ChemistryIonic CompoundsIonic compounds such as sodium chloride, form crystals, with a cubic shape. This is due to the regular structure of the ionic lattice.Teacher notesThe image is a coloured scanning electron micrograph (SEM) of common salt, sodium chloride, recrystallized from distilled water. The salt crystal is built up from a cubic lattice of sodium and chloride ions. In the absence of impurities the exact cubic crystal form is produced. This micrograph shows that in practice this basic cube is usually disrupted by dislocations; these give rise to crystals with a variety of shapes, although they all retain the basic cubic symmetry. Magnification: x280 at 5x7cm size. x975 at 10x8‘.Photo credit: Andrew Syred/Science Photo Library.All ionic compounds form lattices and crystals when solid.
7 Heating ionic compounds Boardworks IGCSE ChemistryIonic CompoundsWhy are ionic compounds solid at room temperature and have high melting points and boiling points?ion chargesmelting point (oC)boiling point (oC)compoundsodium chloride1+ and 1-8011,413magnesium oxide2+ and 2-2,8523,600strong ionic bonds hold ions togetherIonic bonds are strong and a lot of heat is needed to break them.Larger ionic charges produce stronger ionic bonds and so much more heat is required to break the ionic bonds in magnesium oxide than in sodium chloride.
8 How do ionic compounds dissolve? Boardworks IGCSE ChemistryIonic Compounds
9 Electrical conductivity Boardworks IGCSE ChemistryIonic CompoundsTeacher notesThis virtual experiment illustrates which substances, and in what state, conduct electricity and why. It could be used as a precursor to running the practical in the lab, or as a revision exercise.You may wish to remind students that all ionic compounds, including magnesium oxide (MgO), conduct electricity when molten or in solution.See the presentation Covalent Bonding for more information about covalent bonding.
10 How can ionic compounds conduct electricity? Boardworks IGCSE ChemistryIonic CompoundsAs solids, ionic compounds cannot conduct electricity because their ions arebonded together in the lattice.ions in solid state cannot moveWhen liquid (molten), the ions can break free of the lattice and are able to move. The ions are charged particles and so can carry an electric current.ions inmolten state can moveand conduct electricityIonic compounds are usually soluble in water because water molecules have a slight electrical charge and so can attract the ions away from the lattice. When dissolved, the ions are free to move and can carry an electric current.
11 Boardworks IGCSE Chemistry Ionic Compounds The worksheet Ionic Bonding.doc accompanies this presentation.
12 Boardworks IGCSE Chemistry Ionic Compounds GlossaryBoardworks IGCSE ChemistryIonic CompoundsTeacher notesbond – A strong force that joins atoms or ions together in molecules and giant lattices.ion – An atom or group of atoms that has an electrical charge, either positive or negative.ionic bond – The electrostatic force of attraction between oppositely-charged ions.ionic compound – A compound made up of ions.ionic lattice – A giant 3D structure of closely packed, oppositely-charged ions.negative ion – An atom or group of atoms that has gained electrons and so has a negative charge.positive ion – An atom or group of atoms that has lost electrons and so has a positive charge.
13 Ionic compounds – true or false? Boardworks IGCSE ChemistryIonic CompoundsTeacher notesThis true-or-false activity could be used as a plenary or revision exercise on the properties of ionic compounds, or at the start of the lesson to gauge students’ existing knowledge of the subject matter. Coloured traffic light cards (red = false, yellow = don’t know, green = true) could be used to make this a whole-class exercise.
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