[note][tr] Diversity 1.1 Ionic Bonding 2024 [modofied for 2025 9 july 2024]

1 D 1.2 Ionic Bonding CHIJ ST. NICHOLAS GIRLS’ SCHOOL Sec 2 Science 2024[modified for 2025 9 july 2024] Diversity 1 : Exploring Diversity of Matter by their Physical properties D 1.1 Ionic Bonding Students should be able to : (a) Describe the formation of ionic bonds between metals and non-metals eg in NaCl and MgCl2, using ‘dot and cross’ diagrams to illustrate (b) State that ionic materials contain a giant lattice in which the ions are held by electrostatic attraction, e.g. NaCl (diagrams of ionic lattices will not be required) (c) Deduce the formulae of other ionic compounds from diagrams of their lattice structures, limited to binary compounds (d) Relate the physical properties (including electrical property of ionic compounds to their lattice structure) (e) Explain how to derive the chemical formula from the charges of the ions present Students should be able to : (a) explain the choice of the main classes of materials (metals, ceramics, glass, plastics, fibres) in the production of common household items, in terms of their properties, e.g. density ,strength, hardness, flexibility, electrical conductivity, thermal conductivity, boiling/melting point (b) use data on the properties of different materials to evaluate their uses (c) relate the properties of substances to type of bonding and structure :

2 D 1.2 Ionic Bonding Ionic Bond What are ions? : http://youtu.be/900dXBWgx3Y 1. Ions are formed when atoms loses outer/valence shell electrons or gain electrons into the outer/valence shell. 2. The charge on the ion is either positive or negative. 3. If an atom loses electrons, the ion formed is positively charged because the number of protons present is more than the number of electrons left. 4. If an atom gains electrons, the ion formed is negatively charged because the number of electron is more than the number of protons. Ionic compound An ionic compound is formed when a metal reacts with a non-metal. The metal atom loses electrons to the non-metal aroms. This results in forming positive metal ions and negative non-metal ions. These oppositely charged ions are attracted together to form ionic compound. http://youtu.be/zpaHPXVR8WU Using the reaction between sodium and chlorine as an example:  Cations and anions are attracted to one another through strong electrostatic forces of attraction. This constitutes an ionic bond.  The compound formed is called sodium chloride. Definition of ionic bond An ionic bond is the strong electrostatic forces of attraction between oppositely charged ions.  Metallic atoms lose their valence electrons to non-metallic atoms.  Metallic atoms become positive ions (cations).  Non-metallic atoms become negative ions (anions).

3 D 1.2 Ionic Bonding More practice Draw the ‘dot and cross’ diagrams to show the electronic structures of ionic compounds formed by the following elements. Show all the electrons. (answers on the power point) a) Lithium and fluorine Chemical name: …………………… Chemical formula: …………………….. b) Beryllium and oxygen Chemical name: …………………… Chemical formula: …………………….. c) Potassium and oxygen Chemical name: …………………… Chemical formula: …………………….. d) Aluminium and sulfur Chemical name: …………………… Chemical formula: …………………….. e) Sodium and oxygen Chemical name: …………………… Chemical formula: …………………….. f) Aluminium and nitrogen Chemical name: …………………… Chemical formula: ……………………..

4 D 1.2 Ionic Bonding For the following two compounds, draw only the valence electrons, given that bromine (Br) is in Group VII of the Periodic Table, while rubidium (Rb) is in Group I. g) Calcium and bromine Chemical name: …………………… Chemical formula: …………………….. h) Rubidium and chlorine Chemical name: …………………… Chemical formula: ……………………..

5 D 1.2 Ionic Bonding Physical properties of Ionic Compounds https://www.youtube.com/watch?v=NfNIn4R8tg4 In the solid state, an ionic compound has a regular arrangement of alternating positive and negative ions. This regular arrangement is known as a giant ionic lattice. Using sodium chloride as an example, • The ions are arranged in a giant ionic structure in a regular repeating manner. • Each sodium ion is surrounded by 6 chloride ions, and each chloride ion is in turn surrounded by 6 sodium ions. • Thus the ratio of sodium ions to chloride ions is 1:1. • Ionic compounds which have ions of equal and opposite charge will have the same structure as sodium chloride, NaCl, MgO, CaO, KFand etc but not MgCl2, Na2O and etc Cl–: chloride ion Na+: sodium

6 D 1.2 Ionic Bonding Physical properties of compounds with Giant Ionic Structure Property Explanation Melting point and boiling point  High and usually exist as solids at room temperature and pressure e.g. NaCl (m.p 801 oC, b.p. 1465 oC)  They have ionic bonding and giant ionic structure.  A large amount of energy is needed to overcome the strong electrostatic forces of attraction between the oppositely-charged ions in the giant ionic lattice structure. Electrical Conductivity https://www.youtube.com/watch?v=NfNIn4R8tg4  Unable to conduct electricity in the solid state but can do so in the molten and aqueous states.  They have a giant ionic structure.  In the solid state, the oppositely charged ions can only vibrate about their fixed positions due to the strong electrostatic forces of attraction. Therefore, the ions are not mobile to conduct electricity.  In the aqueous/molten state, this attractive weakened. Hence, the ions become mobile and are able to conduct electricity. Solubility  Mostly soluble in water (FYI) water molecules can separate the positive ions from the negative ions and surround them, forming new interactions with the ions.

7 D 1.2 Ionic Bonding Factor affecting the strength of ionic bonds Substances Melting point/°C Sodium chloride 801 Magnesium oxide 2852 Based on the information given above, what affects the strength of ionic bonds? The higher charge of the ions, the stronger its ionic bonds (electrostatic forces of attraction) Explain why MgO has higher melting point than NaCl. Mg 2+ has higher ionic charge than Na + . O 2- has higher ionic charge than Cl - . More energy is needed to overcome the stronger electrostatic forces of attraction between oppositely charged ions (Mg 2+ and O 2- ).

8 D 1.2 Ionic Bonding Chemical formula of ionic compounds The formula of an ionic compound is derived by balancing the charges on the positive ions with those on the negative ions. All the positive charges must equal all the negative charges in an ionic compound. For instance, aluminum sulfate consists of aluminum cations and sulfate anions (A) For simple ions View the following video : Writing Ionic Formulas: Introduction (https://www.youtube.com/watch?v=URc75hoKGLY) Practice Write down the chemical formulas of each of the following compounds : Name of compound Formula of positive ion Formula of negative ion Chemical formula of compound 1 sodium fluoride Na + F - NaF 2 calcium chloride Ca2+ Cl- CaCl2 3 aluminium fluoride Al3+ F- AlF3 4 potassium oxide K+ O2- K2O 5 magnesium sulfide Mg2+ S2- MgS 6 iron(III) oxide Fe 3+ O2- Fe2O3 Al2(SO4)3 Subscript 3 refers to everything inside the parentheses giving 3 sulfate ions, with a total of 3 sulfur atoms and 12 oxygen atoms Subscript 4 refers to 4 oxygen atoms in the sulfate ion Note: when you only have one ion, no subscript is used Subscript 2 refers to 2 aluminum ions

9 D 1.2 Ionic Bonding (B) For polyatomic ions A polyatomic ion, is a